Practical Visual Electrophysiological Examination 9811689091, 9789811689093

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Practical Visual Electrophysiological Examination Ruifang Sui Fu Tang Minglian Zhang

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Practical Visual Electrophysiological Examination

Ruifang Sui • Fu Tang • Minglian Zhang

Practical Visual Electrophysiological Examination

Ruifang Sui Department of Ophthalmology Peking Union Medical College Hospital Beijing, China Minglian Zhang Department of Ophthalmology Hebei Eye Hospital Xingtai, China

Fu Tang Roland Consult Stasche & Finger GmbH Brandenburg, Germany Gaush Medical Group Beijing, China

Reviewer: Dezheng Wu Department of Fundus Image and Function Guangzhou Aier Eye Hospital Guangzhou, China

ISBN 978-981-16-8909-3    ISBN 978-981-16-8910-9 (eBook) https://doi.org/10.1007/978-981-16-8910-9 © People’s Medical Publishing House, PR of China 2022 Jointly published with People’s Medical Publishing House, PR of China The print edition is not for sale in China (Mainland). Customers from China (Mainland) please order the print book from: People’s Medical Publishing House, PR of China. This work is subject to copyright. All rights are reserved by the Publishers, whether the whole or part of the material is concerned, specifically the rights of 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 publishers, 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 publishers nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publishers remain neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

Visual electrophysiology has been applied in clinical practice for more than 70 years. Many related books, focusing on detailed principles and clinical cases, have been published worldwide. However, this monograph aims to cover the elementary theory of visual electrophysiology practice for clinicians, researchers, and technicians. The contents include the concept of the visual electrophysiological, hardware composition, standardized operation and clinical cases, with step-by-step explanation and hand-to-hand guidance. All follow the international standards of ISCEV. Typical examples are highlights of this book, which can help physicians and technicians quickly understand the meaning underlying different waveforms. In addition, visual electrophysiology studies on animals are also involved in this book. The clinical cases listed in the book are from Peking Union Medical College Hospital and Hebei Eye Hospital. Professor Dezheng Wu was invited to review the book, and we are grateful to her. We hope this “desk book” provides a valuable reference of fundamental visual electrophysiological application for clinicians, technicians, and researchers. What we’ve done still leaves much to be desired. Suggestions and comments are welcome. Timely revision and supplements will be made to the book when it is reprinted. Beijing, China Beijing, China  Xingtai, China 

Ruifang Sui Fu Tang Minglian Zhang

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Contents

1 Visual Electrophysiology Summary ����������������������������������������������   1 1.1 Visual Electrophysiology Basic Mechanism and Features������   1 1.1.1 Basic Principle������������������������������������������������������������   1 1.1.2 Clinical Importance����������������������������������������������������   1 1.2 Classification of Visual Electrophysiology ����������������������������   2 1.2.1 Basic Classification����������������������������������������������������   2 1.2.2 Classification of Traditional Visual Electrophysiology ������������������������������������������������������   2 1.2.3 Classification of Multifocal Visual Electrophysiology ������������������������������������������������������   2 1.3 Visual Electrophysiology Clinical Application Principles��������������������������������������������������������������������������������   2 1.3.1 Overall Check ������������������������������������������������������������   2 1.3.2 Combined with Other Clinical Results ����������������������   3 1.3.3 Binocular Contrast������������������������������������������������������   3 1.4 Visual Electrophysiology International Standards������������������   3 1.4.1 ISCEV Standards��������������������������������������������������������   3 1.4.2 Revision of the ISCEV Standards������������������������������   4 1.4.3 The Relation Between the Book and ISCEV Standards��������������������������������������������������������������������   4 2 Visual Electrophysiology Examination Equipment����������������������   5 2.1 Visual Electrophysiology Hardware Compositions����������������   5 2.2 Visual Electrophysiology Stimulators������������������������������������   5 2.2.1 Stimulator Classification��������������������������������������������   5 2.2.2 Full-Field Ganzfeld����������������������������������������������������   5 2.2.3 Graphic Stimulator������������������������������������������������������   6 2.2.4 Stimulators for Infants������������������������������������������������   7 2.3 Visual Electrophysiology Electrodes��������������������������������������   9 2.3.1 Skin Electrode������������������������������������������������������������   9 2.3.2 Corneal Electrode ������������������������������������������������������  10 3 Visual Electrophysiology Result Reading Key Points������������������  13 3.1 Visual Electrophysiology Result Reading Principles ������������  13 3.1.1 The Form, Influencing Factors, and Characteristics of Visual Electrophysiological Examination Results ��������������������������������������������������  13

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3.1.2 Result Reading Key Points of Visual Electrophysiological Examination������������������������������  14 3.2 VEP Basic Features and Report Reading Key Points ������������  15 3.2.1 VEP and EEG ������������������������������������������������������������  15 3.2.2 Role and Classification of VEP����������������������������������  15 3.2.3 VEP Application Range and Stimulation Mode ��������  15 3.2.4 PVEP Versus FVEP����������������������������������������������������  17 3.2.5 VEP Scope of Application������������������������������������������  17 3.2.6 Examples of VEP Clinical Reports and Key Points of Reading Diagrams ��������������������������������������  18 3.3 ffERG Basic Features and Report Reading Key Points����������  22 3.3.1 ffERG Basic Process and Signal Origin ��������������������  22 3.3.2 ffERG Active Electrode Selection������������������������������  24 3.3.3 ffERG Basic Waveform����������������������������������������������  25 3.3.4 ffERG New International Standard Changes��������������  26 3.3.5 ffERG Normal and Abnormal Waveform Contrast ����  26 3.3.6 ffERG Clinical Features����������������������������������������������  29 3.3.7 ffERG Scope of Application ��������������������������������������  30 3.3.8 Examples of Normal ffERG Clinical Report and Key Points of Reading the Diagram��������������������  30 3.3.9 Examples of Abnormal ffERG Clinical Report and Key Points of Reading the Diagram��������������������  33 3.4 PERG Basic Features and Report Reading Key Points����������  36 3.4.1 PERG Basic Process and Its Clinical Significance����  36 3.4.2 PERG Waveform��������������������������������������������������������  37 3.4.3 PERG Scope of Application ��������������������������������������  37 3.4.4 Examples of Normal PERG Clinical Reports and Key Points of Reports Reading����������������������������  38 3.4.5 Examples of Abnormal PERG Clinical Report and Key Points of Reading the Diagram��������������������  38 3.5 mfERG Basic Features and Report Reading Key Points��������  38 3.5.1 mfERG Basic Concept������������������������������������������������  38 3.5.2 Three ERGs Comparisons������������������������������������������  41 3.5.3 Scope of Application for mfERG ������������������������������  41 3.5.4 Examples of Normal mfERG Clinical Reports and Key Points of Reading ����������������������������������������  44 3.5.5 Examples of Clinical Reports of mfERG Abnormalities and Key Points of Image Reading������  46 3.6 EOG Basic Features and Report Reading Key Points������������  46 3.6.1 EOG Recording Process and New Changes in International Standards ����������������������������������������������  46 3.6.2 Application Scope of EOG ����������������������������������������  46 3.6.3 Examples of Normal EOG Clinical Reports and Key Points of Reading ����������������������������������������  46 3.6.4 Examples of Abnormal EOG Clinical Reports and Key Points of Reading ����������������������������������������  46

