Vision, Reading Difficulties, and Visual Stress 3031039297, 9783031039294

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Vision, Reading Difficulties, and Visual Stress Arnold J. Wilkins Bruce J. W. Evans Second Edition

Vision, Reading Difficulties, and Visual Stress

Arnold J. Wilkins Bruce J. W. Evans •

Vision, Reading Difficulties, and Visual Stress Second Edition

123

Arnold J. Wilkins (Emeritus) Department of Psychology University of Essex Colchester, UK

Bruce J. W. Evans Institute of Optometry London, UK

ISBN 978-3-031-03929-4 ISBN 978-3-031-03930-0 https://doi.org/10.1007/978-3-031-03930-0

(eBook)

1st edition: © Ten Alps in 2020 in association with the Association of Optometrists 2nd edition: © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022, corrected publication 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Dedication This book is dedicated to the memory of Christine Fitzmaurice. For many years, Christine helped people with visual stress and then turned her boundless energies to advocating on behalf of all individuals with this condition. She organised conferences, research, publications, and most of all people. Her tireless work on the behalf of others in more need than herself is greatly missed.

v

Preface A paper in the British Medical Journal in 1896 by Morgan described a child with reading difficulty, referred to by Morgan as a case of ‘congenital word blindness’. Morgan thought that the eyesight was normal in this case, although only basic vision tests would have been possible at that time. Morgan thought the child "would be the smartest lad in the school if the instruction were entirely oral." This statement highlighted an obvious yet sometimes under-emphasised feature of reading difficulty: sufferers perform much worse when they are asked to read than when they are asked to listen. Since reading requires vision and listening does not it is perhaps surprising that most people with reading difficulty today are not routinely referred for an investigation of their visual function. There has been increasing evidence in recent years of visual factors playing a role in reading difficulties and the tide seems to at last be changing, with a growing number of teachers and parents involving eyecare practitioners when their children have difficulty reading. This book is aimed at providing these eyecare practitioners with a summary of the evidence concerning the visual conditions that they should search for, guidelines for diagnosis and, if necessary, treatment of these visual disorders. This book is written primarily for eyecare practitioners: optometrists, orthoptists, ophthalmologists, and opticians. The book is designed to be useful for any eyecare practitioner who may wish to help children or adults who experience reading difficulty, whether in primary, secondary, or tertiary care. The book also is intended to be useful for education professionals and parents, wishing to understand more about visual conditions that can co-occur with reading difficulties. vii

viii

Preface

The title of this book deliberately avoids the word dyslexia because the book is not just about dyslexia. Vision is a core component of the reading process. So, any person who has difficulty reading, or who reads competently but reluctantly, or who reads less accurately than would be expected from their other abilities, ought to consult an eyecare practitioner who has specialized in this field. This applies regardless of whether the person with reading difficulty meets the diagnostic criteria for dyslexia. The authors of this book have between them been researching the role of visual factors in reading difficulties for over 70 years. They come from psychology and optometry backgrounds and share a passion for removing visual obstacles to successful reading. The views expressed are solely those of the authors and represent an attempt to use scientific evidence to guide best practice in this controversial clinical field.

Acknowledgment The book is a substantial revision of an earlier book written with Professor Peter Allen. The authors thank Professor Allen for his contributions.

ix

Disclosures The Intuitive Overlays, Wilkins Rate of Reading Test, Intuitive Colorimeter and Precision Tinted lenses were invented by author AJW. AJW received an Award to Inventors from the Medical Research Council for the Rate of Reading Test and the Intuitive Colorimeter, based on a proportion of the royalties for these products. He has donated royalties from the latest version of the Intuitive Colorimeter (The Curve) to the University of Essex to fund student bursaries. BJWE invented the IFS system of eye exercises which are briefly mentioned in Chapter 3 and for which BJWE receives a royalty. The Intuitive Overlays, Wilkins Rate of Reading Test, Pattern Glare Test, and

IFS

exercises

are

available

from

i.o.o.

Sales

Ltd

(www.ioosales.co.uk). ioo sales is a company that raises funds for the Institute of Optometry, a charitable organisation. BJWE is Director of Research at the Institute of Optometry. The Intuitive Colorimeter and Precision Tinted Lenses are available from Cerium Visual Technologies (www.ceriumvistech.co.uk). AW and BE are committee members of the not-for-profit Society for Coloured Lens Prescribers (www.s4clp.org).

xi

Contents

Acknowledgment

ix

Disclosures

xi

1

Introduction

1

2

Refractive errors and ocular health

19

3

Binocular vision anomalies

37

4

Controversial vision therapies

73

5

Magnocellular theory

99

6

Coloured filters - early studies

143

7

Do coloured filters work?

169

8

How do coloured filters work?

195

9

Coloured filters as clinical tools

225

10

Clinical protocol

253

11

Other potential uses of precision tints

293

12

Research priorities and practice

323

Correction to: Vision, Reading Difficulties, and Visual Stress Appendices

C1 341

xiii

Chapter 1

Introduction

Chapter Abstract In this chapter the structure of the book is laid out, together with the underlying rationale. Types of learning difficulty and their relation to reading difficulties are described. The key visual deficits that can accompany reading difficulties – binocular instability and visual stress – are introduced. The associated symptoms and signs are described.

Introduction to the book This is a book of two parts. The first part (Chapters 2-5) discusses the visual factors that may be associated with difficulty reading and dyslexia. One of these factors, visual stress (which is alleviated with coloured filters), is covered in detail in the second part of the book (Chapters 6-12), which also covers the use of coloured filters in neurological disorders. There are several reasons why visual stress is covered in detail. First, it is believed to be a condition with a neurological basis, which co-occurs not just with reading difficulties but also with common neurological conditions (e.g., migraine, autism) and with other rarer, but important conditions (e.g., epilepsy, stroke, multiple sclerosis). Also, the authors are aware of a need for an up-todate review that brings together the research evidence, discusses the controversy surrounding visual stress, and summarises clinical guidelines. The authors’ goal is for this book to be accessible not only to eye © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 A. J. Wilkins and B. J. W. Evans, Vision, Reading Difficulties, and Visual Stress, https://doi.org/10.1007/978-3-031-03930-0_1

1

2

Chapter 1 - Introduction

care professionals and education professionals, but also to parents. Each section includes a lay description and there are frequent summaries in non-technical language. Scientific evidence is concisely reviewed with references to relevant literature, for those to wish to read further. In modern society most people are literate, and reading has become one of the most important tasks we do with our eyes. Nevertheless, references to reading difficulties can be traced back as far as the early seventeenth century when few of the population could read or needed to do so. Reading requires an individual to use their visual skills, phonetic ability (ability to analyse speech sounds) and knowledge of language to successfully recognize words and gather meaning from the written text. Given the complexity of the processes involved, it is unsurprising that there are many sources of reading difficulty. This book will concentrate on visual factors that can contribute to reading difficulties in people who do not have eye disease. There are several eye care professions. Optometry is the largest of these. The number of optometrists exceeds the sum of all the other eye care professionals. Most optometrists work in community optical practices and carry out eye examinations and sight tests. Optometrists have a statutory duty to diagnose and correct refractive errors (e.g., short-sightedness), orthoptic problems (difficulties with eye coordination), and some eye diseases. Some optometrists work in the hospital eye service and in research. In community practices, optometrists work alongside opticians (dispensing opticians), who are experts

on

spectacle

frames

and

lenses.

Optometrists

and

professionally qualified opticians in the UK must be registered with the General Optical Council and only registered opticians and optometrists can dispense spectacles to children. Ophthalmologists are medical

Chapter 1 - Introduction

3

professionals who have specialised in eyes. In the UK, nearly all ophthalmologists work in the hospital eye service where they treat eye disease, either with medicines or surgery. Orthoptists work mainly in the hospital eye service where they diagnose and treat eye coordination problems (e.g., strabismus). Many orthoptists are also involved in vision screening, which in the UK typically takes place once, shortly after school entry.1 Fewer than half of vision screening services in the UK are compliant with the relevant specifications, often lacking appropriate personnel or tests.2

Learning difficulties and reading Learning difficulties (disabilities) can be broadly classified into those that are developmental and those that are acquired. Developmental difficulties are much more common than acquired problems, which typically result from a neurological disorder. Visual stress can accompany

both

developmental

difficulties

and

neurological

disorders. Learning difficulties can also be classified into those that are general and those that are specific. Learning difficulties can affect a wide range of skills including general intelligence, as measured with an intelligence test, and expressed as an IQ. Specific learning difficulties (SpLD) only affect specific skills and can occur regardless of IQ.3 Chapters 1-5 of this book concentrate on SpLD. Since most learning is mediated by the written word, those with reading and spelling problems will struggle with education, even if they are intelligent and articulate. SpLD persist throughout life and can have deleterious consequences for careers.4 There are many types of SpLD.5 Some of the main ones are summarised below. x

Reading and spelling difficulties, dyslexia. The definition of dyslexia remains controversial,6 but a common definition is a learning

4

Chapter 1 - Introduction

difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling.4 Characteristic features of dyslexia are difficulties in phonological awareness (an understanding of the sound components of language), verbal memory, and verbal processing speed.4 Recent thinking on the causes of dyslexia are discussed at the end of Chapter 5. x

Difficulties with writing, dysgraphia. Dysgraphia can manifest as poor handwriting and trouble putting thoughts on paper.

x

Lack of numerical skill, dyscalculia.7 Dyscalculia refers to a wide range of life-long learning difficulties involving mathematics. There is no single form of maths disability, and difficulties vary from person to person and affect people differently in school and throughout life.

x

Difficulty with co-ordination, dyspraxia. This condition is closely related to conditions described by two other labels, developmental co-ordination disorder and clumsy child syndrome. The skills involved in writing, reading, listening, speaking, and

reasoning overlap and so it is not surprising that people can be diagnosed with more than one SpLD. Attention Deficit Hyperactivity Disorder (ADHD) is a condition that becomes apparent in some children in the preschool and early school years. ADHD is characterised by inattention and/or hyperactivity-impulsivity.8 ADHD is a common condition (although sometimes over-diagnosed)9 that is often associated with SpLD.10 ADHD is sometimes associated with hyperactivity (ADHD) but the condition can occur without hyperactivity, when the main features are inattention and impulsivity.

Chapter 1 - Introduction

5

Dyslexia in the late 1800’s dyslexia was called congenital word blindness.11 More recently, there has been an upsurge of interest in neurological factors affecting reading partly because of new and innovative imaging technology.12 Dyslexia is typically described as most common in males.13 Although some research suggests it is equally prevalent in both sexes,14 most research supports a greater prevalence in males attributed to hormone-related protective factors in females.15 Dyslexia often runs in families,16 and relevant genes have been identified.17 Dyslexia affects 5 to 17% of the school age population18 and can have a profound effect on schooling. The term dyslexia is sometimes used indiscriminately to refer to specific or even nonspecific learning difficulties. The causes of dyslexia are still debated19 although it is generally agreed that a core feature in many cases of dyslexia is a deficit in phonological abilities,20

a problem in

understanding the speech sound of words. But dyslexia, is more than just a phonological deficit and there is evidence that dyslexia is a multifactorial condition.21-23 Visual and language processing deficits often co-occur in dyslexia.24 The visual problems that are particularly prevalent are introduced below and discussed at greater length later in this book. Although these visual factors are not usually the main cause of dyslexia and are probably best considered as co-occurring factors, they can contribute to a child’s reading difficulties. In other words, in dyslexia the problem with reading and spelling can be due to many factors requiring a multidisciplinary approach to investigation and treatment. An eye care practitioner is one member of this multidisciplinary team.

6

Chapter 1 - Introduction

There have been many attempts over the years to classify dyslexia into subtypes.25 Typically, these classifications include three groups: an auditory or phonological subtype (dysphonetic), a visual-spatial or performance

group

(dyseidectic),

and

a

mixed

group

(dysphonetic/dyseidectic); although other classifications have also been suggested.26 The classifications are controversial: some studies suggest that dyslexia is so heterogeneous that it defies classification. 27 It should be stressed that the visual-spatial subgroup have difficulties with high level visual functions, not with the low level visual functions that eye care practitioners assess. In fact, such classifications are not useful as indicators of which cases should see an eye care practitioner.28 Current thinking has developed beyond the concept of sub-types and unitary causes of dyslexia and instead considers dyslexia as a multifactorial condition, best considered with respect to “an additive risk factor model”.21 The evidence for this model and its implications are considered further at the end of Chapter 5. It is the eye care practitioner’s role to provide appropriate investigation and management of visual factor(s) that may contribute to the difficulty reading.29 Diagnosis of dyslexia is not the role of an eye care practitioner but that of an educational psychologist or teacher qualified in special educational needs. The diagnosis of dyslexia is usually one of exclusion, following specific educational tests, after other factors such as intellectual disability and gross dysfunctions of hearing or vision have been ruled out. Of course, a person does not need to have been diagnosed as dyslexic before seeking help from an optometrist. Indeed, it would seem sensible for any children whose teachers or parents suspect underachievement at school to, at an early stage, have a detailed investigation with an eye care practitioner who has specialised in vision and learning.

Chapter 1 - Introduction

7

Key clinical visual correlates of reading difficulties The visual correlates of reading difficulties are discussed in detail in this book and will now, by way of an introduction, be briefly reviewed. Throughout this book, priority is given to evidence-based research. As noted in Chapter 11, this means that emphasis is placed on visual factors that have been shown to be associated with reading difficulties either in matched group studies or correlational studies. Treatments or interventions are only included in this book if they are supported by research evidence, ideally randomised controlled trials. Even if a visual condition is not, in general, associated with dyslexia, the visual condition could still contribute to difficulties with reading in individual cases. This is illustrated in case study 1.1.

Case study 1.1 A 29 year old lady consulted an optometrist for her first eye examination. She had underachieved at school and was now engaging in adult education, leading to referral to an educational psychologist. The psychologist had diagnosed dyslexia and, noting visual symptoms, suspected visual stress. Symptoms included text blurring and eyestrain. Examination at presentation revealed reduced visual acuities and a significant degree (three dioptres in the right eye; four dioptres in the left eye) of myopic astigmatism. All other optometric test results were normal. Spectacles were prescribed and with these, the symptoms fully resolved.

8

Chapter 1 - Introduction

In Chapters 2-5, the visual conditions that are discussed will be considered under five headings that conform to the precepts outlined earlier: x

Background

x

Is the visual condition associated with reading difficulty?

x

Is there evidence of the visual condition contributing in a causal way to reading difficulty?

x

How is the visual condition detected?

x

How is the visual condition treated?

Binocular instability Binocular instability (Chapter 3) describes a subtle problem in coordinating the two eyes together. In the clinic, binocular instability is detected as an unstable heterophoria and low fusional reserves (for description see Chapter 3). A controlled study found that the main sign of binocular instability (low fusional reserves) is present in about 5% of good readers and in 15% of poor readers.30 This does not mean that 15% of poor readers need optometric treatment because binocular instability may in some cases be subtle and may not require treatment if it is not causing symptoms.31 The fact that 5% of good readers have one of the signs of binocular instability shows that there is not a simple causal relationship between fusional reserves and reading ability: low fusional reserves will not necessarily make a person a poor reader.

Visual Stress Visual Stress is sometimes called Meares-Irlen Syndrome in recognition of the two individuals who first described the use of coloured filters as a treatment for people who experience discomfort

Chapter 1 - Introduction

9

and perceptual distortions on viewing text. The term coloured filters is used generically to describe both coloured overlays (transparent plastic sheets placed on the page) and coloured lenses. Visual stress is arguably a form of photophobia, characterised by symptoms of perceptual distortion and discomfort when viewing certain spatially repetitive stimuli, typically text. The symptoms can often be alleviated using coloured filters of a specific individually chosen colour.32 The condition appears to have a greater prevalence in individuals who suffer from dyslexia,33 chronic

fatigue

syndrome

(myalgic

34

migraine,35-37 autism,38-40

encephalitis),41-43

multiple

sclerosis,44 stroke,45-47 head injury48 and photosensitive epilepsy.49-51 In susceptible individuals, symptoms of visual stress are likely to occur when the visual scene contains elements of a high contrast configurations of stripes (Figure 1.1).52-55 Visual stress is believed to be a condition separate from dyslexia, but the two conditions can cooccur.4 33 34 Reading material (which has stripes from horizontal lines and from vertical letter strokes) has the potential to elicit visual stress.56

57

A

condition that would nowadays be called visual stress was described by Critchley (1964),58 Meares (1980)59, Irlen (1983)60 and Wilkins (1984).61 The susceptibility of some individuals to reading-related visual stress has been variously termed scotopic sensitivity syndrome, Irlen syndrome, Meares-Irlen syndrome (MIS),62 pattern-related visual stress (PRVS),54 Meares-Irlen syndrome/visual stress (MISViS)63, and sensory visual stress.31 The history of this condition is described in Chapter 6. Wilkins has proposed that the underlying anomaly in visual stress is a hyper-excitability of the visual cortex, possibly as a result of impaired gain control mechanisms, and that the effects of this can be alleviated in a variety of ways, including modifying the design and layout of printed text and through the use of colour.53

61

Although there is

10

Chapter 1 - Introduction

considerable evidence for the existence of visual stress, the condition remains controversial (discussed later in this book). In particular, the exact mechanism is still debated and under investigation.

Figure 1.1. The pattern glare test, described in Chapter 10. The prevalence of visual stress depends on the diagnostic criteria used but significant degrees of visual stress is likely to affect fewer than one in five people with dyslexia.64 65 Adults with dyslexia are also more likely to have visual stress than adults who are good readers, and the combination of dyslexia and visual stress adversely affects reading speed.34 Visual stress, together with the various approaches to the correction of the condition using coloured filters, are discussed in Chapters 6-8.

Chapter 1 - Introduction

Visual

11

symptoms

in

people

with

reading

difficulties Eye care practitioners are in an ideal position to screen for people who may be experiencing reading difficulties by asking a few key questions when taking a patient’s symptoms and history. Parents of children who have trouble learning to read often seek help from a teacher and/or an educational psychologist. Teachers and educational psychologists may recommend that the child consults an eye care practitioner who has specialised in vision and learning. Since reading involves vision, it is perhaps surprising that such a recommendation is not made more often. A visual problem is particularly likely to be present in a person who has trouble learning to read if they report headaches and eye-strain after reading. The symptoms that are associated with the most relevant visual problems (e.g., visual stress, binocular instability) typically develop after a period of reading, and visual stress tends to be more common when viewing many lines of text in smaller fonts. This means that these visual problems may produce more symptoms in older children, who are “reading to learn”, rather than in younger children, who are “learning to read”. It is recommended that eye care practitioners ask, "After you have been reading for a while, do the words or letters do anything different?”