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4 Visual Electrophysiology Clinical Cases����������������������������������������  53 4.1 Visual Electrophysiology Examination Selections and Application Scope������������������������������������������������������������  53 4.1.1 Visual Electrophysiology Examination Selections Protocol ����������������������������������������������������  53 4.1.2 Application Scope of Visual Electrophysiology ��������  53 4.2 Optic Neuropathy��������������������������������������������������������������������  54 4.2.1 Optic Nerve Demyelination����������������������������������������  54 4.2.2 Degeneration of the Optic Nerve��������������������������������  54 4.3 ROP����������������������������������������������������������������������������������������  55 4.4 Inherited Retinopathy��������������������������������������������������������������  56 4.4.1 Stargardt’s Disease������������������������������������������������������  56 4.4.2 Bull’s Eye Maculopathy ��������������������������������������������  56 4.4.3 Best Vitelliform Macular Dystrophy��������������������������  58 4.4.4 Congenital Stationary Night Blindness����������������������  59 4.4.5 X-Linked Juvenile Retinoschisis��������������������������������  59 4.4.6 Retinitis Pigmentosa ��������������������������������������������������  60 4.4.7 Occult Macular Dystrophy ����������������������������������������  64 4.5 Acquired Retinopathy ������������������������������������������������������������  64 4.5.1 Diabetic Retinopathy��������������������������������������������������  66 4.5.2 Central Retinal Artery Occlusion��������������������������������  75 4.5.3 Central Retinal Vein Occlusion����������������������������������  75 4.5.4 Macular Hole��������������������������������������������������������������  81 4.5.5 Age-Related Macular Degeneration ��������������������������  81 4.5.6 Acute Zonal Occult Outer Retinopathy����������������������  85 4.6 Toxic Retinopathy ������������������������������������������������������������������  85 4.7 Refractive Media Opacity ������������������������������������������������������  85 4.8 Glaucoma��������������������������������������������������������������������������������  85 4.8.1 Glaucoma Steady-State PERG ����������������������������������  90 4.8.2 Glaucoma Transient-State PERG ������������������������������  90 4.8.3 Glaucoma PhNR ERG������������������������������������������������  90 4.9 Amblyopia������������������������������������������������������������������������������  92 4.10 Eye Diseases Judicial Expertise����������������������������������������������  92 4.11 Eye Diseases Visual Electrophysiological Examinations Selection����������������������������������������������������������������������������������  93 5 Visual Electrophysiology Equipment Install and Operation ������ 101 5.1 Visual Electrophysiology Equipment Install�������������������������� 101 5.1.1 Installation of Ground Wires�������������������������������������� 101 5.1.2 Inspection Room Requirements and Layout�������������� 101 5.2 PVEP Operation Steps and Key Points���������������������������������� 102 5.2.1 PVEP Examination for Adult�������������������������������������� 103 5.2.2 PVEP Examination for Children�������������������������������� 106 5.3 FVEP Operation Steps and Key Points���������������������������������� 109 5.3.1 FVEP Examinations for Adult������������������������������������ 109 5.3.2 FVEP Examinations for Infant and Young Children���������������������������������������������������������������������� 109 5.4 ffERG Operation Steps and Key Points���������������������������������� 110 5.4.1 ffERG Electrode Operation Points and Notes������������ 110 5.4.2 Prepare Before ffERG Examination �������������������������� 112

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5.4.3 ffERG Examination Operation Steps�������������������������� 112 5.4.4 ffERG Result Analysis and Marker Adjustment�������� 112 5.4.5 ffERG Examination for Infants and Young Children���������������������������������������������������� 119 5.5 PERG Operation Steps and Key Points���������������������������������� 120 5.5.1 Prepare Before PERG Examination���������������������������� 120 5.5.2 PERG Electrode Operation Key Points���������������������� 120 5.5.3 PERG Examination Stimulus Conditions������������������ 122 5.5.4 PERG Examination Operation Steps�������������������������� 123 5.5.5 PERG Examination for Children�������������������������������� 123 5.6 mfERG Operation Steps and Key Points�������������������������������� 123 5.6.1 Prepare Before mfERG Examination ������������������������ 123 5.6.2 mfERG Electrode Requirements�������������������������������� 124 5.6.3 mfERG Operating Essentials�������������������������������������� 124 5.6.4 mfERG Steps�������������������������������������������������������������� 124 5.7 EOG Operation Steps and Key Points������������������������������������ 125 5.7.1 Preparation Before EOG Examination ���������������������� 125 5.7.2 EOG Electrode Requirements������������������������������������ 126 5.7.3 EOG Operation Steps ������������������������������������������������ 127 5.8 Visual Electrophysiological Examinations Operation Key Points Comparing������������������������������������������������������������ 127 5.9 Different ERG Electrodes Comparing������������������������������������ 127 6 ISCEV Extended Visual Electrophysiological Examinations������ 131 6.1 Objective Visual Acuity-VEP SF Limit���������������������������������� 131 6.2 ON/OFF PVEP����������������������������������������������������������������������� 131 6.3 Three Channels PVEP������������������������������������������������������������ 132 6.4 Three Channels FVEP������������������������������������������������������������ 132 6.5 S-Cone ERG���������������������������������������������������������������������������� 133 6.6 PhNR ERG������������������������������������������������������������������������������ 133 6.7 The Stimulus-Response Series for the Dark-Adapted ffERG�������������������������������������������������������������������������������������� 134 6.8 ON/OFF ERG ������������������������������������������������������������������������ 134 6.9 PERG+PVEP Simultaneous Examination������������������������������ 136 6.10 Multifocal Visual Evoked Potential���������������������������������������� 136 7 Visual Electrophysiological in Animal Experiments�������������������� 145 7.1 Hardware for Animal Visual Electrophysiological Examinations�������������������������������������������������������������������������� 145 7.2 Animal VEP���������������������������������������������������������������������������� 145 7.2.1 Animal PVEP Examination���������������������������������������� 145 7.2.2 Animal FVEP Examination���������������������������������������� 147 7.3 Animal ERG���������������������������������������������������������������������������� 147 7.3.1 Animal Serial Dark Adaptation ffERG Response Examination���������������������������������������������������������������� 148 7.3.2 Animals Light Adaptation ffERG Examination���������� 148 7.3.3 Animals PERG Examination�������������������������������������� 148 7.3.4 Animals mfERG Examination������������������������������������ 148

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7.4 Animal Examination SOP������������������������������������������������������ 152 7.4.1 Animal FVEP Examination SOP�������������������������������� 152 7.4.2 Animal ffERG Examination SOP ������������������������������ 153 7.4.3 Animal mfERG Examination SOP ���������������������������� 154 References ������������������������������������������������������������������������������������������������ 157

About the Authors

Ruifang  Sui, M.D., Ph.D.  Professor, Ophthalmology Department; Division Chief, visual electrophysiology and ophthalmic genetics, Peking Union Medical College Hospital; Principal Investigator, Key Laboratory of Ocular Fundus Disease, Chinese Academy of Medical Sciences; Member of ARVO, AAO, ISCEV, ASHG, and COS. She graduated from West China University of Medical Sciences and later from Peking Union Medical College. She was awarded the fellowship from Helen Keller Eye Research Foundation and engaged at ocular genetics and visual function studies in Iowa University and the National Eye Institute, NIH, USA.  Dr. Sui’s research interest includes retinal degeneration/dystrophy, congenital eye abnormalities, disease gene function, and gene therapy. She is the only Chinese researcher who received the award from Foundation Fighting Blindness. Her team did a large cohort study and genotype–phenotype research on inherited retinal degenerations (IRDs). Collaborated with other teams, her team found eight new genes associated with IRDs. She also has extensive experience in clinical visual electrophysiology and genetic counseling. Recently, she received Huaxia Medical Science and Technology Award and China Medical Science and Technology Award.

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About the Authors

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Fu  Tang, M.D., M.Sc.  Product specialist in Gaush Medical Group; Director of Visual Electrophysiology Department; Vice General Manager of Roland Consult Stasche & Finger GmbH; ISCEV member. He graduated from Beijing Medical University in 1999 and joined Gaush in 2004. He has been in charge of product training, market promotion, and pre-sales and after-sales service of Roland visual electrophysiology and Kowa series fundus cameras. He possesses rich knowledge of Roland visual electrophysiological products, clinical operation and related clinical applications. He participated in the compilation and translation of “Roland Visual Electrophysiology Test Methods and Clinical Application Atlas” edited by professor Dezheng Wu. In addition, he edited an internal training book “Guidelines for the Clinical Application of Standard Visual Electrophysiology with Roland system,” which was printed 8 times and published over 2000 copies. He organized more than 50 visual electrophysiology training courses and workshops. He is also a lecturer in the Roland global distributors training and user training courses. Minglian  Zhang, M.D.  Professor and Dean of Hebei Eye Hospital; Director of Key Ophthalmic Laboratory of Hebei Province; Vice President of Xingtai Association for Science and Technology. He is a deputy director for academic societies and a co-editor for several books and journals. He has 35 years of clinical experience in ophthalmology, visual electrophysiological examination, and traditional Chinese medicine and especially in the treatment of complicated ocular fundus diseases, uveitis, and dry eye with combined western medicine and traditional Chinese medicine. He developed several new Chinese herbs formula and was awarded patents. He also won several provincial science and technology progress awards and was funded by National Natural Science Foundation. More than one hundred papers were published by his team. He gained Hebei Province outstanding professional and technical personnel honour.

List of Abbreviations

AMD Age-related macular degeneration AZOOR Acute zonal occult outer retinopathy BVMD Best vitelliform macular dystrophy CRT Cathode ray tube CSNB Congenital stationary night blindness DOA Kjer-type dominant optic atrophy DR Diabetic retinopathy EEG Electroencephalogram EOG Electrooculogram ERG Electroretinogram FFA Fundus fluorescein angiography ffERG Full-field electroretinogram FVEP Flash visual evoked potential ISCEV International Society for Clinical Electrophysiology of Vision LCD Liquid crystal display LED Light-emitting diode LHON Leber hereditary optic neuropathy mfERG Multifocal electroretinogram mfVEP Multifocal visual evoked potential NAION Nonarteritic anterior ischemic optic neuropathy OMD Occult macular dystrophy ON/OFF ERG On/off electroretinogram ON/OFF PVEP Onset/offset pattern VEP PERG Pattern electroretinogram PhNR Photopic negative response PVEP Pattern visual evoked potential RP Retinitis pigmentosa RPE Retinal pigment epithelium S-Cone Short cone SLO Scanning laser ophthalmoscope STR Scotopic threshold response VEP Visual evoked potential XLRS X-linked juvenile retinoschisis

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1

Visual Electrophysiology Summary

1.1

Visual Electrophysiology Basic Mechanism and Features

1.1.1 Basic Principle Visual electrophysiological examination is applied to record the bioelectrical signals from different parts of the visual pathway after the subject’s visual system receives a stimulation, such as a flash or a pattern. Assorted electrodes are used to collect the bioelectrical signals and then waveforms are processed by biological amplifiers and computers (Fig. 1.1).

1.1.2 Clinical Importance Visual electrophysiology is an objective test of visual function, which can assess retinal and optic nerve functions. Visual electrophysiological examination is widely used in the clinic, and abnormal waveform may reflect ocular disease conditions. Besides, some retinal and optic disorders have specific changes. However, the diagnosis of diseases should be based on the electrophysiological examinations and combine the clinical manifestation and other ophthalmological data. For children who could not cooperate with the subjective visual functional

Fig. 1.1  Schematic diagram of visual electrophysiological examination testing and recording

© People’s Medical Publishing House, PR of China 2022 R. Sui et al., Practical Visual Electrophysiological Examination, https://doi.org/10.1007/978-981-16-8910-9_1

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1  Visual Electrophysiology Summary

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test or those who do not cooperate reasonably with the trauma evaluation, electrophysiology of vision is the only way to objectively measure the visual function without the subjective cooperation of the examinee. It is challenging to make a precise diagnosis of a variety of hereditary retinopathy, such as congenital stationary blindness and achromatopsia. Visual electrophysiological examination is one of the diagnostic criteria. Visual electrophysiological assessment can guide treatment and prognosis prediction for retinal vascular diseases, such as diabetic retinopathy. Moreover, visual electrophysiological examination plays an irreplaceable role in the diagnosis and follow-up of optic neuropathy, such as acute optic neuritis and multiple sclerosis. Furthermore, visual electrophysiology can also be used for screening for early glaucoma and preoperative retinal function assessment for cataracts.

1.2

Classification of Visual Electrophysiology

1.2.1 Basic Classification According to the time of clinical application, software, hardware, and calculation methods, visual electrophysiology is generally divided into two groups: traditional visual electrophysiology and multifocal visual electrophysiology. Traditional visual electrophysiology includes electroretinogram (ERG), visual evoked potential (VEP), and electrooculogram (EOG). The phrase “traditional visual electrophysiology” appeared after the birth of multifocal visual electrophysiology. In order to distinguish from multifocal visual electrophysiology, the original visual electrophysiology was classified as traditional electrophysiology (also called conventional electrophysiology). Multifocal visual electrophysiology contains multifocal electroretinogram (mfERG) and multifocal visual evoked potential (mfVEP).

1.2.2 Classification of Traditional Visual Electrophysiology According to different stimulating methods, VEP and ERG in traditional electrophysiological are divided into two types: flash (flash electroretinogram, FERG; flash visual evoked potential, FVEP) and pattern (pattern electroretinogram, PERG; pattern visual evoked potential, PVEP). EOG is induced by eye movement with two fixation points without stimulus and therefore no further classification. ERG mainly reflects the function of the retina. FERG, also known as full-field electroretinogram (ffERG), reveals the massive function of the retina. ffERG is the international standard name for flash ERG, which is used in this book. PERG reflects macular photoreceptor and ganglion cell function. VEP demonstrates the whole visual pathway’s function. EOG exhibits the function of retinal pigment epithelium and retinal photoreceptor cells.