Suspicious

symptoms

are

graphically

illustrated

at

www.opticalm.ca, and can include: x

Letters appearing to move – this can appear in many forms including the words moving up and down, side to side, words merging, words breaking up and words moving.

x

Letters appearing to blur especially with closely spaced small print

12

Chapter 1 - Introduction

x

Letters appearing double

x

Letters changing size

x

Letters changing contrast

x

Letter or word reversals

x

Colours or shapes appearing on the page

x

Text appearing to flicker

x

Discomfort under fluorescent lights and some LEDs

x

The occurrence of headaches, nausea or dizziness

x

Eyes becoming tired or sore

x

The page appearing too bright

Symptoms are discussed in more detail in Chapter 10, which includes a more extensive list of symptoms and the conditions that are likely to cause these symptoms (Table 10.1). The practitioner should be aware of the limitations in the use of symptoms as a diagnostic tool. The recall of symptoms is prone to bias; memory processes have been shown to be biased by mood, emotion and many other factors.66 Recall of symptoms may vary and can depend on factors such as the mood at testing. Intermittent problems might be specific to certain environmental factors such as lighting or a particular task. Also, people often fail to recognise significant symptoms until the symptoms have been removed – they consider what they are experiencing to be normal. As illustrated in Table 10.1, most symptoms are non-specific: it is not possible to diagnose a visual problem with certainty from symptoms alone. In addition to symptoms, the parent or teacher may observe behaviours or signs which alert the practitioner to the possibility of visual problems. Suspicious signs when reading include the following:

Chapter 1 - Introduction

13

x

Wearing spectacle lenses with tints or sunglasses when reading

x

Rubbing eyes

x

Excessive blinking

x

Tracking the text with a finger due to difficulties in keeping place (Figure 1.5a)

x

Closing or covering one eye (Figure 1.5b)

x

Moving unusually close or far away from text

x

Poor concentration which might be indicated by yawning, frequently looking away from the page and fidgeting

x

Poor reading fluency that slows the longer the person reads

The number of signs and symptoms experienced by the person can give an indication of the severity of their susceptibility to visual stress. The reporting of symptoms provides a useful indication that an individual may warrant further investigation, as discussed in later chapters. Symptoms are more reliable when a person is asked about their symptoms whilst they are viewing text than when they are asked to recollect their symptoms.66 Some teachers use checklists including the symptoms and signs listed above to indicate the presence of visual stress. However, these symptoms and signs can also be caused by a variety of conditions such as uncorrected refractive error (requiring glasses or contact lenses), accommodation (a focussing weakness) and/or binocular vision (eye coordination) problems, in addition to or independently of visual stress. The authors have always advocated that people with reading difficulties should have a full visual investigation by an eye care practitioner who has specialised in vision and learning (see Chapter 10). Research in recent years has helped to outline the protocol for these investigations and this will be described in Chapter 10.

14

Chapter 1 - Introduction

References 1. Emond A, Adams C, Barlow J, et al. G354(P) Health for all children 5: a comprehensive critical review of evidence supporting child health programmes. Archives of Disease in Childhood 2019;104(Suppl 2):A145-A45. doi: 10.1136/archdischild-2019-rcpch.342 2. British and Irish Orthoptic Society, Clinical Council for Eye Health Commissioning. Vision screening provision in children aged 4-5 years in England: Findings from a Freedom of Information Request 2019. https://www.orthoptics.org.uk/wp-content/uploads/2020/03/2019-VS-FOIReport-March-2020.pdf, 2020. 3. Ferrer E, Shaywitz BA, Holahan JM, et al. Uncoupling of reading and IQ over time: empirical evidence for a definition of dyslexia. Psychol Sci 2010;21(1):93-101. doi: 0956797609354084 [pii];10.1177/0956797609354084 [doi] 4. Rose J. Identifying and teaching children and young people with dyslexia and literacy difficulties. Department for Education, 2009. 5. World Health Organization. International classification of diseaes for mortality and morbidity statistics: World Health Organization; 2018 [updated 17/12/2020. Eleventh:[Classification]. Available from: https://icd.who.int/browse11 accessed 22/03/2021 2021. 6. Snowling MJ, Hulme C, Nation K. Defining and understanding dyslexia: past, present and future. Oxf Rev Educ 2020;46(4):501-13. doi: 10.1080/03054985.2020.1765756 [published Online First: 2020/09/18] 7. Shalev RS, Gross-Tsur V. Developmental dyscalculia. Pediatr Neurol 2001;24(5):337-42. 8. World Health Organization. International Statistical Classification of Diseases and Related Health Problems (ICD-11), 2021. 9. Kazda L, Bell K, Thomas R, et al. Overdiagnosis of AttentionDeficit/Hyperactivity Disorder in Children and Adolescents: A Systematic Scoping Review. JAMA Netw Open 2021;4(4):e215335. doi: 10.1001/jamanetworkopen.2021.5335 [published Online First: 2021/04/13] 10. McDougal E, Gracie H, Oldridge J, et al. Relationships between cognition and literacy in children with attention-deficit/hyperactivity disorder: A systematic review and meta-analysis. Br J Dev Psychol 2021 doi: 10.1111/bjdp.12395 [published Online First: 2021/10/05] 11. Morgan P. A case of congenital word blindness. Br Med J 1896;Nov 7:1378. 12. Finn ES, Shen X, Holahan JM, et al. Disruption of functional networks in dyslexia: a whole-brain, data-driven analysis of connectivity. Biol Psychiatry 2014;76(5):397-404. doi: 10.1016/j.biopsych.2013.08.031 [published Online First: 2013/10/16] 13. Liederman J, Kantrowitz L, Flannery K. Male vulnerability to reading disability is not likely to be a myth: a call for new data. J Learn Disabil

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2005;38(2):109-29. doi: 10.1177/00222194050380020201 [published Online First: 2005/04/09] 14. Shaywitz SE, Shaywitz JE, Shaywitz BA. Dyslexia in the 21st century. Curr Opin Psychiatry 2021;34(2):80-86. doi: 10.1097/YCO.0000000000000670 [published Online First: 2020/12/06] 15. Granocchio E, De Salvatore M, Bonanomi E, et al. Sex-related differences in reading achievement. J Neurosci Res 2021 doi: 10.1002/jnr.24913 [published Online First: 2021/07/10] 16. Rack JP. The biological bases of reading ability: (1) Evidence from behaviourgenetic studies. Dyslexia Review 1995:7-11. 17. Thambirajah MS. Developmental dyslexia: an overview. Advances in Psychiatric Treatment 2010;16(4):299-307. doi: 10.1192/apt.bp.108.006072 18. Habib M, Giraud K. Dyslexia. Handb Clin Neurol 2013;111:229-35. doi: 10.1016/B978-0-444-52891-9.00023-3 [published Online First: 2013/04/30] 19. Smythe I. Dyslexia. Br J Hosp Med (Lond) 2011;72(1):39-43. doi: 10.12968/hmed.2011.72.1.39 [published Online First: 2011/01/18] 20. Saksida A, Iannuzzi S, Bogliotti C, et al. Phonological skills, visual attention span, and visual stress in developmental dyslexia. Dev Psychol 2016;52(10):1503-16. doi: 10.1037/dev0000184 21. O'Brien G, Yeatman JD. Bridging sensory and language theories of dyslexia: Toward a multifactorial model. Dev Sci 2020:e13039. doi: 10.1111/desc.13039 [published Online First: 2020/10/07] 22. Slaghuis WL, Lovegrove WJ, Davidson JA. Visual and language processing deficits are concurrent in dyslexia. Cortex 1993;29:601-15. 23. van der Kleij SW, Segers E, Groen MA, et al. Post-treatment reading development in children with dyslexia: the challenge remains. Ann Dyslexia 2019;69(3):279-96. doi: 10.1007/s11881-019-00186-6 [published Online First: 2019/10/17] 24. Ramus F, Rosen S, Dakin SC, et al. Theories of developmental dyslexia: insights from a multiple case study of dyslexic adults. Brain 2003;126(4):841-65. 25. Boder, E. Developmental dyslexia: A diagnostic approach. Dev Med Child Neurol 1973;15:663-87. 26. Watson C, Willows DM. Information-processing patterns in specific reading disability. J Learn Disabil 1995;28(4):216-31. 27. Brown GDA. Cognitive analysis of dyslexia. Perception 1988;17:695-98. 28. Evans BJW. Dyslexia and Vision. Chichester: Wiley 2001. 29. Evans BJW. Guest editorial. Do visual problems cause dyslexia? Ophthal Physiol Opt 1999;19(4):277-78. 30. Evans BJW, Drasdo N, Richards IL. Investigation of accommodative and binocular function in dyslexia. Ophthal Physiol Opt 1994;14(1):5-19. 31. Evans BJW. Pickwell's Binocular Vision Anomalies. Sixth ed. Philadelphia: Elsevier 2021. 32. Millodot M. Dictionary of Optometry. Seventh ed. Oxford: ButterworthHeinemann 2009.

16

Chapter 1 - Introduction

33. Kriss I, Evans BJW. The relationship between dyslexia and Meares-Irlen Syndrome. J Res Reading 2005;28(3):350-64. 34. Singleton C, Trotter S. Visual stress in adults with and without dyslexia. Journal of Research in Reading 2005;28(3):365-78. 35. Marcus DA, Soso MJ. Migraine and stripe-induced visual discomfort. Arch Neurol 1989;46:1129-32. 36. Harle DE, Shepherd AJ, Evans BJ. Visual stimuli are common triggers of migraine and are associated with pattern glare. Headache 2006;46(9):143140. 37. Vieira A, van der Linde I, Bright P, et al. Preference for Lighting Chromaticity in Migraine With Aura. Headache 2020;60(6):1124-31. doi: 10.1111/head.13801 [published Online First: 2020/04/14] 38. Ludlow AK, Wilkins AJ. Atypical Sensory behaviours in children with Tourette's Syndrome and in children with Autism Spectrum Disorders. Res Dev Disabil 2016;56:108-16. doi: 10.1016/j.ridd.2016.05.019 39. Whitaker L, Jones CR, Wilkins AJ, et al. Judging the Intensity of Emotional Expression in Faces: the Effects of Colored Tints on Individuals With Autism Spectrum Disorder. Autism Res 2016;9(4):450-9. doi: 10.1002/aur.1506 40. Ludlow AK, Wilkins AJ, Heaton P. Colored overlays enhance visual perceptual performance in children with autism spectrum disorders. Research in Autism Spectrum Disorders 2008;2(3):498-515. 41. Wilson RL, Paterson KB, Hutchinson CV. Increased Vulnerability to PatternRelated Visual Stress in Myalgic Encephalomyelitis. Perception 2015;44(12):1422-6. doi: 10.1177/0301006615614467 42. Loew SJ, Marsh NV, Watson K. Symptoms of Meares-Irlen/Visual Stress Syndrome in subjects diagnosed with Chronic Fatigue Syndrome. International Journal of Clinical Health & Psychology 2014;14(2):87-92. 43. Smith AP, Behan PO, Bell W, et al. Behavioural problems associated with the chronic fatigue syndrome. Br J Psychol 1993;84 ( Pt 3):411-23. 44. Newman WB, Wilkins AJ, Zoukos Y. Spectral filters can improve reading and visual search in patients with multiple sclerosis. J Neurol 2007;254(12):1729-35. 45. Beasley IG, Davies LN. The effect of spectral filters on reading speed and accuracy following stroke. Journal of Optometry 2013;06(03):134-40. 46. Beasley IG, Davies LN. Susceptibility to pattern glare following stroke. J Neurol 2012 doi: 10.1007/s00415-012-6418-5 [doi] 47. Beasley IG, Davies LN. Visual stress symptoms secondary to stroke alleviated with spectral filters and precision tinted ophthalmic lenses: a case report. Clin Exp Optom 2012 doi: 10.1007/s00415-012-6418-5 [doi] 48. Fimreite V, Willeford KT, Ciuffreda KJ. Effect of chromatic filters on visual performance in individuals with mild traumatic brain injury (mTBI): A pilot study. J Optom 2016 doi: 10.1016/j.optom.2016.04.004 49. Wilkins AJ, Binnie CD, Darby CE, et al. Inferences regarding the visual precipitation of seizures, eye strain, and headaches. In. Generalised Epilepsy: Neurological Approaches 1990:Eds.

References

17

50. Wilkins AJ, Binnie CD, Darby CE. Visually-induced seizures. Prog In Neurobiol 1980;15:85-117. 51. Wilkins AJ, Darby CE, Binnie CD. Neurophysiological aspects of patternsensitive epilepsy. Brain 1979;102:1-25. 52. Wilkins A. Reading and visual discomfort. In: Willows DM, Kruk RS, Corcos E, eds. Visual Process in Reading and Reading Disabilities. First ed. Hillsdale, New Jersey: Lawrence Erlbaum Associates 1993:435-56. 53. Wilkins A. Visual stress: origins and treatment. CNS 2021;6:1-13. 54. Allen PM, Gilchrist JM, Hollis J. Use of visual search in the assessment of pattern-related visual stress (PRVS) and its alleviation by coloured filters. Invest Ophthalmol Vis Sci 2008 55. Evans BJW, Cook A, Richards IL, et al. Effect of pattern glare and colored overlays on a simulated-reading task in dyslexics and normal readers. Optom Vis Sci 1994;71(10):619-28. 56. Wilkins A. Visual discomfort and reading. In. Vision and Visual Dysfunction 1991;Vol. 13:ed. 57. Wilkins AJ, Nimmo-Smith I. On the reduction of eyestrain when reading. Ophthal Physiol Opt 1984;4(1):53-59. 58. Critchley M. Developmental dyslexia. London: Whitefriars Press 1964. 59. Meares O. Figure-ground, brightness contrast and reading disabilities, 1980. 60. Irlen H. Successful treatment of learning difficulties. Paper presented at Annual Convention of the American Psychological Association, Anaheim, California 1983 61. Wilkins A, Nimmo-Smith I, Tait A, et al. A neurological basis for visual discomfort. Brain 1984;107:989-1017. 62. Evans BJW. Coloured filters and dyslexia: what's in a name? Dyslexia Review 1997;9(2):18-19. 63. Evans B. Coloured filters and other co-occurring visual factors in dyslexia. In: Stein J, ed. Dyslexia and Co-occurring difficulties. First ed. Bracknell: British Dyslexia Association 2012:25-46. 64. Evans BJW, Allen PM, Wilkins AJ. A Delphi study to develop practical diagnostic guidelines for visual stress (pattern-related visual stress). Journal of Optometry 2017;10(3):161-68. 65. Evans BJW, Allen PM. A systematic review of controlled trials on visual stress using Intuitive Overlays or the Intuitive Colorimeter. Journal of Optometry 2016;9(4):205-18. 66. Hollis J, Allen PM. Screening for Meares-Irlen sensitivity in adults: can assessment methods predict changes in reading speed? Ophthalmic Physiol Opt 2006;26(6):566-71.

Chapter 2 Refractive errors & ocular health

Chapter Abstract The components of a clinical optometric examination are explained, and how they relate to ocular health, visual fields, colour vision and refractive error. The possible associations with reading difficulty and techniques for treatment are set out. It is concluded that refractive errors, visual acuity, and ocular pathology are not correlates of developmental reading difficulties. However, refractive errors are common and can affect the ability to resolve detail, and therefore can contribute to reading difficulties in some cases.

Ocular health Thankfully, eye diseases are rare in childhood. Certain pathologies can, however, significantly reduce a child’s visual acuity although such reduced acuity does not necessarily affect reading under optimal conditions.1 Eye disease is not more common in children with reading difficulties,2 3 but can occur in any child and an examination of ocular health is an essential part of any eye examination. Eye disease become increasingly prevalent with age, and this can cause reduced visual acuity and/or restricted visual fields, which can impair reading. This acquired reading difficulty is very different to the developmental reading difficulty that is present in dyslexia.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 A. J. Wilkins and B. J. W. Evans, Vision, Reading Difficulties, and Visual Stress, https://doi.org/10.1007/978-3-031-03930-0_2

19

20

Chapter 2 - Refractive errors & ocular health

Visual fields Eye care practitioners often perform an assessment of visual fields using automated perimeters. These perimeters may be insensitive to some of the subtle visual field asymmetries that have been reported as correlates of reading difficulties (dyslexia), which are discussed in Chapter 5. In laboratory-based studies there is a continuing debate as to whether people with reading difficulties show visual field (left/right) asymmetries on verbal or visual spatial tasks4-6 (Chapter 5). Some researchers have found that in certain tasks individuals with dyslexia show a statistically significant right-sided bias7 leading to descriptions of “mini-neglect” of the left visual field in poor readers;8 although this was not found in a line bisection task.9 In any event, visual neglect is quite different to a visual field defect (subtle or otherwise) and there is no good evidence that clinically abnormal visual fields are a significant factor in reading difficulties. In recent years, a new method of perimetry has become popular for detecting glaucoma. It uses a frequency doubling technique (FDT) that is believed to detect the magnocellular deficit in glaucoma (see Chapter 5). It has been shown that the test can also detect a magnocellular deficit in dyslexia.10 The deficit is subtle and is not likely to interfere with the clinical use of FDT to detect glaucoma,11 which is extremely rare in childhood.

Chapter 2 - Refractive errors & ocular health

21

Figure 2.1. Frequency doubling technique for visual field testing Occasionally, patients can acquire reading difficulties, usually abruptly, as a sign of neurological disease (e.g., stroke). Clinicians should be alert to the possibility of these rare cases, which require prompt neurological investigation. Although most reading difficulties are not due to neurological disease, routine visual field testing is a sensible precaution in children who are able to perform the test as it will help to detect some of these rare cases, when the aetiology is not apparent from the history.

Colour vision anomalies In schools, colour is used extensively for teaching and many vocations and hobbies require some degree of colour identification. Approximately one in 12 men and one in 200 women have a congenital colour vision deficiency. This is sometimes called “colour blindness”, although this term is deprecated because people with colour vision

22

Chapter 2 - Refractive errors & ocular health

anomalies can discriminate many colours, even though the range of colour discrimination is reduced. True colour blindness is extremely rare and caused by eye diseases. Distinct from congenital colour vision deficiencies, some people develop acquired colour vision deficiency, typically as a result of pathology or medications. The incidence of acquired colour vision deficiencies increases with age. Colour vision defects do not seem to be correlated with dyslexia, 3 or visual stress.12

13

However, the number of non-specific colour

confusions appears to be unexpectedly high in SpLD.14

15

This may

result from the use of pseudoisochromatic plates, illustrated in Figure 2.2.16 The authors have encountered people with severe visual stress who have had specific difficulties with the Ishihara test, although their colour perception on other colour vision tests is normal. It seems that the visual stress causes difficulties in perceiving figures in visual noise, possibly

exacerbated

by

strong

colour

contrasts

in

pseudoisochromatic plates. This effect has not been formally investigated so this anecdotal observation should be interpreted with caution.

Chapter 2 - Refractive errors & ocular health

23

Figure 2.2. The Ishihara pseudoisochromatic colour test

Visual Acuity Visual acuity is tested with a letter chart (Figure 2.3) and such charts are now typically computerised, allowing the letters to be randomised so they cannot be memorised. Visual acuity is most often measured for distance vision (e.g., 6 m), but can be measured at any distance. Print sizes that are typically used in text, especially for children, are much larger than the limit of visual acuity and reduced visual acuity is rare in children. This may explain why most studies have not found an association between reduced visual acuity and reading difficulties, or specifically with dyslexia.1 17 It is unfortunate that the test of visual performance that is typically used in vision screening in young children (visual acuity) does not

24

Chapter 2 - Refractive errors & ocular health

assess visual performance at near, which is where children undertake most of their reading.18 Parents sometimes assume that vision screening replaces the need for professional eye care, despite the fact that children’s vision is only screened once, and typically at an age before many refractive errors develop.19

Figure 2.3. A letter chart used for testing visual acuity. Reproduced with permission from Bailey and Lovie (1976).20 Occasionally, patients with severe visual stress are encountered where visual acuity seems to be reduced by several lines, improving to normal with individually prescribed coloured filters. These cases appear to be rare and have not been formally studied, so it is not possible to be sure whether these visual symptoms are psychogenic (a

Chapter 2 - Refractive errors & ocular health

25

so-called visual conversion reaction).21 Recently, however, Veszeli and Shepherd reported that more than one third of a sample of school children from East London improved their near visual acuity with an overlay of their preferred colour.22 The mean improvement was about one line and this finding has not yet been formally explored.

Refractive error Background The eyes contain lenses that focus light onto the retinae at the back of the eyes. Vision is blurred if the lenses do not focus correctly. If the lenses of the eye are too weak, objects near to the person will be more blurred than objects in the distance and the eye is long-sighted (hypermetropic). If the lenses of the eye are too strong, objects far away will be more blurred than objects close to; the eye is short-sighted (myopic). Long- and short-sightedness are refractive errors. When there is no refractive error, and the eyes are perfectly in focus, the eyes are said to be emmetropic. Hypermetropia is corrected with convex (plus) lenses and myopia with concave (minus) lenses. Anisometropia occurs when the refractive error in one eye is markedly different from that in the other eye. In an ideal world, the eyeball should be perfectly spherical (round, like a football). In the real world, it is often not precisely spherical, but is shaped a little more like a rugby ball. This causes another type of refractive error, astigmatism. The lens inside the eye can vary its focus. This allows a normal eye to change focus (accommodate) from the relaxed state, when it is focussed for distance vision, to an accommodated state, for near vision. The lens loses its ability to focus with age, which is why most people in their mid-forties start to need reading glasses.

26

Chapter 2 - Refractive errors & ocular health

When a young person views objects close to, such as a book, the eyes not only accommodate, but also turn inwards (converge) to align on the object (Chapter 3). The accommodation and convergence are linked, so that for a given amount of accommodation the eyes usually converge to a predictable degree. This can be a problem for children with long-sightedness who may use accommodation to compensate for long-sightedness, causing them to over-converge. This is a common cause of an eye turning inwards (convergent strabismus). In other words, refractive errors can cause problems with eye alignment, resulting in binocular vision anomalies.23 Binocular vision anomalies, and their relationship with reading difficulties, are discussed further in Chapter 3.

Are refractive errors associated with reading difficulty? Induced blur causes a reduced accuracy and rate of reading.24 Myopia, astigmatism and anisometropia do not seem to have an atypical prevalence in patients with reading difficulties,3 17 and the rest of this section will concentrate on hypermetropia. Interestingly, there is some evidence for a weak correlation between myopia and superior intelligence.25

26

In recent years, the prevalence of myopia has

increased markedly. In East Asia, nearly all university students are myopic. In the UK, just over half of university students are myopic, and the prevalence is increasing.27 Significant myopia will cause blurred distance vision, impairing a child’s ability to read the white board in class. Myopia is very unlikely to be present in the early school years, when vision screening takes place. Also, children may not report blurred distance vision, because it develops gradually. This is one reason why all children should have regular eye examinations. In children, there is a weak association between hypermetropia and

Chapter 2 - Refractive errors & ocular health

27

impaired visual perceptual skills28 and reading difficulties.26 The relationship with reading persists after adjustment for differences in intelligence, sex, and socioeconomic group. 26 A large multi-centre study of pre-school children found that uncorrected hypermetropia is associated with lower levels of literacy, although this study did not control for IQ.29 A similar finding in a study of secondary school children,30 is also difficult to interpret because the study did not control for IQ.26 Since these studies of the general population show a weak association between hypermetropia and reading difficulties, it is perhaps surprising that hypermetropia does not seem to be more likely to occur in dyslexia than in normal readers.2

3

In any event,

hypermetropia is so common that it is often found in any cross-section of children, including those with dyslexia.

Do refractive errors contribute (causally) to reading difficulty? In children, the association between hypermetropia and reading difficulty does not necessarily indicate a causal relationship. However, hypermetropia is also associated with poorer visual perceptual skills than myopia or emmetropia,31 and this can be improved with early correction of the hypermetropia.32 33 This supports the view that, at least in some cases, hypermetropia can be a cause of reading difficulty. In young adults, the routine correction of low degrees of hypermetropia does not have a significant effect on reading speed34, but may have an effect when symptoms are present.35 In older adults (over the age of 35 years), when the eyes are losing the ability to accommodate, reading glasses significantly improve the speed of reading.34 This is not linked to dyslexia, but a part of the ageing process that will affect everyone, unless they are short-sighted.

28

Chapter 2 - Refractive errors & ocular health

How are refractive errors detected? Visual acuity tests are useful to detect myopia, but are not reliable for detecting hypermetropia or astigmatism in children. 30 36 Typically, vision screening only tests visual acuity and this is another reason why children should have regular eye examinations.30 Although refractive errors are not strongly correlated with reading difficulties, eye care practitioners will occasionally encounter cases of suspected reading difficulties or dyslexia who turn out simply to have uncorrected refractive errors. For example, astigmatism is an optical error of the eye which Case study 2.1 A 29 years-old lady consulted an optometrist for her first eye examination. She had underachieved at school and was now engaging in adult education, leading to referral to an educational psychologist. The psychologist had diagnosed dyslexia and, noting visual symptoms, the psychologist suspected visual stress. Symptoms included text blurring and eyestrain. Examination at presentation revealed reduced visual acuities and a significant degree (three dioptres in the right eye; four dioptres in the left eye) of myopic astigmatism. All other optometric test results were normal. Spectacles were prescribed and with these, the symptoms fully resolved. On questioning, the lady had never undergone an eye examination or vision screening, and thought her vision had been the same all her life.

Chapter 2 - Refractive errors & ocular health

29

requires correction by spectacles or contact lenses. High uncorrected astigmatism is not strongly correlated with reading difficulty. This statement means that research studies that have compared a group of dyslexic children with a group of good readers do not find more astigmatism in the dyslexic group. However, anyone can have astigmatism and if this is present and not corrected it can make reading more difficult for any child, whether dyslexic or not. A child presenting with uncorrected astigmatism could be misdiagnosed as having dyslexia, when in fact their difficulty is attributable to the astigmatism alone.37 Case study 2.1 illustrates a case who may have been misdiagnosed as having a learning difficulty when the underachievement was attributable, at least in part, to uncorrected astigmatism. Case study 2.1 is an example of a missed refractive error. When the astigmatism was corrected, the reading skills rapidly improved. Therefore, it seems possible the person was mis-diagnosed with dyslexia. Eye care practitioners who specialise in vision and learning will also encounter another type of case, perhaps more commonly, where visual stress is misdiagnosed as refractive error. Case study 2.2 is a person who had visual stress misdiagnosed as uncorrected refractive error Case study 2.2 Background

ƒ 10 years-old boy referred to one of the authors because of specific learning difficulties.

Symptoms

ƒ With books and the white-board: text initially clear, then blurs, moves, and doubles and causes sore & tired eyes. Tends to skip words when reading

30

History

Chapter 2 - Refractive errors & ocular health

ƒ Reported these symptoms to an optometrist about a year ago who prescribed spectacles with a low/insignificant correction for longsightedness (R=L=+0.50DS) ƒ Patient and parents report the glasses were no help and were soon discarded

Presenting vision

ƒ R6/6+ L6/6 (normal in each eye)

Refractive

ƒ Retinoscopy: R+0.25DS L plano

error

ƒ Subjective: R=L= plano (normal)

Ocular

ƒ Ophthalmoscopy, visual fields, pupil reactions, colour vision (Ishihara) all normal

health

ƒ Cover test: D orthophoria N 2' XOP Ocular motor balance

ƒ Convergence, accommodation, fusional reserves, AC/A, stereopsis all normal, no fixation disparity at D or N ƒ MEM: R=L=+0.50DS ƒ (eye alignment & focussing normal)

Chapter 2 - Refractive errors & ocular health

31

ƒ Pattern glare test: positive response to Pattern 2 ƒ When viewing text patient reports that it blurs, moves, & eyes hurt. +0.50DS R&L has no effect on these symptoms.

Visual stress

ƒ Consistent response to testing with Intuitive Overlays, reporting that mint-green overlay eliminates the above symptoms ƒ Issued with mint-green overlay to try ƒ Returns after 1 month reporting that parents, teacher, and child have noticed improvement ƒ Consistent response to testing with Intuitive Colorimeter & Precision Tinted Lenses (as explained later in this book, these results indicate visual stress was present)

Management

Follow-up

ƒ Prescribed Precision Tinted lenses to use for class, homework, reading ƒ Parents & teachers report improvement ƒ Child reports precision tints alleviate symptoms

R, right; L, left; DS, dioptres spherical; D, distance; N, near; MEM, monocular estimate method of testing accommodative lag.

Cases like that in Case study 2.2 are perhaps not surprising. When eye care practitioners who are not familiar with visual stress encounter a patient reporting blurred vision during reading it is understandable that the practitioner suspects refractive error. If the practitioner encounters a normal degree of hypermetropia, they may be tempted to try a refractive correction in the hope of alleviating blurring, even though the low level of hypermetropia would not normally cause blur. The normal result for tests of accommodation and binocular vision (Chapter 3) in this case indicates that such a correction is unlikely to be

32

Chapter 2 - Refractive errors & ocular health

helpful and this was the patient’s experience. Testing with coloured overlays revealed a colour that eliminated the symptoms, and subsequent tests and feedback indicate that visual stress is the most likely cause of the blurring in this case. Visual stress is explained further in Chapters 6-11.

How are refractive errors corrected? There is considerable debate as to when hypermetropia should be corrected with spectacles.28

38-42

It is important to take account of

symptoms and, in view of the relationship between eye alignment and refractive error, practitioners should consider tests of eye alignment (binocular coordination) and accommodation (Chapter 3) when deciding whether to prescribe.23 Some optometrists argue that children with SpLD routinely should be prescribed low power convex (low plus) lenses (e.g., R=L=+0.50DS), sometimes euphemistically called ‘reading lenses’. A review found no convincing

experimental

prescriptions.

43

evidence

of

a

benefit

from

such

The College of Optometrists in the UK have cautioned

against prescribing low prescriptions, unless there is recorded evidence of a clinical need.44 Examples of a clinical need are some eye alignment problems or a weakness of the muscles that focus the eyes close to (accommodative insufficiency; discussed in Chapter 3).23 One study that compared a group of dyslexic children with controls found, three times as many dyslexic participants (42%) had been prescribed spectacles compared with the control group (14%).45 However, the proportion of both groups who were using spectacles was similar45 and the distribution of refractive error in the two groups also was similar.17 There are several likely explanations for this finding: parents of dyslexic children are more likely to seek optometric care,3 optometrists may be predisposed to correct low refractive errors

Chapter 2 - Refractive errors & ocular health

33

because they want to try to help children with reading difficulties, and the increased prevalence of symptoms from other conditions such as visual stress and binocular instability may be misinterpreted by practitioners as a need for refractive correction (see Case study 2.2). The scientific evidence justifies a conservative approach to prescribing refractive corrections in these cases: a refractive error that would not normally be corrected should not be corrected just because a child is dyslexic.

Summary Ocular pathology and refractive error do not seem to be commonly associated with dyslexia, but hypermetropia can contribute to reading difficulties. Refractive errors are common in the population, and it is sensible for children with reading difficulties to have an eye examination so that uncorrected refractive errors can be dealt with appropriately. There is no good evidence that a low refractive error is any more likely to require correction in people with reading difficulties than in the general population. In Chapter 10, the clinical protocol for testing people with reading difficulties is discussed in more detail.

References 1. Legge GE, Rubin GS, Pelli DG, et al. Psychophysics of reading--II. Low vision. Vision Res 1985;25(2):253-65. doi: 10.1016/0042-6989(85)90118-x [published Online First: 1985/01/01] 2. Evans BJW, Drasdo N. Review of ophthalmic factors in dyslexia. Ophthal Physiol Opt 1990;10:123-32. 3. Evans BJW. Dyslexia and Vision. Chichester: Wiley 2001. 4. Rima S, Kerbyson G, Jones E, et al. Advantage of detecting visual events in the right hemifield is affected by reading skill. Vision Res 2020;169:41-48. doi: 10.1016/j.visres.2020.03.001 [published Online First: 2020/03/17] 5. Kermani M, Verghese A, Vidyasagar TR. Attentional asymmetry between visual hemifields is related to habitual direction of reading and its

34

Chapter 2 - Refractive errors & ocular health

implications for debate on cause and effects of dyslexia. Dyslexia 2018;24(1):33-43. doi: 10.1002/dys.1574 6. Facoetti A, Turatto M. Asymmetrical visual fields distribution of attention in dyslexic children: a neuropsychological study. Neuroscience Letters 2000;290:216-18. 7. Hari R, Renvall H, Tanskanen T. Left minineglect in dyslexic adults. Brain 2001;124(Pt 7):1373-80. doi: 10.1093/brain/124.7.1373 [published Online First: 2001/06/16] 8. Rutkowski JS, Crewther DP, Crewther SG. Change detection is impaired in children with dyslexia. J Vis 2003;3(1):95-105. doi: 10.1167/3.1.10 [published Online First: 2003/04/08] 9. Polikoff BR, Evans BJW, Legg CR. Is there a visual deficit in dyslexia resulting from a lesion of the right posterior parietal lobe? Ophthal Physiol Opt 1995;15(5):513-17. 10. Pammer K, Wheatley C. Isolating the M(y)-cell response in dyslexia using the spatial frequency doubling illusion. Vision Research 2001;41(16):213947. 11. Edwards JD, DeLeon J, Bearden WH, et al. Is reading disability likely to interfere with glaucoma screening of adults using frequency-doubling technology perimetry? Am J Ophthalmol 2003;135:816-20. 12. Evans BJW, Busby A, Jeanes R, et al. Optometric correlates of Meares-Irlen Syndrome: a matched group study. Ophthal Physiol Opt 1995;15(5):481-87. 13. Scott JC, McWhinnie H, Taylor L, et al. Coloured overlays in schools: orthoptic and optometric findings. Ophthal Physiol Opt 2002;22:156-65. 14. Norn MS, Rindziunski E, Skydsgaard M. Ophthalmologic and orthoptic examination of dyslexia. Acta Ophthalmol 1969;47:147-60. 15. H. A. Opthalmol Status of schoolchildren with dyslexia. Eye 1987;1:61-68. 16. Pinckers A. Color vision and age. Ophthalmologica 1980;181(1):23-30. doi: 10.1159/000309021 [published Online First: 1980/01/01] 17. Evans BJW, Drasdo N, Richards IL. Refractive and sensory visual correlates of dyslexia. Vision Research 1994;34(14):1913-26. 18. Solebo AL. Identification of visual impairments. In: Emond A, ed. Health For All Children. Fifth ed. Oxford: Oxford University Press 2019. 19. Thomson WD, Evans BJW. A new approach to vision screening in schools. Ophthal Physiol Opt 1999;19(3):196-209. 20. Bailey IL, Lovie JE. New design principles for visual acuity letter charts. Am J Optom Physiol Opt 1976;53(11):740-45. 21. Barnard NA. Visual conversion reaction in children. Ophthalmic Physiol Opt 1989;9(4):372-78. 22. Veszeli J, Shepherd AJ. A comparison of the effects of the colour and size of coloured overlays on young children's reading. Vision Res 2019;156:73-83. doi: 10.1016/j.visres.2019.01.006 23. Evans BJW. Pickwell's Binocular Vision Anomalies. Sixth ed. Philadelphia: Elsevier 2021.

References

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24. Dickinson PMA, and Rabbitt CM. Simulated visual impairment - effects on text comprehension and reading speed. Clin Vis Sci 1991;6(4):301-08. 25. Saw SM, Tan SB, Fung D, et al. IQ and the association with myopia in children. Invest Ophthalmol Vis Sci 2004;45(9):2943-48. 26. Stewart-Brown S, Haslum MN, Butler N. Educational attainment of 10-yearold children with treated and untreated visual defects. Dev Med Child Neurol 1985;27(4):504-13. 27. Logan NS, Davies LN, Mallen EA, et al. Ametropia and ocular biometry in a U.K. university student population. Optom Vis Sci 2005;82(4):261-66. 28. Roch-Levecq AC, Brody BL, Thomas RG, et al. Ametropia, preschoolers' cognitive abilities, and effects of spectacle correction. Arch Ophthalmol 2008;126(2):252-58. 29. Kulp MT, Ciner E, Maguire M, et al. Uncorrected hyperopia and preschool early literacy. Ophthalmology 2016;123(4):681-89. doi: 10.1016/j.ophtha.2015.11.023 30. Quaid P, Simpson T. Association between reading speed, cycloplegic refractive error, and oculomotor function in reading disabled children versus controls. Graefes Arch Clin Exp Ophthalmol 2013;251(1):169-87. doi: 10.1007/s00417-012-2135-0 [doi] 31. Rosner J, Gruber J. Differences in the perceptual skills development of young myopes and hyperopes. Am J Optom Vis Sci 1985;62(8):501-04. 32. Rosner J, Rosner J. Some observations of the relationship between the visual perceptual skills development of young hyperopes and age of first lens correction. Clin Exp Optom 1986;69:166-68. 33. Williams WR, Latif AH, Hannington L, et al. Hyperopia and educational attainment in a primary school cohort. Arch Dis Child 2005;90(2):150-53. 34. O'Leary CI, Evans BJW, Edgar DF. The effect of low refractive corrections on rate of reading. Optometry in Practice 2014;15(3):87-100. 35. Yammouni R, Evans BJ. An investigation of low power convex lenses (adds) for eyestrain in the digital age (CLEDA). J Optom 2020;13(3):198-209. doi: 10.1016/j.optom.2019.12.006 [published Online First: 2020/04/27] 36. O'Donoghue L, Rudnicka AR, McClelland JF, et al. Visual acuity measures do not reliably detect childhood refractive error--an epidemiological study. PLoS ONE 2012;7(3):e34441. doi: 10.1371/journal.pone.0034441 [doi];PONE-D-11-13556 [pii] 37. Evans BJW. Case reports: The need for optometric investigation in suspected Meares-Irlen syndrome or visual stress. Ophthal Physiol Opt 2005;25:363-70. 38. Farbrother JE. Spectacle prescribing in childhood: a survey of hospital optometrists. Br J Ophthalmol 2008;92(3):392-95. 39. Cotter SA. Management of childhood hyperopia: a pediatric optometrist's perspective. Optom Vis Sci 2007;84(2):103-09. doi: 10.1097/OPX.0b013e318031b08a [doi];00006324-200702000-00008 [pii] 40. Lyons SA, Jones LA, Walline JJ, et al. A survey of clinical prescribing philosophies for hyperopia. Optom Vis Sci 2004;81(4):233-37.