1.2.3 Classification of Multifocal Visual Electrophysiology Both mfERG and mfVEP require particular stimulators and software programs. The mfERG assesses the local ERG from different regions of the central retina. The mfVEP enables simultaneous recording from multiple regions of the visual field. However, due to significant variation, it is rarely used in clinical practice. The above Sects. 1.2.1, 1.2.2 and 1.2.3 classification are shown in Fig. 1.2.

1.3

Visual Electrophysiology Clinical Application Principles

1.3.1 Overall Check The visual electrophysiological examination should be as comprehensive as possible. Each

1.4  Visual Electrophysiology International Standards

3

visual electrophysiology

Traditional visual electrophysiology

electroretinogram (ERG)

Mutilfocal visual electrophysiology

electrooculogram (EOG)

visual evoked potential (VEP)

full-field electroretinogram (ffERG)

pattern electroretinogram (PERG)

the function of the overall retina

macula and ganglion cell function

pattern visual evoked potential (PVEP)

the functions of retinal pigment epithelium and retinal photoreceptor cells

multifocal electroretinogram (mfERG)

multifocal visual evoked potential (mfVEP)

the focal function of macula

objective field of vision

flash visual evoked potential (FVEP) the whole visual pathway’s function

Fig. 1.2  Schematic diagram of visual electrophysiological classification

examination item has its unique value and cannot be substituted for each other. At present, PVEP and FVEP are commonly used for visual electrophysiological examination. PVEP and FVEP generally are recommended at least twice as repetitions. If there is good repeatability, then it is reliable. FVEP has a significant variation, which is only detected in patients with poor vision and unable to cooperate to the gaze fixation point. In addition, FVEP itself has significant variation, which requires more repeatable results than PVEP to support the corresponding conclusions. If necessary, it can be used to determine whether the results are abnormal or not based on high-frequency steady-state FVEP. Highfrequency steady-state FVEP refers to the FVEP with stimulus frequency greater than 7 Hz, and its amplitude value is stable with small variation. ffERG is also widely used and reflects more clinical information. mfERG is used to evaluate retinal function in macular-related diseases.

1.3.2 C  ombined with Other Clinical Results Visual electrophysiological examination results should be combined with clinical symptoms and other ophthalmic or general examination results

for analysis. The results of the visual electrophysiological examination are the results of retinal or optic nerve function evaluation, which are sometimes inconsistent with other clinical manifestations and require comprehensive analysis and judgment by clinicians.

1.3.3 Binocular Contrast Visual electrophysiological examination results vary greatly, and every examination should be binocular control, which is more objective and convenient than the reference value control. If the difference of double eyes’ visual electrophysiological result is more than 30%, the worse eye will be considered abnormal, and even the result is within the normal reference range.

1.4

Visual Electrophysiology International Standards

1.4.1 ISCEV Standards Founded in 1958, the International Society for Clinical Electrophysiology of Vision (ISCEV) is an authoritative academic organization for Vision Electrophysiology. The association’s primary function is to develop and update the international

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standards of visual electrophysiology examination regularly and hold the international academic conference of visual electrophysiology once per year to promote the standardization of examination results of different equipment and different examination rooms. So far, ISCEV has published the international standards of ERG, VEP, PERG, EOG, and mfERG, respectively, and specified the inspection methods and parameters. Each examination room shall conduct each clinical examination under the above standardized international standards so that the results of different examination rooms may be cross-referenced. ISCEV website is https://iscev.wildapricot.org, information about the association introduction, a variety of standards and conferences can be downloaded free of charge. ISCEV’s official academic journal is Documenta Ophthalmologica, https://link. springer.com/journal/10633. Most of the documents can be downloaded for free for ISCEV members.

1.4.2 Revision of the ISCEV Standards The ISCEV ERG standard was first formulated in 1989 and then revised five times in 1994, 1999, 2004, 2008, and 2015. The first edition of the ISCEV VEP standard was developed in 2004, and it has been revised twice since 2009 and 2016. In 1996, ISCEV released the PERG guide-

1  Visual Electrophysiology Summary

lines, which were upgraded to the first version of the standard in 2000, and then revised twice in 2007 and 2012. The first edition of the ISCEV EOG standard was formulated in 1993 and revised in 1998, 2006, 2010, and 2017. ISCEV mfERG developed the guideline in 2003, revised them into the second edition guideline in 2007, and upgraded them to the first edition standard in 2011, and in 2021, the second edition standard was published.

1.4.3 T  he Relation Between the Book and ISCEV Standards Examination items specified in international standards are clinical essential examination items, and operation steps of Chap. 5 of the book “visual electrophysiological equipment installation, operation steps” are written following the latest standard. In the book, the concept, naming, examination items, and application scope are also based on the latest edition of the standard to make results more scientific, more accurate, and more convenient. On this basis, each examination room can also carry out special extended examination items other than those in international standards according to their clinical and scientific research needs. These special examination items are also mentioned in the above ISCEV standards and the several related extended protocols in 2018 and 2019.

2

Visual Electrophysiology Examination Equipment

2.1

Visual Electrophysiology Hardware Compositions

The visual electrophysiology diagnostic apparatus for both traditional and multifocal visual electrophysiology examination consists of a complete set of hardware, including main control computer, flash stimulator, graphic stimulator, biological signal amplifier, isolation power box, and various electrodes. Figure 2.1 is the visual electrophysiological examination equipment composition diagram. The flash stimulator can emit flash stimulations for ffERG and FVEP, and there are two LED lamps built inside of the flash stimulator for EOG examination fixation guidance. Graphic stimulators emit pattern stimulations for PVEP and PERG, and high brightness pattern stimulation for mfERG and mfVEP.  The fixation surveillance camera of the flash stimulator is located inside, for the graphic stimulator is located in the front. A biological signal amplifier is a key component of visual electrophysiology, which can effectively shield interfering noise signals and amplify useful signals. Generally, the two-channel amplifier is enough, while a four-channel amplifier is suitable for special examination as three-­channel VEP (see Chap. 6) and mfVEP.

2.2

Visual Electrophysiology Stimulators

2.2.1 Stimulator Classification Visual electrophysiological stimulators include flash stimulators and graphic stimulators. The flash stimulators include full-field Ganzfeld for adults, flat-lay full-field stimulators and various handheld flash stimulators for infants and bed rest patients, and flash stimulators for animal experiments. The graphic stimulators include adult graphic stimulators, handheld graphic stimulators for children, and scanning laser ophthalmoscope (SLO) stimulator. The new SLO stimulators can be used in clinical examination and animal experiments.