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41. Shneor E, Evans BJ, Fine Y, et al. A survey of the criteria for prescribing in cases of borderline refractive errors. J Optom 2016;9(1):22-31. doi: 10.1016/j.optom.2015.09.002 42. O'Leary CI, Evans BJW. Criteria for prescribing optometric interventions: literature review and practitioner survey. Ophthal Physiol Opt 2003;23:42939. 43. Jennings A. Behavioural optometry: a critical review. Optometry in Practice 2000;1:67-78. 44. College of Optometrists. F02: Guidance for the issuing of small prescriptions and making small changes to existing prescriptions. www college-optometrists org 2012 5/16/2012. http://www.collegeoptometrists.org/en/professional-standards/Ethics_Guidance/index.cfm. 45. Evans BJW, Drasdo N, Richards IL. Investigation of accommodative and binocular function in dyslexia. Ophthal Physiol Opt 1994;14(1):5-19.

Chapter 3 Binocular vision and accommodative anomalies Chapter abstract The main binocular vision and accommodative anomalies are considered

in

turn:

strabismus,

heterophoria,

convergence

insufficiency, binocular instability, accommodative insufficiency, and accommodative

infacility.

For

each

of

these

conditions,

any

associations with reading difficulties are reviewed, including their cause. The treatment of these conditions is discussed, also addressing the general question of when optometric factors need to be treated. The chapter closes with a summary table. It is concluded that binocular instability (fusional vergence dysfunction) is correlated with dyslexia, but is unlikely to be a major cause of the condition.

Introduction Binocular vision, or binocular co-ordination, describes how the eyes move together and align on objects of regard, controlled by muscles outside the eye. Up to about the age of about 50 years, human eyes can focus on different distances. This ocular accommodation is controlled by muscles within the eye. Together, binocular vision and accommodation are sometimes described as ocular motor functions (confusingly, this has a different meaning to oculomotor, which is variously used in relation to saccadic eye movements or functioning of the third cranial nerve). In this chapter, the main anomalies of binocular vision and © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 A. J. Wilkins and B. J. W. Evans, Vision, Reading Difficulties, and Visual Stress, https://doi.org/10.1007/978-3-031-03930-0_3

37

38

Chapter 3 - Binocular vision and accommodative anomalies

accommodation that could be linked with reading difficulty are discussed. Typically, this link is investigated in research studies that compare two groups of children, one group with reading difficulty (e.g., dyslexia) and the other with normal reading skills (control). Even when research of this type identifies a visual factor that is associated with reading difficulty, this does not necessarily mean that the visual condition is a cause of the reading difficulty. The headings outlined in Chapter 1 are used to determine whether there is an association between a condition and reading difficulty, whether there is a causal relationship, and how the ocular motor anomaly can be detected and treated. When researching binocular vision and accommodation, careful attention needs to be paid to the way the research is undertaken (the research methodology). Some studies have been omitted1 because of methodological difficulties and these are explained in Chapter 12.

Strabismus Background

Chapter 3 - Binocular vision and accommodative anomalies

39

Figure 3.1. Illustration of normal ocular alignment (orthophoria) and various types of misalignment of the eyes, known as strabismus, squint, or heterotropia. Strabismus (squint; heterotropia) occurs when the eyes are misaligned (Figure 3.1). Strabismus can be obvious, as in the figure, or of a very small angle (microtropia) when it will only be detected during an eye examination. Strabismus affects 2-3% of the population.2 Strabismus can be incomitant, when the angle of deviation (misalignment) varies in different positions of gaze; but is more usually concomitant. Strabismus that occurs early in life, whether concomitant or incomitant, does not usually result in double vision because the brain adapts (it has sensory adaptations). This can be conceptualised, in lay terms, as the brain “turning off” (suppressing) the strabismic eye to prevent its (misaligned) image causing double vision. Possibly as a result of this suppression, strabismus in the first few years of life usually results in reduced vision (poorer acuity) in the strabismic eye. This reduced vision in one eye is sometimes called lazy eye, but the preferred term is amblyopia. The amblyopia typically has a negligible

40

Chapter 3 - Binocular vision and accommodative anomalies

effect on performance under normal viewing conditions because the amblyopic eye is suppressed by the brain and the image from the nonamblyopic eye is preferred.3

Is strabismus associated with reading difficulty? Strabismus3 (including microtropia)4 and amblyopia5 6 do not seem to be associated with reading difficulties; nor with eyestrain (asthenopia).7 This applies to both concomitant and incomitant strabismus.

Can strabismus cause reading difficulty? One research study found that the maximum reading speed under binocular conditions (with both eyes) was slower in a group of participants with amblyopia associated with microtropia than in a control group.8 However, it is not clear whether a similar effect was present under normal reading conditions (when people are not trying to read just for maximum speed) and the result may have been influenced by treatment that the amblyopic group was receiving. In general, the authors have found very little evidence suggesting that strabismus is likely to cause reading difficulty and this is probably because of sensory adaptations.2 When strabismus develops in childhood (below the age of 8-13 years), the person usually develops sensory adaptations that prevent the strabismus from interfering significantly with visual perception.2 Rarely, unstable strabismus may interfere with visual perception when reading and these cases usually present with symptoms. The strabismus may be unstable in that the patient rapidly alternates from one eye to the other, or the sensory adaptation may be unstable. In either case, an unstable response would be revealed by sensory tests (e.g., Mallett Foveal Suppression Test, Mallett Large OXO Test, Bagolini

Chapter 3 - Binocular vision and accommodative anomalies

41

lenses).2 Some of these tests are illustrated in Figure 3.2. In these cases, the patient typically reports text blurring, doubling, or moving, and the symptoms are alleviated by closing or covering one eye (or reading with the head at an unusual angle so that the nose occludes one eye). These cases are very rare. It was noted above that strabismus affects 2-3% of the population, and it is only a small proportion of people with strabismus who have the unstable perception described in this paragraph.

Figure 3.2. The Mallett Large OXO Test (top row, left panel),2 Foveal Suppression Test (top row, fourth panel);2 9 and Fixation Disparity Test2 9 for horizontal (bottom left panel) and vertical (bottom right panel) deviations.

Detection of strabismus Most cases of strabismus are detected by a simple test all eye care practitioners use, called the cover-uncover test.2 In a small proportion of cases of strabismus, the angle of deviation may be so small that it is

42

Chapter 3 - Binocular vision and accommodative anomalies

not apparent on cover testing. These cases are usually detected by reduced vision in one eye (amblyopia) and poor performance on tests of stereopsis (stereopsis is a form of depth perception that results from the brain fusing together the images from each eye).

Treatment of strabismus Since strabismus is not likely to contribute to reading difficulty, its treatment will not be considered here. Detailed information on the diagnosis and treatment of strabismus can be found in the textbook Pickwell’s Binocular Vision Anomalies, Sixth Edition (2021).2

Heterophoria and decompensated heterophoria Background Only about 2-3% of people have strabismus. For most people, the eyes are aligned for distance vision and converge appropriately on near objects. However, when one eye is covered the eye behind the cover will often misalign, even when they are usually aligned when both eyes are open. This is called heterophoria and the main types of heterophoria are illustrated in Figure 3.3. There is no consistent evidence of a predisposition towards any type of heterophoria in children with reading problems, including dyslexia.3 10

Chapter 3 - Binocular vision and accommodative anomalies

43

\ Figure 3.3. Illustration of main types of heterophoria, revealed by the position of an eye behind a cover (shown as if transparent). When there is no heterophoria (orthophoria), the eye behind the cover maintains alignment. In horizontal heterophoria, the eye behind the cover turns in (esophoria) or out (exophoria). In vertical heterophoria, the eye behind the cover turns up (hyperphoria), or down (hypophoria; not shown). Another way of describing heterophoria is a dissociated deviation, because the eyes deviate when they are dissociated by covering one eye, or by forcing the eyes to view dissimilar objects. For most people, three factors prevent heterophoria from breaking down into strabismus (Figure 3.4). During everyday vision, we exert motor fusion to align the eyes so that both eyes obtain a similar view and sensory fusion can take place (Figure 3.4). Sensory fusion is possible if each eye obtains similar views, but as the dissimilarity increases the processes of fusion eventually break down, leading to double vision (diplopia). The dissimilarity depends in part on the alignment of the eyes. The power to converge the eyes (turn them inwards) and diverge the eyes (turn them outwards) as necessary to avoid diplopia is referred to as fusion reserves or motor fusion.

44

Chapter 3 - Binocular vision and accommodative anomalies

Size of deviation Sensory fusion

Motor fusion (fusional reserves)

(fusion lock) Compensated phoria or Decompensated phoria or Strabismus

Figure 3.4. A simple model of binocular vision. Phoria, heterophoria. Modified with permission from Evans, B.J.W. (2021) Pickwell’s Binocular Vision Anomalies, 6th edition, Elsevier. Sensory fusion is the process whereby the two monocular percepts are fused into a single image, and this provides information on the relative depth of objects. The role of sensory and motor fusion in helping a person to compensate for heterophoria is summarised schematically in Figure 3.4. If the dissociated deviation is excessive and/or if the sensory and motor fusion are inadequate, then heterophoria may break down to a strabismus. In other cases, although the person does not develop strabismus, because the eyes remained aligned, the person must strain excessively to maintain that alignment. In these cases, there is a decompensated heterophoria. The

most

common

type

of

decompensated

heterophoria

(decompensated exophoria) affects near vision: the two eyes are misaligned because they are insufficiently converged. This can be corrected with spectacles with base in prisms, with concave (minus)

Chapter 3 - Binocular vision and accommodative anomalies

45

lenses, or by eye exercises.2 These methods of correction are discussed in more detail later. Decompensated heterophoria causes symptoms,11 including blur, double vision, visual perceptual distortions (e.g., text appearing to move) and eyestrain and headaches. It is therefore not surprising that it can cause decreased visual performance, in the form of a reduced rate of reading.12

Is decompensated heterophoria associated with reading difficulty? In the UK decompensated heterophoria is typically detected using a test called the Mallett unit, which is described below. This detects a minute tendency for the eyes to misalign, detected as a fixation disparity and measured as an aligning prism (see below).2 Although one early study found fixation disparity to be associated with poor reading,13 subsequent studies found that that the presence of fixation disparity14 15 and magnitude of aligning prism15 are not associated with dyslexia. Although decompensated heterophoria is not a strong correlate of reading problems, it is quite common, may occur in any child and could make reading more difficult.

Can decompensated heterophoria cause reading difficulty? If a person has a refractive error (Chapter 2) or visual stress (Chapter 7) that is causing blur or other visual perceptual distortions, this could interfere with sensory fusion, the left-hand variable in Figure 3.4. In some cases, correction of the refractive error, or possibly of visual stress, may be all that is required to render the heterophoria compensated. This may explain why, exceptionally, patients may be encountered where correction of a low degree of long-sightedness can render an exophoria compensated. Although, because of the link

46

Chapter 3 - Binocular vision and accommodative anomalies

between accommodation and convergence, a long-sighted correction will slightly increase the exophoria,2 sensory fusion may be sufficiently enhanced to compensate. These factors can be investigated clinically using the Mallett Fixation Disparity Test,11 16 17 described in the next section. O’Leary and Evans carried out a randomised controlled trial of patients who were not selected as having any reading difficulty but whose optometric test results indicated decompensated exophoria. The researchers investigated whether base in prisms that corrected the decompensated exophoria improve the reading speed.12 They found, prisms (see below) significantly improve reading speed when the required prism is 2.5' or more. It is interesting to note, the effect of prisms on the Wilkins Rate of Reading Test is modest compared to the effect of coloured filters on this test in people with visual stress (see Chapter 7).

Figure 3.5. The Mallett Fixation Disparity Test, enlarged to show the test for horizontal deviations. The upper green vertical line is seen by one eye and the lower green vertical line by the other eye (as a result of polarising filters). When the two lines are aligned, the eyes are appropriately aligned.

Chapter 3 - Binocular vision and accommodative anomalies

47

Detection of decompensated heterophoria In the UK, a test developed by Mallett in the 1960s has revolutionised

the

detection,

diagnosis,

and

management

of

decompensated heterophoria. This is one of the tests on the Mallett unit (Figure 3.5), the Fixation Disparity Test (enlarged in Figure 3.5). Unlike most binocular vision tests, the Mallett test simulates normal binocular vision because the central text (O X O) and the text surrounding the test are seen by both eyes in the normal way. However, when the patient wears special polarised filters, two features of the test are seen only by one eye: the green Nonius strips. Typically, the green strip above the X is seen by the right eye and the strip below the X by the left eye. A minute misalignment of the strips (fixation disparity) is suggestive of decompensated heterophoria. The strength of a type of lens (prism) that is required to align the strips indicates whether the heterophoria is decompensated and how it might be corrected. Pickwell and colleagues in the 1980s showed, the Mallett fixation disparity test is the best single test for detecting decompensated heterophoria.2 However, no single test is perfect and the diagnosis of decompensated heterophoria is usually based on symptoms and a combination of test results (cover test recovery, aligning prism on the Mallett Unit, and, in the case of exophoria, the adequacy of the fusional reserve that opposes the heterophoria).2 This is discussed further below.

Treatment of decompensated heterophoria There are three main strategies for the management of decompensated heterophoria: eye exercises (vision therapy), refractive

48

Chapter 3 - Binocular vision and accommodative anomalies

correction, or prismatic correction.2 The first two of these are more relevant to children with decompensated exophoria,18 and the most appropriate approach largely depends on the child’s motivation to complete the eye exercises.2 As noted above, prismatic corrections, prescribed based on the results of the Mallett test,19 can significantly improve the speed of reading.12 However, the conventional view was that prisms are not the treatment of choice for young people, since eye exercises or refractive modification may lead to an improvement in underlying function.2 The timescale of the improvement is weeks to months with eye exercises and months to years with refractive modification. Therefore, many eyecare practitioners took the view that eye exercises would be a better approach, if the child and parents are willing. This conventional view has been thrown into question by a large and thorough multi-centre research study, CITT-ART.20

21

This study

investigated 310 children aged 9-14 years with a particular type of decompensated heterophoria: exophoria associated with convergence insufficiency (described below). The eye exercises were very thorough, involving exercises at home and in the clinic for 16 weeks. Importantly, there was a control group who received sham exercises, carefully designed to give them the same time and attention as the children receiving the “genuine” treatment. Two key clinical tests showed greater improvement in the group receiving the real treatment than the control, so eye exercises do seem to change visual function in this condition. Symptoms improved, but the magnitude of improvement did not differ significantly in the two groups and nor did the reading performance, which was assessed thoroughly. In other words, vision therapy was no better than a placebo at improving symptoms and reading performance.

Chapter 3 - Binocular vision and accommodative anomalies

49

The CITT-ART study, published in 2019, has important implications. Although the authors only studied one condition and one system of eye exercises, the condition they studied (decompensated near exophoria) is the one for which eye exercises are most commonly prescribed. Some other conditions, such as esophoria, are generally thought to respond less well to eye exercises. If there is a concern that a case of decompensated exophoria may worsen to a strabismus, eye exercises are likely to be worthwhile because the CITT-ART trial found an improvement in test results that indicate better control of the exophoria. However, if it is thought that an exophoria is contributing to symptoms, the CITT-ART results indicate that eye exercises are not likely to be the best approach. This conclusion applies to the condition studied in the CITT-ART trial, near decompensated exophoria associated with convergence insufficiency. The results may not apply to a simpler condition, when there is a convergence insufficiency that exists in isolation without a decompensated exophoria. This is discussed next. The CITT-ART study excluded children with phonologically based reading difficulties. Therefore, it is not known whether the results also apply generally to people with dyslexia. There is some evidence that cognitive load influences binocular co-ordination.22 It is therefore possible that the extra cognitive load required by dyslexics when reading could make them more prone to binocular vision anomalies. However, this is speculation.

Convergence insufficiency Background Convergence describes the turning in of the eyes to maintain alignment on a target that approaches the nose. Convergence insufficiency, in its simplest form, is characterised by a remote near

50

Chapter 3 - Binocular vision and accommodative anomalies

point of convergence (the nearest point to which the eyes can converge). The term is also sometimes used to describe a decompensated exophora for near vision when associated with a convergence

insufficiency

(convergence

insufficiency

exophoria

syndrome or CIES).2 In this book, when the term convergence insufficiency is used alone it solely refers to a remote near point of convergence.

Is convergence insufficiency associated with reading difficulty? A review in 2001 noted controversy as to whether convergence insufficiency is a correlate of dyslexia.3 Only one study since 2001 has found a slightly more remote near point of convergence in a group of children with dyslexia than in a control group.23 Other studies have found no significant difference in the near point of convergence of a group of dyslexic children compared with controls. 10

24

Of course,

dyslexia may have many causes, and if convergence insufficiency is in fact a cause, but only one among many, it is unlikely to be detected in a group of dyslexic individuals unless the study is very large. Convergence insufficiency does appear to be associated with attention deficit hyperactivity disorder (ADHD),25 although this could be an artefact owing to poor concentration on the task. In any event, convergence insufficiency is such a prevalent condition that it will be encountered quite commonly in both good and poor readers.

Can convergence insufficiency cause reading difficulty? In view of the weak correlation between convergence insufficiency and reading difficulty it is unlikely that there is a major causal relationship. However, there is evidence that in some individuals with dyslexia,

convergence

insufficiency

may

be

associated

with

symptoms,26 which could contribute to the burden a dyslexic child experiences when reading.

Chapter 3 - Binocular vision and accommodative anomalies

51

Figure 3.6. RAF rule used to measure near point of convergence or accommodative amplitude.

Detection of convergence insufficiency Convergence insufficiency is easily detected as a remote near point of convergence.27 This can be measured with a handheld target and ruler, or with an instrument that has a target on a slide that moves along a ruler. An example of this type of test is the RAF rule (Figure 3.6).

Treatment of convergence insufficiency Eye exercises are the usual approach for treating convergence insufficiency.2 The CITT-ART study investigated a more complex condition,

convergence

insufficiency

associated

with

near

decompensated exophoria (CIES)2. In that study, symptoms improved no more with a thorough system of eye exercises than with placebo

52

Chapter 3 - Binocular vision and accommodative anomalies

eye exercises, but there was a significant improvement in the near point of convergence. It seems likely that the symptoms were attributable, in large part, to the decompensated exophoria that would affect people at their normal reading distance. Therefore, in patients with the simpler problem when the anomaly is a remote near point of convergence, it seems reasonable to expect that eye exercises will be effective at improving the near point of convergence. The IFS programme of exercises (Figure 3.7) was developed by one of the authors at the Institute of Optometry to treat convergence insufficiency. An initial open trial found this system of exercises improved the near point of convergence and symptoms.28 A recent randomised controlled trial found that IFS exercises improve near point of convergence and convergent fusional reserves, but not symptoms.29 The authors of this trial cautioned, this finding may be because the symptoms were reassessed too soon after the eye exercises stopped. Nonetheless, this finding is similar to the CITT-ART findings described above and adds to the evidence that eye exercises (vision therapy) should not be advocated as a widespread approach to treating symptoms and are not likely to improve reading performance. In cases where the near point of convergence is receding, it may be helpful to improve the near point of convergence with exercises before it reaches the stage where symptoms are likely.2 IFS exercises are designed to be carried out by the patient, usually a child, at home; but they are more comprehensive and intensive than home exercises typically used in the UK. There are a series of four target cards which the patient views and which create a variety of stereoscopic perceptions. The exercises come with detailed documentation which gives the parent (or the patient if an adult) a programme of instructions to take them through a series of tasks, each gradually building their

Chapter 3 - Binocular vision and accommodative anomalies

53

convergent fusional reserves and other relevant functions. There are also instructions for the practitioner, who typically sees the patient for a first follow-up about three weeks after the exercises are dispensed. The IFS exercises, like other orthoptic exercises, should only be prescribed by eye care professionals who can select appropriate patients and monitor progress.

Figure 3.7. Institute Free-Space Stereogram (IFS) exercises. Sheard’s criterion (an assessment of the adequacy of the fusional reserves that are used to overcome the heterophoria) has been shown to be useful in the diagnosis of decompensated exophoria;30

31

but

does not seem to be a useful method of prescribing prisms.32 Dusek and colleagues evaluated children who had reading difficulties that were not attributed to a learning difficulty but due

54

Chapter 3 - Binocular vision and accommodative anomalies

instead to a convergence insufficiency.33 Some children opted for eye exercises and others for spectacles with prisms and both these interventions were found to be helpful for reading compared with a group who opted for no treatment. However, the authors point out that this was not a randomised controlled trial33 and the lack of any intervention for the control group means that placebo effects could account for the results.

Binocular instability (fusional vergence dysfunction) Background Binocular instability is a condition characterised by low fusional reserves and an unstable heterophoria.34

35

In North America, the

condition is called fusional vergence dysfunction. Binocular instability is not the same as decompensated heterophoria, although sometimes the conditions overlap and are both present in the same individual (Table 3.1). An unstable heterophoria can be detected with tests of heterophoriaHowever, it is most likely to be clinically significant if it is present under more natural conditions, using the Mallett Fixation Disparity Test (Figure 3.5). With the Mallett test, it is important to ask patients whether there is any movement of one or both Nonius bars; such a finding is often associated with symptoms.11

Chapter 3 - Binocular vision and accommodative anomalies

55

Table 3.1. Differential diagnosis of binocular instability & decompensated heterophoria (reproduced with permission from Pickwell’s Binocular Vision Anomalies, 6th edition, Bruce Evans, Elsevier, 2021).2 Sign

Binocular instability

Decompensated heterophoria

Heterophoria

May be present, or may be orthophoric (no strabismus or heterophoria)

Heterophoria must be present

Stability of heterophoria2

Unstable: movement of arrow in Maddox wing test usually r 2' or more

Stable or unstable: movement of arrow in Maddox wing test usually less than r 2'

Cover test2

Recovery may or may not be normal

Recovery usually slow and hesitant

Fusional reserves

Usually both convergent and divergent reserves are low, so fusional amplitude ±2'). These diagnostic signs are combined in the scoring system in Table 3.2.

Chapter 3 - Binocular vision and accommodative anomalies

59

Figure 3.8. Prism bar used to measure fusional reserves (see Chapter 10). Joss and Jainta found that some clinical tests of binocular coordination only demonstrated a weak to moderate correlation with dynamic measures of vergence alignment when eye movements were recorded during reading.58 However, the 65 participants were all nondyslexic with normal visual function and fairly low symptom scores, and the Mallett test was not included.

Treatment of binocular instability The management of binocular instability is first to remove any obstacle to sensory fusion. For example, any significant refractive errors should be corrected. If binocular instability persists, if a direction for the deviation in binocular instability is apparent (e.g., exophoria), the management of the condition is the same as the management of decompensated heterophoria described above. If there is no significant heterophoria then the next stage is to improve the motor fusion (Figure 3.4) with fusional reserve exercises. In binocular instability, the underlying problem is low fusional reserves and it has been shown in well-controlled studies that fusional reserves improve with a programme of eye exercises.20 21 29 It seems likely that any symptoms directly attributable to the low fusional reserves would

60

Chapter 3 - Binocular vision and accommodative anomalies

improve when the fusional reserves improve. However, the effect of eye exercises on symptoms in binocular instability has not been investigated in large randomised controlled trials, so the effectiveness of this treatment awaits validation.

Accommodative anomalies Background Ocular accommodation is the ability to change the focus of the eye between its relaxed state, when looking in the distance, and its accommodated state, focussed for near vision. There are three main clinical methods of assessing accommodation: 1. Accommodative amplitude is the maximum accommodation that can be exerted, measured as the nearest point to which the person can accommodate.27 It is often measured with the RAF rule (Figure 3.6), the limitations of which recently have been highlighted.59 60 2. Accommodative lag is the extent to which the person’s actual accommodation lags that required for the target. Usually, it is measured by objective methods, requiring no patient response other than viewing a target.2 3. Accommodative facility is the rate at which the accommodation can be changed.2

As

noted

hypermetropia

in

Chapter can

2,

attempt

young to

people

compensate

with for

uncorrected this

with

accommodation, which would cause an abnormal response on tests of accommodation. Therefore, accommodative anomalies can only be

Chapter 3 - Binocular vision and accommodative anomalies

61

diagnosed with certainty once latent hypermetropia has been ruled out, typically requiring drops that relax the accommodative muscles (cycloplegic refraction).2

Are accommodative anomalies associated with reading difficulty? Evans and colleagues found that a group of children with dyslexia had a slightly lower median amplitude of accommodation (16D) than a group of control children without dyslexia (20D).15 More recent research also finds marginally lower amplitude of accommodation in dyslexia than in controls.10 24 Two studies of children with non-dyslexic reading difficulties find lower amplitudes of accommodation and accommodative facility than controls, but neither study controlled for potentially confounding variables such as intelligence and attention deficit disorder.41 Pattern glare is discussed in Chapter 8 as several lines of evidence point to its role in visual stress, the condition that appears to be helped by

coloured

filters.

Research

that

measured

accommodation

objectively indicates that symptoms of pattern glare are not strongly associated with accommodation.61

Can accommodative anomalies cause reading difficulty? One of the studies that found slightly reduced amplitude of accommodation in dyslexia15 found no difference between the groups in accommodative lag whilst the marginally reduced median accommodation amplitude was not found to significantly impair performance at a visual search task. In the other studies cited above where reduced amplitude of accommodation was found to be associated with dyslexia, the difference in mean binocular amplitude in the two groups was only 1-2D. In general, such a small difference is

62

Chapter 3 - Binocular vision and accommodative anomalies

unlikely to be clinically significant.10

24

However, this finding might

indicate that children with reading problems are slightly more likely to suffer from accommodative insufficiency compared to good readers, and there is some evidence that accommodative insufficiency in dyslexia can cause symptoms when reading.26 Therefore, it is sensible for children with reading difficulties to have a careful assessment of their accommodative function. Two studies, one of accommodative facility62 and one of combined accommodative and vergence facility, 15 have failed to find a relationship between infacility and dyslexia. In summary, children with dyslexia are a little more likely to have accommodative insufficiency. This is unlikely to be a major cause of dyslexia, but could cause symptoms when trying to read, in which case treatment is likely to be of some help.

Detection of accommodative anomalies The clinical protocol for testing accommodation is described in more detail in Chapter 10. The most common test is the push up test, which measures the amplitude of accommodation (Figure 3.6).27 59 60 A method of measuring accommodative lag is the monocular estimation method (MEM), when the clinician uses light reflected from the back of the eye to measure the lag. This has the advantage of not requiring a subjective response. Accommodative facility is especially relevant if a child has problems copying from the board (i.e., changing focus from distance to near and vice versa) although this symptom also can result from non-optometric problems, such as poor short-term memory. One study argued that accommodative insufficiency is the primary source of symptoms in children diagnosed with convergence insufficiency,63 although this has been disputed.64

Chapter 3 - Binocular vision and accommodative anomalies

63

Treatment of accommodative anomalies Accommodative anomalies can be treated with spectacles or eye exercises.65 The prescription for spectacles can be determined with usual clinical methods.2 A variety of approaches are available for accommodative exercises, and it seems most sensible to concentrate on the area(s) of accommodative function where the child has most difficulty.2

When is optometric treatment necessary? The views expressed in this chapter might result in about 5-15% of children with reading problems receiving optometric intervention, such as spectacles or eye exercises. Some optometric philosophies argue that a much higher proportion of children with reading problems should be treated, reflecting a wide variety of views concerning which cases require treatment. One argument is ‘If there is even a faint possibility that optometric treatment will help, then why not have a go?’ But there are some difficulties with this approach, that will now be discussed. Optometrists have a duty to treat patients who need treatment, but also to only treat those cases that are likely to benefit from intervention. Parents of children with reading problems are often desperate to do anything they can to help their children, but financial resources and time will inevitably be limited. Time is especially relevant, because these children will often require extra teaching and homework. Specialist teaching is well known to help with reading problems, and this can be especially effective if it is systematic and in small groups or on a one-to-one basis.66 People with reading or other academic problems should be referred to eye care practitioners who have specialised in vision and learning

64

Chapter 3 - Binocular vision and accommodative anomalies

and who will carry out an in-depth assessment of visual function (see Chapter 10). This in-depth assessment, sometimes called a ‘special investigation’, will require about a dozen different tests of binocular and accommodative function. The probability of having a problem detected increases with the number of tests undertaken. So, if practitioners prescribe spectacles or eye exercises to every patient who fails one test from a large battery of tests, they will treat a high proportion of cases, probably including many who do not need treatment. In other words, a normal patient is just a patient who has not been tested enough! The solution to this problem is to combine test results and this approach has been used in the algorithm in Table 3.2 for the diagnosis of decompensated heterophoria and binocular instability. No approach or algorithm is perfect and experienced clinicians will make a careful decision about whether to treat based on the complete clinical picture, and on the results of repeated measurements over time.

Chapter 3 - Binocular vision and accommodative anomalies

65

Table 3.2. Algorithm for diagnosing decompensated heterophoria† and binocular instability. Reproduced with permission from Evans, B.J.W. (2021) Pickwell’s Binocular Vision Anomalies, 6th edition, Elsevier. DISTANCE / NEAR

score

(delete)

1. Does the patient have one or more of the symptoms of decompensated heterophoria (headache, aching eyes, diplopia, blurred vision, distortions, reduced stereopsis, monocular comfort, sore eyes, general irritation)?

If so, score +3 (+2 or +1 if borderline) Are the symptoms at D or N All the following questions apply to D or N, as ticked (if both ticked, complete 2 worksheets) 2. Is the patient orthophoric on cover testing? Yes or No 3. Is the cover test recovery rapid and smooth? Yes or No

If no, score +1 If no, score +2 (+1 if borderline)

4. Is the Mallett horizontal aligning prism: Display & Text Size>Colour Filters>Colour Tint. They can then vary the hue and “intensity” (roughly saturation) separately, using sliders, without changing brightness (Figure 9.8). Similar settings are available for Android, although they differ between phone manufacturers.

Figure 9.8. Options in the Colour Filters setting of AppleTM iOSTM for iPadTM and iPhoneTM.

248

Chapter 9 - Coloured filters: clinical tools

These electronic adaptations are favoured by some children who would rather avoid coloured filters for cosmetic reasons. The main limitation of the adaptations is that they can only be used on the device for which they were developed and would not, for example, assist the child when reading a book, or using a different digital device. Reading speed depends partly upon the similarity in size and spacing between one letter stroke and another. In some fonts the word minimum consists of regular strokes. Compare

minimum printed in

Times with minimum printed in Open Sans and you can see that Times has regularly spaced letter strokes whereas Open Sans does not. The regularity reduces reading speed: it takes longer for the eyes to re-align after each rapid eye movement (saccade) because the alignment then has to be more precise, presumably the images of the stripes in the two eyes can be mismatched.12 With electronic text the user has the option to choose more readable fonts, and Google Open Sans is a good example.13 There is also the option to increase line spacing. Generally speaking it is important to decrease the ratio of x-height to line spacing as much as practical.13 (x-height is the height of the central body of letters, ignoring ascenders and descenders). This can mean that small fonts are acceptable provided the line spacing is sufficient.

Coloured lighting It is now possible to purchase LED lamps which can be controlled over WiFi so as to provide light with any colour within a large gamut of colours. These may provide an alternative to tinted spectacles in individuals with autism who may find spectacles uncomfortable to wear. However, it is important to ensure that the electronic circuitry

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controlling the LEDs does not result in flicker, and that the gamut of the lamps is sufficiently large and easily controlled.

Other approaches to reducing symptoms from visual stress For some people, coloured filters almost completely eliminate the symptoms of visual stress but for others they are only partially helpful. Other strategies that can be used to reduce the symptoms of visual stress include the following: • increasing the font size and line spacing so as to maintain or decrease the ratio of x-height/line spacing; • avoiding high contrasts by printing work on grey or recycled paper and using a grey background on white boards; • where possible, adjusting light levels; • some people with visual stress experience symptoms from flicker. These people will find it helpful to avoid fluorescent lights with magnetic control circuitry and LED lighting that is poorly stabilized. • many modern LED computer screens also flicker as this is an inexpensive way for manufacturers to dim the screen. However, for some people with visual stress this can cause discomfort. An internet search for “PWM computer monitors” is likely to reveal upto-date information on flicker rates with different computer screens.

Other tools used in the assessment of visual stress The Wilkins Rate of Reading test is commonly used in the assessment of visual stress and was described in Chapter 6. The role

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of this test in the assessment of people with suspected visual stress is described in Chapter 10. The Pattern Glare Test is a particularly useful tool in the assessment of visual stress because it does not require any assessment of colour preference. This test is described in Chapter 10.

Summary Contemporary use of coloured filters for treating visual stress has its basis in the research and protocols reviewed here. The method of use of coloured filters is described in greater detail in the various test instructions and instrument manuals and is integrated with other clinical tests involved in the examination of people with reading difficulties in Chapter 10.

References

251

References 1. 2.

3.

4. 5. 6.

7.

8. 9.

10.

11. 12. 13.

Wilkins AJ, Aldrich A, Lovell-patel R, Allen P, Wilkins A. The repeatability of colorimetry is precise(ly) as expected. 2018;3:1–6. Evans BJW, Allen PM, Wilkins AJ. A Delphi study to develop practical diagnostic guidelines for visual stress (pattern-related visual stress). J Optom. 2017;10. Wilkins AJ, Sihra N, Myers A. Increasing reading speed by using colours: Issues concerning reliability and specificity, and their theoretical and practical implications. Perception. 2005;34. Wilkins A, Sihra N, Smith IN. How precise do precision tints have to be and how many are necessary? Ophthalmic Physiol Opt. 2005;25:269–76. Waldie M, Wilkins A. How big does a coloured overlay have to be? Ophthalmic Physiol Opt. 2004;24:57–60. Smith L, Wilkins A. How many colours are necessary to increase the reading speed of children with visual stress? A comparison of two systems. J Res Read. 2007;30. Lightstone A, Lightstone T, Wilkins A. Both coloured overlays and coloured lenses can improve reading fluency, but their optimal chromaticities differ. Ophthalmic Physiol Opt. 1999;19. Wilkins AJ, Patel R, Adjamian P, Evans BJW. Tinted spectacles and visually sensitive migraine. Cephalalgia. 2002;22:711–9. Evans BJW, Patel R, Wilkins AJ, Lightstone A, Eperjesi F, Speedwell L, et al. A review of the management of 323 consecutive patients seen in a specific learning difficulties clinic. Ophthalmic Physiol Opt. 1999;19. Evans BJW, Stevenson SJ. The Pattern Glare Test: A review and determination of normative values. Ophthalmic Physiol Opt. 2008;28:295– 309. Maclachlan A, Yale S, Wilkins A. Open trial of subjective precision tinting: a followǦup of 55 patients. Ophthalmic Physiol Opt. 1993;13. Jainta S, Jaschinski W, Wilkins AJ. Periodic letter strokes within a word affect fixation disparity during reading. J Vis. 2010;10:2. Wilkins A, Smith K, Penacchio O. The influence of typography on algorithms that predict the speed and comfort of reading. Vis. 2020;4.

Chapter 10 Clinical protocol Chapter abstract This chapter starts with an introduction outlining the evidencebased approach, and a flow-chart summarising the typical procedure for investigating visual factors that may be relevant to reading difficulties. The limitations of a diagnosis of exclusion, as applied to visual stress, is discussed. Symptoms are considered in detail, noting that many symptoms can be caused by a variety of conditions. The main components of the eye examination are summarised, together with the diagnosis of binocular and accommodative anomalies and of visual stress. The key diagnostic tests and criteria for visual stress are described. This chapter is largely aimed at eye care practitioners but may also be of interest to education professionals and parents who are interested in the investigations that eye care practitioners are likely to undertake. The last two sections of the chapter, which relate to funding and finding an appropriate practitioner, are also likely to be of interest to non-eye care practitioners.

Introduction The role of the eye care practitioner is to detect and treat any visual problems that may be contributing to reading difficulties,1 or causing additional barriers that might deter a child from accessing education. A person does not need to have been diagnosed as having a condition such as dyslexia before seeking help from an eye care practitioner. Indeed, it would seem sensible for any children whose teachers or parents suspect underachievement at school to have a detailed © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 A. J. Wilkins and B. J. W. Evans, Vision, Reading Difficulties, and Visual Stress, https://doi.org/10.1007/978-3-031-03930-0_10

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investigation with a practitioner who has specialised in vision and learning. Optometrists and opticians have a statutory duty to assist patients in making informed decisions about their care and to respect the choices they make.2 Optometry, in common with other healthcare professions, has many interventions for which the evidence base is not strong.3 The evidence-based model of healthcare has clear guidance for this commonplace scenario, where strong evidence is lacking. Sackett and colleagues define evidence-based practice as ‘integrating individual clinical expertise and the best external evidence’, with a consideration of patient preferences considered as part of good clinical expertise.4 Satterfield and colleagues modified Sackett et al.’s early model by putting clinical expertise in the middle of the three considerations of evidence-based practice, as this skill allows the integration of all three (Figure 1).5

Figure 10.1. Satterfield’s remodelling of the initial three-circle model of

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evidence-based practice. (Reproduced with permission from Satterfield et al., 2009, The Millbank Quarterly, Wiley).5 It is clear from Figure 10.1, in the evidence-based model, research evidence does not replace, but rather complements, both the clinician’s clinical expertise and patient preferences. Eye care practitioners also have a duty to assist patients in making informed decisions about their care, so controversial topics should be acknowledged as such. This chapter is aimed at the busy eye care practitioner who wants to know how they can integrate the information in this book into a clinical protocol for their patients with reading difficulties. Figure 10.1 gives an overview of this protocol used to investigate children presenting with reading difficulties.6 7

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Figure 10.2. A clinical protocol for the investigation and management of children with reading difficulties and/or symptoms with text, as might be undertaken by a community optometrist or in the hospital eye service. VS, visual stress. *Alternatives to colorimetry and precision tints are, for people who predominantly work on one digital device, changing the screen background colour (Chapter 9). For children, the tint colour is usually checked annually. For adults, the tint colour is usually stable and annual checks typically are not required (Chapter 9).