2.2.2 Full-Field Ganzfeld 2015, ISCEV ERG standard states that the fullfield Ganzfeld stimulator must be able to provide a uniformly bright flash stimulus for the entire visual field [1]. Ganzfeld stimulators are usually implemented with domed or fully spherical designs, which require a uniform, smooth, and white spherical reflector. Different colors of lightemitting diodes (LED) are normally used as the

© People’s Medical Publishing House, PR of China 2022 R. Sui et al., Practical Visual Electrophysiological Examination, https://doi.org/10.1007/978-981-16-8910-9_2

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2  Visual Electrophysiology Examination Equipment

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graphic stimulator flash stimulator control monitor

camera for monitor biosignal amplifer isolation power box main control computer

Fig. 2.1  Hardware composition of visual electrophysiological examination equipment

common flashlight source, and the Xenon lamp is used as the high-intensity flashlight source. The opening surface of the sphere shall cover the binocular or the whole head of the adult and shall be equipped with a lower jaw bracket and a frontal bracket to fix head position and keep the patient comfortable. The Ganzfeld stimulator has a builtin infrared camera to monitor eye position.

2.2.3 Graphic Stimulator According to different kinds of stimulator luminescence materials, graphics stimulators can be classified as cathode ray tube (CRT), liquid crystal display screen (LCD), LED, SLO, and other different types.

2.2.3.1 CRT Graphic Stimulator CRT graphic stimulator is the most commonly used graphic stimulator from 1980 to 2010. Its linearity scanning light has a latency time of upper and lower parts more than 10  ms, which

Fig. 2.2  CRT graphic stimulator

can be made up by software (Fig. 2.2). It was the most cost-effective graphic stimulator at that time, but it was discontinued worldwide in 2010.

2.2  Visual Electrophysiology Stimulators

Fig. 2.3  LED graphic stimulator

2.2.3.2 LED Graphic Stimulator LED graphic stimulator is an ideal graphic stimulator with synchronous scanning, no delay, stable brightness, and strong intensity (Fig.  2.3). But the cost is too high to be commercialized. 2.2.3.3 LCD Graphic Stimulator According to different kinds of backlit sources, LCD graphics stimulators can be classified as cold cathode fluorescent lamps (CCFL) backlit LCD and LED backlit LCD. The illumination of the CCFL backlit LCD is uneven, which is not suitable for the graphic stimulators. LED-backlit LCD has uniform brightness, and can be used as a graphic stimulator. LED-backlit LCD graphic stimulator (Fig. 2.4) has the highest cost performance and can be used for clinical PVEP, PERG, mfERG, and mfVEP tests. 2.2.3.4 SLO Graphic Stimulator SLO graphic stimulator adopts a laser light source with uniform brightness, which can provide ON/OFF light without delay, and the infrared laser light source can monitor the fundus in

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Fig. 2.4  LED backlit LCD graphic stimulator

real-time, which is the most ideal graphic stimulator at present. SLO graphic stimulator (Fig. 2.5) can be used for precise counterpoint and stimulating of PVEP, PERG, and mfERG examinations in clinical and animal experiments. SLO graphic stimulator can realize accurate fixation under confocal laser fundus surveillance, to complete human and animal PVEP, PERG, and mfERG examinations.

2.2.4 Stimulators for Infants 2.2.4.1 The Stimulator Used for Infants and Bedridden Patients The full-field Ganzfeld flash stimulator for adults can also be used for examination of infants and other bedridden patients, which require a holder to rotate the stimulator to the horizontal position, then it can achieve binocular ffERG and FVEP stimulation for infants and bedridden patients. Children should take the full-field Ganzfeld flash stimulator examination under anesthesia, general anesthesia is  a priority, and sedatives can also be used for

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2  Visual Electrophysiology Examination Equipment vertical position

horizontal position

Fig. 2.5  SLO graphic stimulator

Fig. 2.6  Ganzfeld full-field flash stimulator and rotatable electric standing

anesthesia. After anesthesia, the patient should lay flat to fully meet the international standard requirements for reliable examination results (Fig.  2.6). Full-field Ganzfeld stimulator can be used for binocular synchronization ffERG examination, which is fast and convenient without the need for sequential dark and light adaptation, respectively.

2.2.4.2 Handheld Graphic Stimulator A handheld graphic stimulator (Fig. 2.7) can be used for PVEP and PERG examination of infants. The stimulator can track the eye position of infants, and apply to infants over half a year old. Children can be examined on parents’ arms. 2.2.4.3 Instant Control Babyflash Stimulator Babyflash (Fig.  2.8) stimulator can be used for ffERG and FVEP examination for sober infants and can track the eye position of infants, suitable for infants over half a year old. The Babyflash reflector is flat.

Fig. 2.7  Handheld graphic stimulator

2.2.4.4 Mini-Ganzfeld Handheld Flash Stimulator The stimulator, shown in Fig. 2.9, can be used for monocular ffERG and FVEP stimulation in bedridden patients and infants. Anesthesia is required for examination in children, and the ffERG is required for the monocular examination. Dark and light adaptation examinations are conducted successively in the left and right eyes, respectively. Mini-ganzfeld is a spherical reflector.

2.3  Visual Electrophysiology Electrodes

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Fig. 2.8  Babyflash instant control flash stimulator

Fig. 2.10  Gold cup electrode

2.3.1 Skin Electrode

Fig. 2.9  Mini-Ganzfeld handheld flash stimulator

2.3

Visual Electrophysiology Electrodes

According to the different functions of visual electrophysiological recording, electrodes can be classified as the active electrode, reference electrode, and grounding electrode. The active electrode is placed on the main electrophysiological signal generating location to record positive potential; the reference electrode is placed in areas corresponding to the electrophysiological signal generating location and where can form a complete return potential, and record negative potential, and the grounding electrode is placed away from positive and negative potential to record zero potential. According to the different locations, the electrode can be divided into skin electrodes and corneal electrodes.

2.3.1.1 Gold Cup Electrode or Silver Cup Electrode The gold cup (gold-plated silver chloride) or silver cup (silver chloride) electrodes are generally used for skin electrodes (Fig. 2.10), which both are the most commonly used electrode for visual electrophysiological examination. The active electrode, reference electrode, grounding electrode of VEP and EOG, and the ERG reference electrode and grounding electrode are all skin electrodes. 2.3.1.2 Infant Skin Electrode The special skin electrodes with high viscosity can be used for infants and toddlers (Fig. 2.11), which are not easy to fall off due to the infants’ activities. This electrode can be used only once. 2.3.1.3 Ear Clip Gold or Silver Cup Electrode Ear clip gold or silver cup electrodes (Fig. 2.12) are commonly used for grounding electrodes. This kind of electrode is easy to be installed and not easy to fall off.

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2  Visual Electrophysiology Examination Equipment

Fig. 2.11  Skin electrodes for infants

Fig. 2.13  ERG-Jet corneal contact lens electrode

metal ring electrode, etc.) and bipolar electrodes (Burian Allen electrode, etc.). The bipolar electrode has an active electrode, which can record positive potential and a reference electrode that can record negative potential.

Fig. 2.12  Ear clip gold cup electrode

2.3.2 Corneal Electrode The corneal electrode is a kind of active electrode in ERG examination and is used to record positive potential (except bipolar electrode). Corneal surface anesthesia is required for the examination. Corneal electrodes include positive electrodes (ERG-Jet corneal contact lens electrode, DTL electrode, Gold Foil electrode and HK conductive

2.3.2.1 ERG-Jet Corneal Contact Lens Electrode ERG-Jet corneal contact lens electrode has a ring of gold wire on the contact surface of the cornea as a conductive medium, which should be kept intact during use (Fig.  2.13). This kind of electrode is widely used, stable waveform and amplitude, and its disadvantage is poor tolerance of patients, and difficult to install. It can be used for human and large animal ffERG and mfERG examination. 2.3.2.2 DTL (Dawson, Trick, and Litzkow) Electrode The DTL electrode was well tolerated with slightly lower amplitude, suitable for children, and can be used for human and all animals ffERG, PERG, and mfERG examination.