The notion that conventional visual problems should be excluded before coloured filters are tried is not new and was originally stressed by Irlen.8 In 1991, Evans and Drasdo went further and argued that a particularly thorough eye examination is required to rule out conventional visual problems, and they argued that this “special investigation” should concentrate on the optometric correlates of dyslexia.9 These correlates are detailed in Chapters 2-4. In the UK, the College of Optometrists guidance recommends that when

examining

patients

with

specific

learning

difficulties,

optometrists “should explore visual problems by means of a thorough eye examination”.10 As always, it is recommended that clinicians keep adequate clinical records. Lightstone and Evans outlined the clinical routine for a special investigation,6 7 and this is discussed further in Chapters 2-4 and below. The usual recommendation is for visual stress only to be diagnosed if other potential optometric correlates of dyslexia have been excluded. This means that visual stress is a “diagnosis of exclusion”. There are some difficulties with this diagnosis of exclusion, and these difficulties will now be summarised.

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Limitations of a diagnosis of exclusion The conventional problems that should be excluded before coloured filters are prescribed are summarised in Figure 10.2 in three categories: ocular health, refractive error, and orthoptic anomalies. For each of these categories, there is a variety of opinions on the range of tests that are appropriate and when treatment is necessary. There are many prescribing philosophies concerning refractive error 11 12 and an even greater diversity of opinions as to when orthoptic problems exist and should be treated.13 14 Practitioners often react to uncertainty about the diagnosis of orthoptic conditions by applying a battery of tests. Clearly, thoroughness is commendable, but it needs to be borne in mind that when more tests are carried out there is a greater chance of a patient failing at least one of these tests. In other words, ‘a normal patient is just one who has not been tested enough’! A scoring system is suggested in the algorithm in Chapter 3 (Table 3.2) which addresses this issue,14 and which has been used in several research studies.15-17 Another difficulty is that the conditions in Figure 10.2 to be excluded before a diagnosis of visual stress is reached gives the diagnostic process a hierarchical nature which, in some cases, might be inappropriate. Clearly, if a person has a serious ocular disease or a large uncorrected refractive error, the priority should be to manage these conditions. But low degrees of long-sightedness or astigmatism are commonplace and might only be considered to require correction if the person reports an appropriate symptom, such as blurring.11 12 18 19

If the blurring results from visual stress, this means patients have to

go through a stage in which glasses are prescribed unnecessarily before the appropriate intervention in prescribed. Similarly, if a patient has eyestrain or double vision resulting from visual stress but also happens to have a subtle binocular vision

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anomaly, then they might have to go through a time-consuming course of eye exercises before they are allowed to have coloured filters. The CITT-ART trial is, to date, the most thorough randomised controlled of eye exercises (vision therapy) for a binocular vision anomaly. 20 21 This study showed that prolonged thorough exercises were no more effective than a placebo at improving symptoms20 or reading.21 Nearly 40% of the group receiving vision therapy still had significant symptoms or minimal improvement in symptoms after treatment. 20 Some clinicians have questioned the hierarchical nature of Figure 10.2, arguing that subtle orthoptic anomalies may only be diagnosed safely once visual stress has been excluded. The reasoning is that if visual stress is causing a patient to have an unstable perception of text, this will make it harder for the visual system to control the eye alignment. In some cases, orthoptic function improves once the visual stress has been treated. So, insisting on perfect orthoptic function before prescribing Precision Tinted Lenses may be ‘the cart leading the horse’. This may explain why some orthoptic (ocular motor) conditions are correlated with visual stress.22-24 One approach, suitable for adults and older children whose responses are reliable, is to investigate the effect of possible interventions on symptoms. For example, if a patient reports text moving, blurring, and flickering and they have a low refractive error and signs of visual stress, the practitioner could compare, whilst the patient views text, the effect of a refractive correction with the effect of the optimal coloured filter. The patient is asked what effect, if any, either and both interventions have on their symptoms.

Symptoms to look for There are many symptoms that can lead a practitioner to suspect their patient may be susceptible to one of the two main correlates of

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SpLD (visual stress and binocular instability). Some of the most common symptoms include those listed in Table 10.1. Examples of some symptoms than can be useful in assessing people with SpLD. N.B., this list is not exhaustive. ADHD, attention deficit/hyperactivity disorder., but this is not an exhaustive list. It would be helpful if practitioners could predict what type of visual problem a person has from their symptoms. Unfortunately, most of the visual symptoms that are common in reading difficulties can have several causes.25 Nonetheless, some symptoms do suggest the possibility of the conditions indicated in Table 10.1.

Table 10.1. Examples of some symptoms than can be useful in assessing people with SpLD. N.B., this list is not exhaustive. ADHD, attention deficit/hyperactivity disorder. Symptom or history

Comment

Is the SpLD mainly with reading, spelling, writing, or mathematics?

Sometimes reading may be adequate, but nonetheless capable of improvement.

Is there a history of spectacle wear?

Evans and colleagues6 found, children with SpLD are more likely to have been prescribed spectacles, but often are not using them. This may indicate an enthusiasm for practitioners to try borderline refractive errors, even though there is no evidence they are more likely to help children with SpLD compared with good readers (Chapter 2).

Is there a history of eye exercises or patching?

Children may have received eye exercises or vision therapy as treatment for binocular vision anomalies, or for other reasons (Chapter 4). Patching might indicate amblyopia.

Is there a history of

The required colour may change. So, discontinued

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coloured filter use?

use of coloured filters in the past does not necessarily mean that filters are no longer required.

Is there a history of epilepsy, “fits, faints or funny turns”?

Some people with photosensitive epilepsy can be helped by using coloured filters (Chapter 11).26

Are there headaches (if so, frequency, type, severity, location, associated factors, triggers)?

Headaches when reading or from lights or patterns can be a sign of visual stress, particularly if the headaches have the characteristics of migraine. Migraine is sometimes alleviated by using precision tinted lenses.27 Headaches can also be triggered by binocular vision anomalies15 28 or uncorrected refractive errors,29 30 although most headaches are non-ocular in origin.31

Is reading usually Blurring can be a sign of refractive errors, clear; does it ever go accommodative defects, orthoptic anomalies, dry blurred? eye, or visual stress. For some children, text is initially clear and then blurs. Some children answer questions literally. Therefore, questioning needs to ask not just whether text is clear, but also whether text blurs. Do letters or words stay still, or do they move?

Moving text is a common symptom of visual stress but can also be a sign of binocular vision anomalies.14 Again, the movement may only happen after reading for a while, so the questioning should reflect this.

Do letters or words change size or fade or disappear?

These symptoms can indicate anomalies of binocular co-ordination or accommodation, latent hypermetropia; or visual stress.

Do you have trouble changing your focus from viewing the board to a book?

This could be a sign of accommodative dysfunction or poor binocular co-ordination. Alternatively, there may be no visual cause since people with dyslexia often have poor short-term memory and copying from the board requires the person to hold information in short-term memory.

Do you ever experience double

Double vision is a classic sign of a binocular vision anomaly but can also be a sign of visual stress.

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vision?

Double vision can be demonstrated (e.g., with an insuperable vertical prism) so that the child knows what the term means. If double vision is eliminated by cover one eye, it probably results from a binocular vision anomaly.

Do you ever experience sore or tired eyes (e.g., when reading)?

Can be a sign of refractive, binocular, accommodative and anterior segment anomalies (e.g., dry eye), visual stress, or just tiredness. If linked specifically with reading (e.g., ‘Reading hurts my eyes and I have to stop’) rather than, for example drawing, suggestive of long-sightedness, near point binocular vision anomalies, or visual stress.

Do you hold reading May be a sign of refractive, binocular, or unusually close or accommodative anomalies, visual stress, or just a far away? habit. Do you ever close or This symptom is strongly suggestive of a binocular cover one eye? anomaly. Occasionally, can be a sign of visual stress (closing one eye halves the input to the visual cortex) Do you tend to skip or omit words or lines?

Can be a sign of visual stress, ADHD, a binocular anomaly, or just late reading development (“top down”). Rarely, it might be a sign of an eye movement anomaly.

Does the page seem Can be a sign of visual stress (e.g., ‘the page is so too bright? bright that it stops me seeing the words properly’). Are you particularly sensitive to light?

Can be a sign of visual stress, a binocular vision anomaly, or other ocular conditions. Photophobia and frequent headaches seems to be a strong indicator that precision tinted lenses may help.32 However, a sudden increase in photophobia can be sign of various ocular pathologies (e.g., uveitis, angle closure glaucoma, corneal ulcer) or systemic pathology.

Is there a family history of learning problems?

SpLD tends to run in families.

Is there a family

Orthoptic problems tend to run in families.

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history of orthoptic problems? Is there a family history of migraine?

Migraine headaches tend to run in families and can sometimes be helped with precision tinted lenses.

Is there a family history of visual stress?

Visual stress seems to run in families,33 34 although more research is required.

The term visual perceptual distortion is sometimes used to describe generically several symptoms that can occur when viewing text (e.g., blurring, doubling, movement, patterns, fading, colours). Children may fail to describe any symptoms for a visual condition that would, in an adult, cause complaints. Yet, once the condition has been corrected the child may then comment on the initial symptom that has now been alleviated. If the symptom has been perceived for a long time, the child may be so habituated to this that it appears to them “normal”. This needs to be stressed to teachers: it is not safe for them to conclude that if a child does not report visual symptoms, they do not need an eye examination. Even when children do describe visual symptoms, their reports are often difficult to interpret. Whilst many adults can clearly differentiate between blurring, doubling, and words moving; children may not. Even if they can, these symptoms are nonspecific. In other words, several different visual problems can cause similar symptoms (see Table 10.1). Many of the visual symptoms in Table 10.1 do not occur immediately, but rather after the child has been reading for a while. As indicated in the table, questioning of the patient needs to detect this. For example, some children who would say “no” to the question “Are words in a book normally blurred?” would say “yes” if asked “Do words in a book ever go blurred?”

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Although the absence of symptoms does not imply that an eye examination is unnecessary, the presence of visual symptoms does indicate the need for an eye examination. Nonetheless, the presence of symptoms does not necessarily mean that a visual problem is present. Just asking about a symptom will be enough to convince some children that they suffer the symptom, even when they don’t! It is recommended in this book that eye care practitioners specialising in this field should carry out a detailed investigation of visual function in people with reading difficulties. It is useful to send out a questionnaire in advance of these appointments and this might include, as a starting point, the questions listed in Table 10.1. A link to such a questionnaire that can be downloaded and modified by practitioners for their own use is included in the Appendices.

The eye examination This book has discussed several visual problems that can be associated with reading difficulties. These conditions can cause similar symptoms, so the eye care practitioner is faced with a challenge of differential diagnosis, requiring a comprehensive eye examination.14 The eye examination would typically include the components listed in Table 10.2.

Table 10.2. Components of the eye examination for people with SpLD. Not all tests may be appropriate in every case. General description

Details

Refractive error & visual acuity

Presenting vision at distance & near Retinoscopy Subjective refraction Corrected visual acuity

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Health assessment

Pupil reactions Ophthalmoscopy Visual fields (if old enough) Colour vision (Ishihara)

Ocular motor assessment

Cover-uncover test at distance and near Dissociation test at distance & near (e.g., alternating cover test, Maddox rod, Maddox wing) Aligning prism at distance & near (Mallett fixation disparity test) Ocular motility Near point of convergence Fusional reserves at near (possibly distance) Vergence facility Stereoacuity Amplitude of accommodation Accommodative retinoscopy)

lag

(MEM

Facility of accommodation Coloured filter screening

Intuitive Overlays Wilkins Rate of Reading Test Pattern Glare Test

Coloured filter prescribing

Intuitive Colorimeter Precision tinted lenses

Most of the tests in Table 10.2 will be familiar to optometrists, but the less common ones are described below and in more detail elsewhere.14 One additional test is appropriate in some cases. Neurologists and other practitioners sometimes refer patients with headaches associated with near vision to clinicians with an Intuitive Colorimeter, to see if precision tinted lenses will be helpful. For adults, particularly if there is significant hypermetropia or Asian ethnicity, it is

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a sensible precaution to check anterior chamber angles with the Van Herick test.35 Angle-closure (include sub-acute and intermittent) can cause symptoms, including blur and photophobia, when reading and, rarely, can affect patients under the age of 40 years36 and very rarely under 20 years.37

What refractive correction should be worn during ocular motor tests? Usually, the purpose of ocular motor tests is to determine the significance of any visual problems that the child may have with schoolwork. So, if the child wears glasses more than 50% of the time when doing schoolwork at the appropriate distance, the child should wear these glasses during ocular motor tests at the same distance. 14 An exception is ocular motility, when spectacles are not usually worn unless there is a very high refractive error, in which case the test should be done with and without glasses.14 It is sometimes useful to repeat some binocular vision tests when a practitioner is proposing making a significant change to the refractive correction (e.g., prescribing glasses for the first time), to check that the new refractive correction is not going to worsen the situation. This can also be sensible if there is a significant chance that the patient may “change” their refractive status, by stopping wearing their glasses. For example, if a hypermetropic child rapidly breaks down to a convergent strabismus without their glasses, then parents should be warned to have a spare pair and to avoid periods without spectacle wear.

Binocular stability assessment, fusional reserves, and vergence facility Binocular instability (Chapter 3) describes a subtle weakness in the co-ordination of the two eyes. The eyes appear to be straight to the

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casual observer and may even be orthophoric on cover testing. However, if a clinician uses a dissociation test (e.g., the Maddox wing), they will detect an excessive degree of instability (e.g., the arrow in the Maddox wing test moves over a large range, such as from 0' to 6') and low fusional reserves. Binocular instability can cause symptoms including double vision, blur, visual perceptual distortions (e.g., words appearing to move) and headaches. One method of investigating binocular stability is to use the fixation disparity test on the near Mallett Unit (Figure 10.3). An advantage of this test is that it mimics the everyday situation when a person is reading. This is different from many orthoptic tests that create artificial conditions, such as dissociation tests that present completely different images to each eye. With the Mallett test, the test itself (O X O in Figure 10.3) and the surrounding text is seen normally by both eyes together, so the eyes have the usual stimulus to align. Only the two green strips are seen by individual eyes, and a subtle misalignment (less than one degree of arc) indicates the patient may be struggling to keep the eyes aligned in everyday life.14 In addition to the questions regarding the alignment of the green (Nonius) lines whilst the patient fixates the “X”, a supplementary question “Do one or both lines ever move?” should be asked.38 In the clinic, any movement of one of the green lines should be investigated by determining the minimum prisms (base-in for an exo-slip) that eliminates the instability, starting with 0.5'.14 The Mallett fixation disparity test has good sensitivity (75%) and specificity (78%) for detecting symptomatic heterophoria.39 Although these values for sensitivity and specificity are good, they are less than 100%, as is the case with most clinical tests. The algorithm in Table 3.2 is designed with this in mind and highlights the importance of combining tests and of measuring fusional reserves.

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Figure 10.3. Mallett Near Vision Fixation Disparity Test, which is used to determine the aligning prism (associated heterophoria) or aligning sphere. Fusional reserves should be assessed at near using a prism bar or phoropter.14 A prism bar is probably the best method because the patient’s eyes can be observed. Base-out prism is used to measure the convergent fusional reserve and base-in prism to measure the divergent fusional reserve. The fusional reserve that opposes the heterophoria should be measured first (i.e., convergent reserve for exophoria).40 The patient is asked to fixate a detailed target while the clinician increases the prism strength before one eye. The prism power is gradually increased (approximately 1' per second) with the power being recorded when the target first becomes blurred (blur point, which may not exist), becomes double or moves to the side (break point), and then as the prism power is reduced, when the target becomes single again (recovery point).14 If the amplitude (from divergent to convergent break points) is less than 20Δ then the patient may have binocular instability (Chapter 3).14 If the fusional reserve is less than twice the heterophoria it opposes then the patient may have decompensated heterophoria (Sheard’s criterion).

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Figure 10.4. Prism flipper, as used to measure vergence facility. Another test that may provide useful information on the vergence system is to assess the rate at which a person can change their vergence. A monocular flipper (Figure 10.4) or binocular flippers can be used.14 If binocular instability or decompensated heterophoria appear to be causing symptoms, they should be treated.14 The main approaches to treatment (fusional reserve exercises, spheres, prisms) are described in Chapter 3.14 The Mallett unit is useful not only for diagnosing these conditions, but also for determining the prism (aligning prism) or sphere that may alleviate the condition when this mode of correction is favoured. The decision about whether to correct or treat a patient is considered in Chapter 3 and again towards the end of this chapter.

Accommodative lag Accommodation is routinely assessed by measuring the amplitude of accommodation. The conventional method is to use a detailed target on a ruler, typically combined in an instrument such as the RAF rule. This test has several limitations that have recently been reviewed. 41 42 An additional test of accommodative function, MEM retinoscopy, is particularly useful in children with reading difficulties because it provides an objective assessment of accommodative accuracy or lag.

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The patient binocularly fixates a detailed target on the retinoscope and is asked to keep this clear. Retinoscopy is carried out along the horizontal meridian and lenses are very briefly held in front of each eye to neutralise the retinoscope reflex. Each lens should only be present monocularly and for a split second so as not to disrupt the status of the

patient's

accommodative

and

binocular

response.

The

accommodative lag is usually about 0.50D, although this is dependent on refractive error43 and refractive error stability.44 Values greater than 1.00D may represent accommodative insufficiency. 14 If a negative lens is required to neutralise the reflex this suggests that the patient may be over-accommodating (accommodative spasm). In a slightly different approach (Nott retinoscopy), the clinician keeps the fixation target in a constant position and moves the retinoscope to and fro to obtain reversal. Typically, this reveals a slightly

lower

degree

of

accommodative

lag.45

Open

field

autorefractors have clinical potential for objectively measuring lag of accommodation,46

47

although this approach is not widely used

clinically at present.

Accommodative facility

Figure 10.6. Accommodative facility testing using binocular flippers

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The ability to alter accommodation rapidly and accurately is called accommodative facility and this can be assessed using ±2.00DS accommodative flippers. The flipper consists of a pair of +2.00DS lenses mounted on one side of a flipper bar and a pair of -2.00DS lenses mounted on the opposite side (Figure 10.6). The patient fixates a near target (at 40cm) while the optometrist alters the accommodative stimulus by placing either the plus lens pair (stimulus of 0.50D) or the negative lens pair (stimulus of 4.50D) in front of the patient’s eyes. The test should always begin with the +2.00DS lenses. The patient reports when the near target is seen clearly after each alteration in accommodative stimulus, with the optometrist counting the number of times clarity is obtained in one minute. This number divided by two gives the accommodative facility rate in cycles per minute. Ideally, a suppression

check

measurements.

14

should

be

included

for

any

binocular

The OXO letters and Nonius lines on a near Mallett

Unit can be used in conjunction with the polarising filters for binocular accommodative

facility

testing.

The

vertical

OXO

target

is

recommended because the patient is less likely to be distracted by movement of the Nonius markers than if the horizontal OXO target is used. Normative values for children and young adults are sometimes given as 11 cycles per minute for monocular facility and 8 cycles per minute for binocular facility. But these figures are based on the work of Zellers and colleagues,48 who reported that this was the mean value in a normative study. Usual practice is to define the normal range of test results as the range within which 95% of results lie. As a rule of thumb, this is the mean ±2 standard deviations (SDs). The standard deviation of Zellers et al.’s data was 5, so the mean ± 2 SDs is a very

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wide range. This may be because the test is confounded by many variables other than accommodative facility, such as refractive error, 49 verbal response, attention, and interpretation of blur. The limitations of the test mean that caution is necessary in interpreting the results. If there are no symptoms, it would seem unwise to base treatment on poor performance with the accommodative facility test at just one appointment. However, if a patient reports difficulty copying from the board and performs poorly at accommodative facility, treatment would seem reasonable. A study in student volunteers demonstrated that objective measures of accommodative function were highly correlated with the subjective responses of persons undergoing the accommodative facility test.50 Patients with low accommodative facility rates may benefit from an accommodative facility training regime in order to improve their dynamic accommodation function.51

Coloured filters If symptoms or reading difficulties persist after the detection and treatment of any significant refractive and/or ocular motor problems, then practitioners should investigate the effect of coloured filters. It is best, whenever possible, to test the patients in lighting conditions that simulate those when they are experiencing the symptoms. Note that lighting conditions in school often are far brighter than the recommended level of 300-500lux. The lighting is usually fluorescent and 80% of schools continue to be lit with low frequency fluorescent lighting that emits 100Hz flicker .52 As noted in Chapteor 8, preliminary evidence may link such lighting with visual stress.

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Figure 10.7. The Intuitive Overlays in use.

With children, testing usually starts by screening with coloured overlays, although with adults this stage is sometimes bypassed (see below). There are several systems of overlays available in the UK. In chronological order of their introduction these are (1) the Intuitive Overlays (iOO Sales Ltd, London, UK); (2) the Cerium Overlays (Cerium Visual Technologies Ltd, Tenterden, UK); (3) Crossbow Overlays and Reading Rulers (Crossbow Education Ltd, Stafford, UK). (The Irlen overlays are only available to Irlen licensees): As explained in Chapter 9, the Intuitive Overlays (Figure 10.7) comprise a set of coloured overlays that have been designed to sample colours systematically53 and which are of an adequate size to be effective545 and have a sufficient range of colours.55 The set consists of twenty A5 sized overlays (two sets of ten different coloured overlays).

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One surface of the overlay has a matte finish whereas the other side is gloss. Chapter 9 provides details of the merits and demerits of each system. The Intuitive Overlays have been used in many research studies, many of which were included in a review by Evans and Allen.56

Procedure for overlay assessment The procedure for assessment with Intuitive Overlays is described in the test instructions. It is always worth confirming the consistency of the chosen overlay or overlay combination. If the patient consistently chooses a particular overlay or combination of overlays, it is possible to measure the effects of the overlays on reading speed (see below) – this can be a helpful indicator of whether the overlay is likely to be used. A computerised version of the coloured overlay test is also available (Thomson Software Solutions, Hatfield, UK), and this includes the Wilkins Rate of Reading Test (see below). Whether this provides a colour suitable for overlays has not been evaluated in published research. Coloured overlays are a rapid and easy method of screening for a benefit from colour, but they have some limitations. If a person benefits from a coloured overlay, they are likely to find precision tinted lenses more helpful. This is because precision tinted lenses can be individually prescribed with greater precision and also help for writing, computer use, and whiteboards as well as reading. Owing to colour adaptation, a person’s optimal colour of precision tint is likely to be different to the optimal colour of overlay (Chapter 9).57 Therefore, the colour for lenses should not be selected as matching that for overlays. Precision tinted lenses are typically prescribed on the basis of testing with the Intuitive Colorimeter.58

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As illustrated in Figure 10.1, children are generally only tested with the Intuitive Colorimeter if they pass the Delphi criteria (described below), which usually means they have shown a significant benefit from a coloured overlay. There are two ways of determining if a person is benefiting from an overlay. The first approach (‘sustained use’) is to dispense the child an overlay to use for a few weeks and invite them to return for testing with the colorimeter if the child, parent, and/or teacher feel that the overlay is helping. An alternative approach is to test the immediate effect of the coloured overlay on the child’s performance. The most common method of doing this is to use the Wilkins Rate of Reading Test (WRRT), which is described below. Practitioners need to be flexible and to be prepared to use each of these methods of determining whether to progress to testing with the colorimeter. For some children the main benefit from the overlay is in a reduction of perceptual distortions, so the WRRT may be the best approach. For others, the main benefit from the overlay is in visual comfort, so the sustained use approach will work best. An objection is sometimes raised about using overlays to determine who will benefit from precision tinted lenses. This is that both the investigative tool that is being used to determine suitability for an intervention and that intervention are very similar – in essence, different forms of coloured filters. It should be noted, in other conditions a treatment is sometimes used in diagnosis (e.g., in decompression sickness).59-61 Similarly, within optometry Elliott advocated that “You can view prescribing glasses as a diagnostic tool”.62 It is important to be mindful of placebo effects, but in visual stress, it is easier to be assured of a genuine response. This is because, a child might expect that the colour lens that should help them most would match the coloured overlay they have chosen, which would in fact arouse suspicions in the clinician (see Chapter 9).57 Nonetheless, it

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is reassuring that an additional diagnostic test exists, the Pattern Glare Test (PGT), which is described later in this chapter.

Procedure for the Wilkins Rate of Reading Test (WRRT) The WRRT63 consists of 10 simple words arranged in random order and in small closely spaced font (Figure 10.5). The patient reads the text as quickly as possible, whilst trying to avoid any mistakes. The test method is described in the test instructions. In summary, the patient reads four versions of the test in the following order: with the intervention (typically, coloured filter), without the intervention, without the intervention, with the intervention. Each time, the practitioner scores the numbers of words correctly read in one minute, calculating the mean performance with the intervention and the mean without the intervention. From this, the effect of the intervention can be calculated in absolute (number of words per minute faster or slower with the intervention) or relative (percentage increase or decrease in speed with the intervention) terms.

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come see the play look up is cat not my and dog for you to the cat up dog and is play come you see for not to look my you for the and not see my play come is look dog cat to up dog to you and play cat up is my not come for the look see play come see cat not look dog is my up the for to and you to not cat for look is my and up come play you see the dog my play see to for you is the look up cat not dog come and look to for my come play the dog see you not cat up and is up come look for the not dog cat you to see is and my play is you dog for not cat my look come and up to play see the

Figure 10.8. The Wilkins Rate of Reading Test.

The Pattern Glare Test Chapter 8 discussed the mechanism for the benefit from coloured lenses and noted that the most likely explanation relates to a hyperexcitability of the visual cortex. As explained in Chapter 8, hyperexcitability is likely to result in sensitivity to certain patterns.64 This pattern glare can be detected with the Pattern Glare Test. With this very simple test, the patient describes their symptoms (in answer to a list of questions) whilst viewing each of three patterns, and their responses indicate their susceptibility to pattern glare. The test can be useful for determining the cases most likely to benefit from coloured filters.65 66

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Figure 10.9. The Pattern Glare Test. The test comprised three patterns, instructions, and a simple scoring system. Only one of the patterns (that most likely to cause symptoms) is shown. Note that the third pattern is no longer thought to be clinically useful.72

The Pattern Glare Test comprises three gratings of differing spatial frequencies (SFs): low (Pattern 1), medium (Pattern 2), and high

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(Pattern 3). A normative study of the Pattern Glare Test showed that people have an abnormal degree of pattern glare if they achieve a score of >3 on the medium grating or a score of >1 when the score for the high SF pattern is subtracted from the score for the medium pattern.67 Such people are likely to benefit from coloured filters. 65 In clinical practice, the high SF grating often is not used and the cut-off for the medium SF grating is the most commonly used criterion. The low SF control grating is useful because it is unlikely that symptoms with this grating will occur. If patients report more than one or two symptoms with this grating, it is likely that they are suggestible and their response with the medium grating is less trustworthy.

Computerised screening for visual stress A comprehensive computerised system for screening for visual stress was developed and evaluated by Singleton and Henderson.68 This Visual Stress Screener can be used in association with a visual stress questionnaire. Thomson Software Solutions supply a system for prescribing coloured filters called ReadEZ Screening Software. However, this does not seem to have been described or evaluated in the scientific literature (PubMed search, January 2022).

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The Intuitive Colorimeter

Figure 10.10. Coloured trial uses used in conjunction with the Intuitive Colorimeter. Note that the small lenses on the spectacles shown would need to be carefully fitted to ensure that the entire visual field is covered. Generally, larger lenses are preferable for use in tinted spectacles.

The Intuitive Colorimeter, described in Chapter 9, is an instrument that illuminates a page of text with coloured light, and it can be used to prescribe individually specific tinted lenses. It enables independent variation in hue (colour) and saturation (depth of colour) without an associated change in luminance (brightness). One major advantage of the Colorimeter compared with overlays is that the variation in colour is continuous rather than in discrete steps. The entire visual field is stimulated with coloured light, as when tinted spectacles are worn. The design of the colorimeter system is described in Chapter 9 and detailed instructions are provided in the instrument manual. The results

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obtained with the Intuitive Colorimeter are checked and refined using precision tinted lenses. At the end of this testing, the patient can look at text with and without their chosen precision tinted lens combination and asked to report on the difference that the tints make to their perception of text. Adults can decide, based on this, whether they think that it is worthwhile to have a pair of precision tinted spectacles made up. Adults with symptoms that are typical of visual stress usually find the effect of precision tinted lenses self-evident. This is why, a screening stage with overlays is often unnecessary with adults.

Prescribing advice for precision tinted lenses It is important that the chosen spectacle eye size is sufficiently large to ensure that the wearer is always looking through the precision tinted lenses. Children should be advised to wear their precision tinted lenses for schoolwork, including homework, if they find them helpful. For adults, they are likely to be helpful for office work and reading. Often users find them valuable for computer use, sometimes for television, and for environments where there are high levels of fluorescent lighting, such as supermarkets. But patients should be advised not to wear them outdoors as sunglasses since they are not likely to protect the eyes from sunlight. Precision tinted lenses should usually not be worn when driving or riding a bicycle, if they are likely to impair the perception of traffic signals. The computer program that is provided with the colorimeter allows practitioners to check this, and safety for use in daylight, for the rare cases where a patient may wish to wear the lenses constantly (e.g., migraine sufferer). The wearing of any tint for driving at night is not recommended. Even if the program indicates that perception of traffic signals should be normal, patients should wear the glasses as a

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passenger under a range of lighting conditions to check this themselves.

Follow-up colorimetry It was noted in Chapter 9, sometimes patients wear their tints for a period and then cease to wear them because the symptoms remit. Children should not be encouraged to wear tinted glasses if they say the glasses are no longer helpful. More frequently, however, symptoms return after a period of time even with continued use of the spectacles, and a revised tint is usually successful in giving a further period of remission. The necessary change in tint can be substantial, but more frequently it is relatively slight. A change in tint is more common in the young: adults rarely need to change the colour. In two open trials, 80% of patients were still wearing their tints when followed up one year after first provision,69 which agrees with the results of a clinical audit.6 Sometimes the need for precision tinted lenses reduces over the years and this may relate to a finding of reduced pattern glare in older people,67 which could indicate reduced cortical hyperexcitability with age. Irlen claimed that 6% of people with visual stress cannot be helped by coloured filters.8 This claim has not been systematically investigated, but if the cortical hyperexcitability explanation for visual stress (Chapter 8) is correct then it is feasible that occasional patients will be encountered for whom no colour is particularly helpful. Similarly, there are likely to be many patients whose visual stress symptoms are not completely alleviated by precision tinted lenses. Other approaches that may be helpful for these cases were discussed in Chapter 9.

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When to treat or correct Binocular vision anomalies only require treatment if they are causing symptoms, impairing performance, or are likely to worsen if left untreated.14 In some cases, it can be difficult to determine whether these criteria are met. With refractive errors, the situation is simpler because the proposed correction can be introduced in a trial frame and demonstrated to the patient. This is appropriate for older children and adults and, as already noted, this approach can be taken with adults after colorimetry. The proposed correction can be demonstrated with trial precision tinted lenses and the patient asked if they find it helpful enough to warrant spectacles. With children, this approach could lead to over-prescribing and so diagnostic criteria for visual stress are generally applied before colorimetry is considered. These diagnostic criteria will now be discussed.

Diagnostic criteria for visual stress There are several possible reasons why a child might choose a coloured filter, and these are summarised in Figure 10.11. Some of the conditions in Figure 10.11can be excluded following the detailed eye examination outlined in this chapter. In addition to this, the clinician should determine if there are positive signs of visual stress, as detailed below.

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Figure 10.11. Possible reasons why children might choose a coloured overlay on first testing. LCA, longitudinal chromatic aberration. The white boxes represent reasons for which there is a physiological explanation, and the grey boxes have psychogenic mechanisms. Reproduced from Evans & Allen (2016)56 under Creative Commons open access. In 2017, Evans, Allen and Wilkins66 used a type of research called a Delphi study70 to canvass the opinion of a group of top prescribers of precision tinted lenses in the UK on the diagnostic criteria for visual stress. Some of the findings were as the researchers anticipated, and indeed as they had taught on courses. However, other findings represented an evolution of diagnostic criteria, revealing convergent opinions amongst practitioners in different regions of the UK. For example, the researchers were interested to find that respondents favoured stricter cut-off criteria for the Wilkins Rate of Reading Test than had hitherto been used.66 This cut-off, of a 15% improvement in the Rate of Reading Test with an overlay, was also indicated in two independent studies published after the Delphi study data were collected.71 72 The diagnostic criteria produced by the Delphi study are summarised in Table 10.2.

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Table 10.2. Putative diagnostic indicators* of visual stress from Evans et al (2017).66

*WRRT, Wilkins Rate of Reading Test; PGT, Pattern Glare Test. The diagnostic criteria in Table 10.2 are labelled putative because, ideally, they would be investigated in prospective clinical trials. However, to date they represent the best attempt at defining criteria for the diagnosis of visual stress. It should be noted, Evans et al stressed that before considering a diagnosis of visual stress, eye care practitioners must seek to exclude other explanations for the symptoms and signs in Table 10.2. Recently, Gilchrist and colleagues have carried out further analysis of Wilkins Rate of Reading Test data to determine the minum criteria for change.73 Their results are broadly in agreement with the 15% criterion, although they preferred to use the absolute value of words correctly read per minute (wcpm) rather than percentage improvement. Their preferred criterion was 22 wcpm, which equates to~13% for a typical adult and ~21% for a typical child.73

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Funding and finding an appropriate practitioner The most accepted mainstream intervention for children with reading difficulties is specialist teaching, ideally in small groups or on a one-to-one basis.74 This is justified since the main contributor to the commonest decoding.

75

reading

difficulty,

dyslexia,

is

poor

phonological

Some children with reading difficulties or other specific

learning difficulties will also have visual problems. In exceptional cases, children may be mis-diagnosed as having reading difficulties when in fact all they need is a visual intervention. In the authors’ opinion, the most common visual problem in people with reading difficulties is visual stress, but before this can be diagnosed practitioners need to rule out a variety of other visual disorders (Figure 10.1). This requires a detailed eye examination which, including the testing for coloured filters, typically takes about an hour. For community optometrists in the UK, this detailed investigation will not be covered by the NHS sight test fee. There are very few secondary care NHS hospitals that currently fund precision tinted lens testing. It is unfortunate that the most people who need this testing and precision tinted lenses currently must fund this themselves, and many of the patients who are in most need cannot afford to pay. College of Optometrists guidance concerning examining patients with specific learning difficulties is to “ensure you have the necessary training in the techniques required to examine patients with these difficulties”.10 Not all eye care practitioners will have the expertise and equipment to carry out these detailed investigations of children with reading difficulties. But within the professions of optometry, orthoptics, and (to a lesser extent) ophthalmology there are practitioners who have specialised in assessing and treating visual factors that can affect reading and learning. Parents, teachers, and educational psychologists often ask how they can find such a specialist

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practitioner in their area and in response to this question an organisation was established in 2007 called the Society for Coloured Lens Prescribers.

Society for Coloured Lens Prescribers The Society for Coloured Lens Prescribers is an internet-based organisation, found at www.s4clp.org. It is a not-for-profit voluntary body that is independent: it is not funded by any commercial organisation and does not charge for membership. S4CLP is a multidisciplinary society that aims to encourage a high level of care from practitioners specialising in this field. Members have consented to abide by a code of conduct which ensures that they have appropriate training, expertise, and equipment. A list of members of the Society is published at www.s4clp.org for the public and education professionals so that they can find practitioners who can provide expert advice on coloured filters and prescribe these when appropriate. The code of conduct states that members will adopt an evidencebased approach and will only prescribe coloured lenses after a full eye examination to detect other relevant conditions. The society is multidisciplinary, with membership open to optometrists, orthoptists, opticians, ophthalmologists, psychologists, and teachers. Practitioners can join through individual membership, where the practitioner (typically an optometrist) provides for all the visual needs of people who might need coloured filters. Practitioners can also join the society as part of a team who together provide for the visual needs of people who might need coloured filters.