2.3  Visual Electrophysiology Electrodes

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Fig. 2.14  DTL conductive fiber electrode

Fig. 2.15  Roll-type DTL electrode

2.3.2.2.1  DTL Conductive Fiber Electrode The DTL electrode is a kind of electrode containing nylon and silver as conducting medium (Fig. 2.14). 2.3.2.2.2  Roll-Type DTL Electrode The rolled DTL electrode (Fig.  2.15) is made of the same material as the DTL conductive fiber electrode. Before the examination, it can be cut to the corresponding length according to the width of the patient’s eyelid, and then it can be fixed on the canthus with tape or a special clamp with a line.

2.3.2.3 Gold Foil Electrode The gold foil electrode (Fig. 2.16) is similar to the DTL electrode, and with good tolerance to patients. Gold foil electrode is a soft electrode coated with gold foil, and it is for human and large animal ffERG, PERG, and mfERG examination.

Fig. 2.16  Gold foil electrode

2.3.2.4 HK (Hawlina, Konec) Conductive Metal Ring Electrode The HK conductive metal ring electrode (Fig. 2.17) is similar to the DTL electrode and the gold foil electrode, which is more durable and has good tolerance to patients. The material of the contact surface between HK electrode and lower eyelid is silver, gold, or platinum, and the rest part is made of ferrion. It is for human and large animal ffERG, PERG, and mfERG examination. 2.3.2.5 Burian Allen Electrode (B-A Electrode) B-A electrode (Fig.  2.18) is a bipolar electrode with an eyelid opener, which is classified according to diameters, and the adult electrode diameter

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2  Visual Electrophysiology Examination Equipment

Fig. 2.19  Kooyman electrode

is 22 mm and child electrode diameter is 21 mm. It has a large ERG amplitude and stable outcome without an independent reference electrode. And it is used for human and large animal ffERG and mfERG examination.

Fig. 2.17  HK conductive metal ring electrode

Fig. 2.18  Burian Allen electrode

2.3.2.6 Kooyman Electrode Kooyman electrode (Fig. 2.19) is a kind of electrode with one 4W LED stimulator, and which has two kinds of diameters, 17 mm for children and 20 mm for adults. It can be used for human and large animal ffERG examination.

3

Visual Electrophysiology Result Reading Key Points

3.1

Visual Electrophysiology Result Reading Principles

3.1.1 T  he Form, Influencing Factors, and Characteristics of Visual Electrophysiological Examination Results 3.1.1.1 The Results Presentation Form Most of the results of the visual electrophysiological examination are represented by Fig. 3.1 graph, and the observation indicators include waveform, amplitude, and peak time [1, 2]. 3.1.1.2 Factors Influencing Visual Electrophysiological Examination Many factors affect the visual electrophysiological examination, such as the surrounding electromagnetic environment interference, groundline

connection mode, stimulating conditions, types of the electrode, electrode installation and location, program parameter setting, patient factors (such as the pupil, age and refractive status, whether anesthesia), etc., so each examination room must develop a normal reference value and operating procedures.

3.1.1.3 Characteristics of Visual Electrophysiological Examination There are many kinds of visual electrophysiological examination, different examination items have different waveform characteristics and different observation indexes. The amplitude and peak time should be compared with the normal range of corresponding items. The ISCEV international standard stipulates that each examination room should establish the ERG and VEP reference value for the equipment according to the operating procedure and the patient population. ERG and VEP parameters (such as ffERG b-wave amplitude and PVEP P100 amplitude) are not a normal distribution, and reference values should be defined using median (not mean) and bilateral 90% confidence intervals (i.e., 5 and 95% loci). The ISCEV international standard also stipulates that the printed report should show the normal reference value of each examination, and the patient results should be compared with it for analysis [1].

Fig. 3.1  Basic waveform of visual electrophysiology © People’s Medical Publishing House, PR of China 2022 R. Sui et al., Practical Visual Electrophysiological Examination, https://doi.org/10.1007/978-981-16-8910-9_3

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3  Visual Electrophysiology Result Reading Key Points

3.1.1.3.1  Variation Between the Examination Rooms There is a large variation between different examination rooms, which requires the examination room to establish its normal range based on different interference conditions, different operation habits of operators, different use of electrodes, and other factors.

more convenient than normal reference value control.

3.1.1.3.2  Variation with Age ERG amplitude increases rapidly with age in infants and decreases with age in adults, especially in the elderly. The amplitude of VEP in infants and children under 15 years was more than 50% higher than that in adults, while that in the elderly was relatively lower. So, the reference value needs to be adjusted for age. 3.1.1.3.3  Variation Among Individuals Visual electrophysiology varies widely among individuals, so every examination should be binocular control, which is more meaningful and

3.1.2 R  esult Reading Key Points of Visual Electrophysiological Examination ISCEV standards request that a complete visual electrophysiology report should include the following content (Table 3.1). This chapter mainly introduces the basic principle of visual electrophysiological examination result reading key points, the later chapters will combine the characteristics of every visual electrophysiological examination indexes, introduce normal waveform for each examination indexes, interpret the typical cases of various types of anomaly waveform, and analysis the waveform characteristics, different examination indexes observation elements, clinical significance, and cases reports reading key points.

Table 3.1  ISCEV standards examination report key points Index Stimulating and process Patients Eye Wave name and type

Waveform changing Changes in the number of waves Amplitude and peak time change and extent

Lesions location

Normal range

Content Stimulating sensitivity, amplifier pass bandwidths Type of electrode, pupil condition, anesthesia, and degree of coordination OD or OS Single visual electrophysiological examination should be described separately according to different stimulus conditions, such as PVEP high spatial frequency (15′ visual angel stimulation small squares) and low spatial frequency (60′ visual angel stimulation large squares), and ffERG six indexes should be described respectively, too Waveform normal, abnormal, and the specific shape of the waveform Mainly refers to the quantity change of ERG oscillation potential waves Amplitude change includes amplitude increase and amplitude decrease, amplitude change mainly refers to decrease, while peak time change mainly refers to wave peak delay. Amplitude reduction can be classified as mild, moderate, and severe. Mild reduction means that the measured value is 30% lower than the lower limit of the normal value. Moderate reduction means that the measured value is between 30 and 70% of the lower limit of the normal value. A severe reduction is less than 70% below the lower limit of normal Multifocal electrophysiology can find the location of lesions. For example, mfERG can be analyzed according to concentric circles centering on the macular fovea, or according to quadrants and freely selected areas As mentioned above, the normal range varies greatly between rooms and ages, so the influence of different ages should be considered when reading the result, and different examination rooms should establish their reference range based on age

3.2  VEP Basic Features and Report Reading Key Points

3.2

 EP Basic Features V and Report Reading Key Points

3.2.1 VEP and EEG VEP is a cluster of electrical signals in the occipital cortex of the brain that respond to visual stimuli (flash or pattern stimuli). Both VEP and electroencephalogram (EEG) are bioelectricity produced by the brain’s cortex, and the VEP’s recording technique, similar to EEG, is using electrodes in the right places in the head to record a waveform that includes brain waves. But the VEP and EEG are different, the VEP mainly records special effects to the visual stimulation that is located in the occipital optic center, EEG is spontaneous. The two stimulating ways have a considerable gap of intensity, and record location and the reaction of the VEP amplitude is lower than the EEG, generally within 3–25 μV, so with the single stimulation method, it is difficult to extract the VEP signal from the spontaneous EEG around 100  μV.  VEP requires a regular repeated flash or graphics to stimulate the retina, and averaging superposition computer technology to record the VEP waveforms.