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Reference 1. Leslie S. Tinted lenses: Australasian College of Behavioural Optometrists, 2016. 2. General Optical Council. Standards of practice for optometrists and dispensing opticians. London: General Optical Council, 2016. 3. Rowe E, Evans BJW. Are commonplace optometric activities evidence-based? Optometry in Practice 2018;18(4):207-18. 4. Sackett DL, Rosenberg WM, Gray JA, et al. Evidence based medicine: what it is and what it isn't. BMJ 1996;312(7023):71-2. 5. Satterfield JM, Spring B, Brownson RC, et al. Toward a transdisciplinary model of evidence-based practice. Milbank Q 2009;87(2):368-90. doi: 10.1111/j.1468-0009.2009.00561.x 6. Evans BJW, Patel R, Wilkins AJ, et al. A review of the management of 323 consecutive patients seen in a specific learning difficulties clinic. Ophthal Physiol Opt 1999;19(6):454-66. 7. Lightstone A, Evans BJW. A new protocol for the optometric management of patients with reading difficulties. Ophthal Physiol Opt 1995;15(5):507-12. 8. Irlen H. Reading by the Colors: Overcoming Dyslexia and Other Reading Disabilities by the Irlen Method. New York: Avery 1991. 9. Evans BJW, Drasdo N. Tinted lenses and related therapies for learning disabilities - a review. Ophthal Physiol Opt 1991;11:206-17. 10. College of Optometrists. Guidance for professional practice. Professional excellence in eye health. London: College of Optometrists, 2018. 11. O'Leary CI, Evans BJW. Criteria for prescribing optometric interventions: literature review and practitioner survey. Ophthal Physiol Opt 2003;23:42939. 12. Shneor E, Evans BJ, Fine Y, et al. A survey of the criteria for prescribing in cases of borderline refractive errors. J Optom 2016;9(1):22-31. doi: 10.1016/j.optom.2015.09.002 13. Darko-Takyi C, Khan NE, Nirghin U. A review of the classification of nonstrabismic binocular vision anomalies. Optometry Reports 2016;6(5626):1-7. 14. Evans BJW. Pickwell's Binocular Vision Anomalies. Sixth ed. Philadelphia: Elsevier 2021. 15. Harle DE, Evans BJ. Subtle binocular vision anomalies in migraine. Ophthalmic Physiol Opt 2006;26(6):587-96. 16. Lambooij M, Fortuin M, Ijsselsteijn W, et al. Measuring visual fatigue and visual discomfort associated with 3-D displays. Journal of the Society for Information Display 2010;18(11):931-43. 17. Yammouni R, Evans BJW. Is reading rate in digital eyestrain influenced by binocular and accommodative anomalies? J Optom 2021;14(3):229-39. doi: 10.1016/j.optom.2020.08.006 [published Online First: 2020/10/30] 18. College of Optometrists. F02: Guidance for the issuing of small prescriptions and making small changes to existing prescriptions. www

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college-optometrists org 2012 5/16/2012. http://www.collegeoptometrists.org/en/professional-standards/Ethics_Guidance/index.cfm. 19. O'Leary CI, Evans BJW, Edgar DF. The effect of low refractive corrections on rate of reading. Optometry in Practice 2014;15(3):87-100. 20. CITT-ART Investigator Group. Treatment of Symptomatic Convergence Insufficiency in Children Enrolled in the Convergence Insufficiency Treatment Trial-Attention & Reading Trial: A Randomized Clinical Trial. Optom Vis Sci 2019;96(11):825-35. doi: 10.1097/opx.0000000000001443 [published Online First: 2019/10/28] 21. Scheiman M, Denton C, Borsting E, et al. Effect of Vergence/Accommodative Therapy on Reading in Children with Convergence Insufficiency: A Randomized Clinical Trial CITT-ART Investigator Group. Optometry and Vision Science 2019;96(11):836-49. doi: 10.1097/OPX.0000000000001442 22. Evans BJW, Busby A, Jeanes R, et al. Optometric correlates of Meares-Irlen Syndrome: a matched group study. Ophthal Physiol Opt 1995;15(5):481-87. 23. Evans BJW, Wilkins AJ, Brown J, et al. A preliminary investigation into the aetiology of Meares-Irlen Syndrome. Ophthal Physiol Opt 1996;16(4):28696. 24. Scott JC, McWhinnie H, Taylor L, et al. Coloured overlays in schools: orthoptic and optometric findings. Ophthal Physiol Opt 2002;22:156-65. 25. Sheedy J, Hayes J, Engle J. Is all asthenopia the same? Optom Vis Sci 2003;81(11):732-39. 26. Wilkins AJ, Baker A, Amin D, et al. Treatment of photosensitive epilepsy using coloured glasses. Seizure 1999;8(8):444-9. doi: 10.1053/seiz.1999.0337 [published Online First: 2000/01/11] 27. Evans BJW, Patel R, Wilkins AJ. Optometric function in visually sensitive migraine before and after treatment with tinted spectacles. Ophthal Physiol Opt 2002;22:130-42. 28. Marasini S, Khadka J, Sthapit P, et al. Ocular morbidity on headache ruled out of systemic causes----A prevalence study carried out at a community based hospital in Nepal. Journal of Optometry 2012 doi: 10.1016/j.optom.2012.02.007 29. Dotan G, Stolovitch C, Moisseiev E, et al. Uncorrected amteropia among children hospitalized for headache evaluation: a clinical descriptive study. BMC Pediatr 2014;14:241. doi: 10.1186/1471-2431-14-241 30. Hendricks TJ, J. DB, van Der Horst FG, et al. Relationship between habitual refractive errors and headache complaints in schoolchildren. Optom Vis Sci 2007;84(2):137-43. doi: 10.1097/OPX.0b013e318031b649 [doi];00006324200702000-00013 [pii] 31. Headache Classification Committee of the International Headache Society (IHS) The International Classification of Headache Disorders (ICHD), 3rd edition. Cephalalgia 2018;38(1):1-211. doi: 10.1177/0333102417738202 32. Wilkins AJ. Visual Stress. Oxford: Oxford University Press 1995. 33. Loew SJ, Watson K. A prospective genetic marker of the visual perceptual disorder Meares-Irlen Syndrome. Perceptual and Motor Skills 2012;114(3):870-82.

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34. Robinson GL, Foreman PJ, Dear KBG. The familial incidence of symptoms of scotopic sensitivity/irlen syndrome. Perceptual and Motor Skills 1996;83:1043-55. 35. Campbell P, Redmond T, Agarwal R, et al. Repeatability and comparison of clinical techniques for anterior chamber angle assessment. Ophthalmic Physiol Opt 2015;35(2):170-78. doi: 10.1111/opo.12200 [doi] 36. Ritch R, Chang BM, Liebmann JM. Angle closure in younger patients. Ophthalmology 2003;110(10):1880-9. doi: 10.1016/S0161-6420(03)00563-3 [published Online First: 2003/10/03] 37. Gao F, Wang J, Chen J, et al. Etiologies and clinical characteristics of young patients with angle-closure glaucoma: a 15-year single-center retrospective study. Graefes Arch Clin Exp Ophthalmol 2021 doi: 10.1007/s00417-021-05172-6 [published Online First: 2021/04/21] 38. Karania R, Evans BJ. The Mallett Fixation Disparity Test: influence of test instructions & relationship with symptoms. Ophthal Physiol Opt 2006;26:507-22. 39. Jenkins TCA, Pickwell LD, Yekta AA. Criteria for decompensation in binocular vision. Ophthal Physiol Opt 1989;9:121-25. 40. Rosenfield M, Ciuffreda KJ, Ong E, et al. Vergence adaptation and the order of clinical vergence range testing. Optom Vis Sci 1995;72(4):219-23. 41. Burns DH, Evans BJW, Allen PM. Clinical measurement of amplitude of accommodation: a review. Optometry in Practice 2014;15(3):75-86. 42. Burns DH, Allen PM, Edgar DF, et al. Sources of error in clinical measurement of the amplitude of accommodation. J Optom 2020;13(1):314. doi: 10.1016/j.optom.2019.05.002 43. Gwiazda J, Thorn F, Bauer J, et al. Myopic children show insufficient accommodative response to blur. Invest Ophthalmol Vis Sci 1993;34(3):6904. [published Online First: 1993/03/01] 44. Allen PM, O'Leary DJ. Accommodation functions: co-dependency and relationship to refractive error. Vision Res 2006;46(4):491-505. doi: S00426989(05)00245-2 [pii];10.1016/j.visres.2005.05.007 [doi] 45. Cacho P, Garcia-Munoz A, Garcia-Bernbabeu G, et al. Comparison between MEM and Nott dynamic retinoscopy. Optom Vis Sci 1999;76(9):650-55. 46. Allen PM, Radhakrishnan H, O'Leary DJ. Repeatability and validity of the PowerRefractor and the Nidek AR600-A in an adult population with healthy eyes. Optom Vis Sci 2003;80(3):245-51. doi: 00006324-200303000-00014 [pii] 47. Mallen EA, Wolffsohn JS, Gilmartin B, et al. Clinical evaluation of the ShinNippon SRW-5000 autorefractor in adults. Ophthalmic Physiol Opt 2001;21(2):101-7. [published Online First: 2001/03/23] 48. Zellers JA, Alpert TL, Rouse MW. A review of the literature and a normative study of accommodative facility. J Am Optom Assoc 1984;55(1):31-74. 49. O'Leary DJ, Allen PM. Facility of accommodation in myopia. Ophthalmic Physiol Opt 2001;21(5):352-55. doi: S0275-5408(01)00002-3 [pii]

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50. Allen PM, Charman WN, Radhakrishnan H. Changes in dynamics of accommodation after accommodative facility training in myopes and emmetropes. Vision Res 2010;50(10):947-55. doi: S0042-6989(10)00124-0 [pii];10.1016/j.visres.2010.03.007 [doi] 51. Sterner B, Abrahamsson M, Sjostrom A. The effects of accommodative facility training on a group of children with impaired relative accommodation - a comparison between dioptric treatment and sham treatment. Ophthal Physiol Opt 2001;21(6):470-76. 52. Winterbottom M, Wilkins A. Lighting and visual discomfort in the classroom. J Environ Psychology 2007;29:63-75. 53. Wilkins A. Overlays for classroom and optometric use. Ophthal Physiol Opt 1994;14:97-99. 54. Waldie M, Wilkins A. How big does a coloured overlay have to be? Ophthal Physiol Opt 2004;24:57-60. 55. Smith L, Wilkins A. How many colours are necessary to increase the reading speed of children with visual stress? A comparison of two systems. Journal of Research in Reading 2007;30(3):332-43. 56. Evans BJW, Allen PM. A systematic review of controlled trials on visual stress using Intuitive Overlays or the Intuitive Colorimeter. Journal of Optometry 2016;9(4):205-18. 57. Lightstone A, Lightstone T, Wilkins A. Both coloured overlays and coloured lenses can improve reading fluency, but their optimal chromaticities differ. Ophthal Physiol Opt 1999;19(4):279-85. 58. Wilkins AJ, Nimmo-Smith I, Jansons JE. Colorimeter for the intuitive manipulation of hue and saturation and its role in the study of perceptual distortion. Ophthal Physiol Opt 1992;12:381-85. 59. Rudge FW. A case of decompression sickness at 2,437 meters (8,000 feet). Aviat Space Environ Med 1990;61(11):1026-7. 60. Rudge FW. Decompression sickness affecting the temporomandibular joint. Aviat Space Environ Med 1990;61(12):1139-40. 61. Spira A. Diving and marine medicine review part II: diving diseases. J Travel Med 1999;6(3):180-98. 62. Elliott DB. Refraction and prescribing. In: Elliott DB, ed. Clinical procedures in primary eye care. Fourth ed. Oxford: Elsevier 2014:68-111. 63. Wilkins AJ, Jeanes RJ, Pumfrey PD, et al. Rate of Reading Test: its reliability, and its validity in the assessment of the effects of coloured overlays. Ophthal Physiol Opt 1996;16(6):491-97. 64. Wilkins A, Nimmo-Smith I, Tait A, et al. A neurological basis for visual discomfort. Brain 1984;107:989-1017. 65. Hollis J, Allen PM. Screening for Meares-Irlen sensitivity in adults: can assessment methods predict changes in reading speed? Ophthalmic Physiol Opt 2006;26(6):566-71. 66. Evans BJW, Allen PM, Wilkins AJ. A Delphi study to develop practical diagnostic guidelines for visual stress (pattern-related visual stress). Journal of Optometry 2017;10(3):161-68.

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67. Evans BJW, Stevenson SJ. The Pattern Glare Test: a review and determination of normative values. Ophthal Physiol Opt 2008;28:295-309. 68. Singleton C, Henderson LM. Computerized screening for visual stress in children with dyslexia. Dyslexia 2007;13(2):130-51. 69. Maclachlan A, Yale S, Wilkins A. Research note: open trial of subjective precision tinting. Ophthal Physiol Opt 1993;13:175-78. 70. Mishra C, Tripathy K. Commentary: Delphi method in ophthalmology: The guiding principles from experienced minds for ambiguous clinical situations. Indian J Ophthalmol 2021;69(11):3319-20. doi: 10.4103/ijo.IJO_2608_21 [published Online First: 2021/10/29] 71. Garcia ACO, Momensohn-Santos TM, Vilhena DA. Effects of Spectral Overlays on Reading Performance of Brazilian Elementary School Children. Folia Phoniatr Logop 2017;69(5-6):219-25. doi: 10.1159/000484139 72. Wilkins AJ, Allen P, Monger LJ, et al. Visual stress and dyslexia for the practising optometrist. Optometry in Practice 2016;17(2):103-12. 73. Gilchrist J, Allen P, Monger L, et al. Precision, reliabilty and application of the Wilkins Rate of Reading Test. Ophthalmic and Physiological Optics 2021;41 doi: 10.1111/opo.12894 74. Strayhorn JM, Bickel DD. A randomized trial of individual tutoring for elementary school children with reading and behavior difficulties. Psychol Rep 2003;92(2):427-44. 75. White S, Milne E, Rosen S, et al. The role of sensorimotor impairments in dyslexia: a multiple case study of dyslexic children. Dev Sci 2006;9(3):23755.

Chapter 11 Other potential uses of precision tints

Chapter abstract In this chapter we review studies in which precision tints have been used in a variety of neurological disorders, including photosensitive epilepsy, autism, migraine, cluster headache, visual snow, stroke, multiple sclerosis and concussion. Whilst the evidence regarding these topics is preliminary and indicative rather than conclusive, the effects of coloured filters in these conditions may help to further elucidate the mechanisms underlying the benefit from colour. In particular, the extent to which these findings provide convergent support for the cortical hyperexcitability hypothesis is discussed.

Photosensitive epilepsy Photosensitive epilepsy is a condition in which seizures are provoked by flickering light. It is usually diagnosed with the help of the electroencephalogram (EEG), which shows a particular configuration of waveforms, known as a photoparoxysmal response, when the patient is exposed to flickering light. Over the years there have been many studies of the effect of the colour of the light that provokes this response. In their review, Harding and Jeavons1 (pp 57-61) cite 17 studies, some showing greater effects of red light and some showing little difference between light of various colours. Many patients with photosensitive epilepsy are sensitive not only to flickering light but also The original version of this chapter was revised: The correction to this chapter is available at https://doi.org/10.1007/978-3-031-03930-0_13 © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022, corrected publication 2022 A. J. Wilkins and B. J. W. Evans, Vision, Reading Difficulties, and Visual Stress, https://doi.org/10.1007/978-3-031-03930-0_11

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to patterns.2 To see whether precision tints might offer symptomatic relief,

Wilkins

and

colleagues3

examined

33

patients

with

photosensitive epilepsy. Twenty-three (70%) reported beneficial perceptual effects of coloured light in the Intuitive Colorimeter and were given precision tints to wear. The chromaticities of the tints are shown in Figure 11.1. They transmitted 29.9% of the light on average. Seventeen of the 23 patients were contacted after an average of 2.4 years. Thirteen of the 17 (76%) were still wearing the tinted glasses and reporting reduced symptoms. There were reduced seizures in three patients, some of whom received changes in antiepileptic medication during this period. One patient, however, had no change in medication over the course of five years and the reduction in her seizures was unequivocal, see Figure 11.2.

Figure 11.1 Chromaticities of lenses selected by patients with photosensitive epilepsy. The large points represent lenses that were of particular benefit. The Compare the distribution of chromaticities to that in Figure 8.1.From Reference 3.

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Figure 11.2 For one patient who appeared to receive a marked benefit from precision tinted lenses, the number of seizures every 3-month period before and after blue glasses became available. From Reference 3.

Autism Many children with autism spectrum disorder (ASD) have a sensory sensitivity. A series of studies has revealed how coloured filters can reduce this sensitivity and thereby improve the perception of emotion. The first study, conducted by Ludlow et al4 used the Intuitive Overlays.5 Nineteen school children with a diagnosis of autism (aged 8-15 years) and a control group of 19 typically developing children (matched for age and intelligence) selected an overlay of a colour that improved the clarity of text.

Eleven of the children with autism increased their

reading speed on the Wilkins Rate of Reading Test by more than 15%. An increase of this size was seen in only two children in the control group. Subsequent work by Fong and colleagues6 has failed to find any effect of coloured overlays in children with autism, but their task involved reading digits arranged in a widely spaced matrix.

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In a subsequent study Ludlow et al7 placed overlays over a page of text and asked children to select those that improved the clarity of text. The overlays were then placed over a plain sheet of paper and the children were asked which colour they preferred. The overlays selected for clarity increased reading speed in the autism group but not the control group, as in the earlier study, but overlays chosen on the basis of colour preference had no beneficial effect on reading speed in either group. The beneficial effect of the overlays was not confined to reading. The task of matching objects to samples of similar objects, see Figure 11.3, was also improved with an overlay chosen to improve the clarity of text.

Figure 11.3. Examples of stimuli in a matching to sample task. From Reference 6

The Mind in the Eye task8 has been widely used to measure ‘theory of mind’ in individuals with autism. It presents pictures of just the eyes of a face (Figure 11.4) and requires the observer to make a judgement as to which of four adjectives best describes the emotion the face is expressing.

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Figure 11.4. A face from the Mind in the Eye task. Reproduced with permission from Simon Baren-Cohen Ludlow et al9 administered this task to 15 children with autism spectrum disorders aged 8-17 and a control group matched individually for age and sex. The test was given with and without overlays having a colour selected as improving the clarity of text. The children with autism performed more poorly than the typically developing children, but their performance was improved with the overlay. The extent of improvement in recognizing the emotion correlated with the increase in reading speed that the overlay afforded. Whitaker et al10 corroborated and extended these findings using a task that required holistic judgement of facial expression. Sixteen children with autism spectrum disorder were asked to judge which of two faces expressed the stronger emotion, a task that requires observation of the eyes and the mouth. The images were presented side by side in shades of grey on a computer screen. The screen was either white or tinted a shade of colour chosen previously as improving the clarity of text. The discrimination was better when the screen was coloured. There were no such effects for a control group of typically developing children matched for age and intelligence. The above findings were examined in a more realistic setting by Ludlow et al11 using the Emotion Evaluation Test, in which professional actors enact ambiguous scripts recorded in video and representing seven basic emotions: happy, surprised, sad, angry, anxious, revolted (and

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neutral, not used in this study). The video sequences are in colour, and they portray naturalistic complex expressions with appropriate intonation and gestural cues. A series of statements is offered and the viewer has to endorse or reject each. Fourteen children with autism spectrum disorder and fourteen typically developing children matched for intelligence took part. Initially the participants were examined with the Intuitive Colorimeter12 and a combination of tinted trial lenses was selected matching the chosen settings (active tint). A computer was used to compute a combination of trial lenses with a difference in chromaticity of 0.07 (control tint), a difference that has repeatedly been shown to eliminate beneficial effects of a selected colour 13, see Figure 11.5. (a)

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(b)

Figure 11.5 Chromaticities of lenses chosen for clarity by (a) children with ASD and (b) with typical development (TD) connected by lines to the chromaticities of lenses with control colour. From Reference 10.

One month later the children watched two versions of the Emotion Evaluation Test, one when wearing the active tint and the other when wearing the control tint, in random order. The mean number of emotions correctly identified is shown in Figure 11.6. The tint improved performance of the children with ASD to the level of the typically developing children.

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Figure 11.6. Mean number of emotions identified in the Emotion Evaluation Test using placebo and chosen (active) tint for ASD and typically developing (TD) children. Bars show standard deviations. *p < .05; ***p < .001. From Reference 10

Ludlow et al11 also administered the Social Inference-minimal test (SI-M) in which vignettes of actors make sincere or sarcastic statements. It requires the viewer to detect the sarcasm based on the demeanour of the actors, such as their tone of voice, facial expression or gestures. For comparison the test includes sincere verbal exchanges (five vignettes) in which the targeted speakers mean what they are saying; i.e., the words spoken, and the paralinguistic cues are consistent with this meaning. In the simple sarcasm exchanges (five vignettes), the literal meaning is contrary to the spoken message but this can only be determined by reading the paralinguistic cues, such as facial expression, voice prosody (rhythm) and hand and body posture. The content of the verbal script for both the sincere exchange and simple sarcasm exchange could be similar: “I’d be happy to do it. I’ve got plenty of time” might be an example script for

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either. Paradoxical sarcasm is also included in which the behaviours were not consistent with the verbal expression. Participants were asked to endorse or reject statements about what a specific actor was doing, saying, thinking, and feeling. The results mirrored those of the Emotion Evaluation Test as shown in Figure 11.7.

Figure 11.7. Mean number of sarcasm exchanges identified in the SI-M using placebo and chosen tint for children with ASD and those that were typically developing (TD). Bars show standard deviations. **p