3.2.2 Role and Classification of VEP Normal VEP depends on the conduction function of retinal and optic nerve pathways. When the retina is functional, VEP reflects the conduction of visual signals from the ganglion cells of the retina to the occipital cortex of the brain. According to the stimulus, VEP can be divided into Flash VEP (FVEP) and Pattern VEP (PVEP). The VEP international standard, updated in 2016, describes VEP as an electroencephalogram signal recorded on the scalp of the visual cortex. Electrical activity in the visual cortex is primarily activated by the central visual field, and VEP relies on the integrity of the central visual field of the entire visual pathway, which includes the ocular refractive system (cornea, aqueous chamber, lens, and vitreous body), retina, optic nerve, optic radiations, and occipital cortical areas [2] (Fig. 3.2).

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3.2.3 V  EP Application Range and Stimulation Mode 3.2.3.1 PVEP Application Range and Stimulation Mode PVEP applies to all patients who can cooperate with the examination. Generally, children over 2-years old can be examined. The stimulation pattern adopts a black and white checkerboard pattern of 1° (60′) and 15′. According to the standard inspection distance of 1 m, the corresponding field of vision of the 19-in. pattern stimulator is 17°. PVEP can reflect the function of the macular retina and optic nerve pathway with black and white checkerboard reversal stimulation (Fig. 3.3), the spatial frequency setting is related to the screen size and the checking distance, should be following the ISCEV PVEP standard to select stimulator screen size and the checking distance. PVEP fixation viewpoint should be in the middle of the red cross and not be the solid design, so as not to block the macular center field of vision. There would be a 2-rps (reversals/s), that is 1  Hz, and a minimum of 50 averages. There would be a minimum of two repeats, which would be displayed in the results report [2]. Typical normal PVEP waveform is shown in Fig. 3.4. It is important to note that in the past PVEP is believed to be suitable for patients with vision better than or equal to 0.1, patients with vision less than 0.1, or children who were unable to cooperate PVEP should check with FVEP.  The 2016 ISCEV VEP standard for the VEP examination abolished vision requirements, no matter how much vision is put forward, as long as patients can cooperate, PVEP check first. And FVEP applies to patients who have poor visual acuity or cannot cooperate PVEP examination, in other words, PVEP can also be preferred to patients with a visual acuity less than 0.1 [2]. For subjects with poor fixation, nystagmus and suspected pseudo-blindness, onset/offset pattern VEP (ON/OFF PVEP) can be adopted. The stimulus pattern is a 60′ and 15′ black and white checkerboard and gray background alternating conversion. Typical normal waveforms are shown in Fig. 3.5.

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3  Visual Electrophysiology Result Reading Key Points

Fig. 3.2  Schematic diagram of VEP visual path. The optical signal reaches the retina through the cornea, aqueous chamber, pupil, lens, vitreous, and other refractive systems. The retina converts the optical signal into biological electrical signal, which is then transmitted to the optic nerve. Through the subsequent optic chiasma, optic tract and optic radiations, the optical signal reaches the

optic center of the visual cortex where the visual signal can be perceived. The VEP active electrode is placed in the position of the visual cortex, and the corresponding electrical signal can be collected and recorded to the VEP waveform through the visual electrophysiological biological signal amplifier and computer processing

Fig. 3.4  Typical normal PVEP waveform

Fig. 3.3  PVEP checkerboard pattern

When hemianopsia patients receive a general PVEP examination, due to the examination distance being 1 m, hemianopsia patients will view the figure with the normal vision side, then the PVEP results tend to be in the normal range. Even with the half field PVEP stimulation, this

3.2  VEP Basic Features and Report Reading Key Points

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Fig. 3.5  Onset/offset pattern VEP typical normal waveform

Fig. 3.6  Typical normal waveform of FVEP

kind of patient also could not match the fixation well. In the case of the above situation, the SLO pattern stimulator can be used to realize the accurate fixation inspection of PVEP in the halffield of view.

abnormal PVEP and normal FVEP, and patients with peripheral retinal lesions may show abnormal FVEP and normal PVEP. Table 3.2 compares PVEP and FVEP.

3.2.3.2 PVEP Application Range and Stimulation Mode Full-field Ganzfeld stimulator can be used with FVEP for adults and children older than 2 years. ISCEV standard indicates unnecessary dilation and minimum stimulation range ≥20°. Normal people in the near range of full-field flash stimulation, although there is pupil narrowing, but does not affect the scope of retinal stimulation, still up to 100° or so. The stimulation frequency is 1 Hz, and every single examination should repeat at least 50 times, the minimum number of repeated examinations should be at least 2 times, which should be shown in the result report. FVEP mainly reflects a wide range of retinal and optic pathway functions [2]. Typical normal waveform of FVEP is shown in Fig. 3.6. Children under 2 years can be checked with different types of handheld flash stimulator FVEP depending on the fit.

3.2.5 VEP Scope of Application

3.2.4 PVEP Versus FVEP PVEP and FVEP have different stimulation scopes and different lesion areas, and their examination results may be inconsistent. For example, patients with local macular lesions may show

The clinical application scope of VEP includes the following five types of lesions.

3.2.5.1 Optic Neuropathy VEP is used for the diagnosis and qualitative analysis of optic neuropathy, among which the peak time delay of P100 wave is caused by demyelinating lesions such as multiple sclerosis, which is related to abnormal conduction of optic nerve, while the amplitude reduction is related to neuropathic compression lesions and optic nerve axonal degeneration. 3.2.5.2 Unexplained Loss of Vision VEP can combine ffERG, PERG, and mfERG to localize the lesions causing vision loss. 3.2.5.3 Glaucoma VEP can be used to monitor optic nerve function in patients with glaucoma. 3.2.5.4 Amblyopia VEP can be used in the differential diagnosis of amblyopia, and in the follow up of amblyopia. 3.2.5.5 Refracting Media Opacity VEP can be used to judge the visual function of patients with refractive media opacity.

3  Visual Electrophysiology Result Reading Key Points

18 Table 3.2  PVEP and FVEP comparison Comparison content Stimulate scope

Stimulus frequency Average numbers of single checking Repeat numbers Typical normal figure

Observe indicators Waveform characteristics Clinical significance

Patients

PVEP

FVEP

Macular and peripheral diameter 17° stimulation range 2 rps(reservals/s), 1 Hz

Total retinal stimulation range

≥50

≥50

≥2

≥2

P100 Amplitude and peak time

P2 Amplitude and peak time

The waveform was stable, and the variation between patients and the same patients was small Decreased amplitude reflected optic nerve axonal degeneration and delayed peak time reflected optic nerve conduction abnormality. Decreased amplitude is associated with retinal function in the macular area. The abnormal degree of PVEP amplitudes and peak time is related with the abnormal degree of the disease lesion, specially as the different vision acuity. Patients who can cooperate with fixation [2]

The variation between different patients is large, the waveform difference is large; Repeated tests in the same patient showed less variation Decreased amplitude reflected optic nerve axonal degeneration and delayed peak time reflected optic nerve conduction abnormality. Decreased amplitude is associated with peripheral retinal function. The degree of abnormality in FVEP amplitude and peak time was independent of the degree of abnormality in lesions, especially in different visual acuity. FVEP cannot be used for quantitative analysis, only for qualitative analysis. Poor vision, patients without fixation vision [2]

3.2.6 E  xamples of VEP Clinical Reports and Key Points of Reading Diagrams 3.2.6.1 Normal PVEP Learning and mastering PVEP normal waveform is the basis of graph reading analysis. Therefore, before learning PVEP abnormal waveform reading, it is necessary to understand PVEP normal waveform and basic characteristics (Fig.  3.7). Generally, the reading order of the PVEP diagram is first the right eye, then the left eye, and then the binocular comparison is conducted, and repeatability should be done. If the repeatability is good, which means the peak time and amplitude of

1 Hz

multiple examination results are consistent, then the result is reliable.

3.2.6.2 Abnormal PVEP Examples of abnormal PVEP are shown in Figs. 3.8 and 3.9. 3.2.6.3 Normal FVEP There is a large variation of FVEP between individuals, and different patients have different waveform characteristics, but the consistency of multiple examination results of the same patient is often very good. Therefore, FVEP needs more repeated examinations, and good repeatability means good reliability of the results. Examples of normal FVEP waveforms are shown in Figs. 3.10 and 3.11.

3.2  VEP Basic Features and Report Reading Key Points

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Fig. 3.7  An example of a normal PVEP.  Checked subject, 48 years, the P100 amplitude was >10 μV, the amplitude and peak time of P100 of both eyes PVEP 1° (60′) and 15′ were normal. In 1° and 15′, two spatial frequency of PVEP inspections were in accordance with international standards to repeat testing twice, and the consistency of the amplitudes and peak times of twice inspection results was good, which confirms the results had high reli-

ability. PVEP normal reference values: the P100 amplitude should be >20 μV for children under the age of 15 years, and 7–20  μV for adults; 1° spatial frequency of P100 peak time is about 90–110 ms, 15′ stimulation P100 peak time is 5–10 ms later than one of 1° (In this figure, Normal is the recommended reference value of Roland Consult electrophysiology, and there are some differences among different brands.)

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3  Visual Electrophysiology Result Reading Key Points

Fig. 3.8  Abnormal PVEP example 1 (abnormal right eye). The patient was 65 years old, PVEP showed that the repeatability of the two examinations of the 1° spatial frequency of the right eye was reasonable, the amplitude of P100 was severely reduced, with peak time delay. 15′ spatial frequency twice detection repeatability is poor, no

PVEP waveform induced. The amplitude of P100 of left eye 1° and 15′ spatial frequency are normal, but the peak time of P100 at 15′ spatial frequency is delayed, and the amplitude and peak time of P100 twice check have good repeatability, high reliability

3.2  VEP Basic Features and Report Reading Key Points

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Fig. 3.9  Abnormal PVEP example 2 (binocular abnormality). The patient was 35 years old, and PVEP examination results showed a slight decrease in the P100 amplitude of 1° spatial in the right eye (mean of two repeated amplitudes was taken), with peak time delay. The P100 ampli-

tude of 1° spatial frequency in the left eye decreased slightly, and the peak time was not delayed. P100 amplitudes of Binocular 15′ spatial frequency were moderately lower, without peak time delay. Both tests have good repeatability and reliability

22

3  Visual Electrophysiology Result Reading Key Points

Fig. 3.10  Normal FVEP example 1. The patient was 6 years old, and the FVEP results showed that the amplitude of the P2 wave was greater than 20 μV, and the peak time was 95–110  ms, both of which were within the normal range of children’s FVEP, with good repeatability and reliable results. FVEP normal reference values: In general, P2 amplitude in children under 15 years is >20 μV,

P2 amplitude in the adult is 7–20 μV, and the P2 peak time is about 95–110  ms. FVEP variation is larger, and it should be analyzed combined with binocular values, when the difference between binoculars >30%, the eye with worse results should be abnormal, even if binocular values are in the normal range

3.2.6.4 Abnormal FVEP Similar to PVEP, the anomaly of FVEP mainly includes the anomaly of amplitude and peak time, as shown in Fig. 3.12.

3.3

 ERG Basic Features ff and Report Reading Key Points

3.3.1 ff  ERG Basic Process and Signal Origin ffERG is the sum of the electrical responses of neurons and non-neuron cells in the retina recorded from the electrode of the cornea when the retina is stimulated by a full-field (Ganzfeld) flash, and it represents the total electrical activity

of cells in all layers of the retina, from photoreceptors to bipolar cells and amacrine cells. ffERG is also affected by lesions in the pigment epithelium on the outside of the receptor cells. The corresponding relationship between waveform components of visual electrophysiological examination and retinal hierarchy is shown in Fig. 3.13. Figure 3.14 represents the local electrical conduction pathway of the retina. The potential difference of ffERG recorded on the corneal electrode can be represented by B in the figure. ffERG potential from the retina through the vitreous and cornea, and then through the choroid and RPE back to the retina. So, the signal that ffERG records are the potential difference in the retina [3]. When the rhodopsin in the outer part of the photoreceptor absorbs light, it triggers a series of molecular activities that eventually lead to the hyperpolarization of the photoreceptor. The

3.3  ffERG Basic Features and Report Reading Key Points

23

Fig. 3.11  Normal FVEP example 2. The subject was 22 years old. The twice repeated examinations of FVEP P2 in both eyes

showed consistent waveform, and normal amplitude and peak time and good consistency indicate reliable results

Fig. 3.12  Example of abnormal FVEP (abnormal double eyes). Patient at the age of 37 years, FVEP showed that P2 wave amplitude was significantly lower than normal for

the same age group, with normal peak time. Twice repetitions of both eyes showed good consistency of P2 waves, suggesting reliable results

sum of these potential changes is the negative a-wave recorded on the corneal electrode. A wave of dark adaptation ERG mainly reflects

the activity of rod cells, while a wave of light adaptation ERG mainly reflects the activity of cone cells. The hyperpolarization of photore-

24

3  Visual Electrophysiology Result Reading Key Points

Fig. 3.13  Retinal structures corresponding to various types of visual electrophysiological waveforms

ceptors reduces the release of neurotransmitters at the end of the synapse that regulates postsynaptic bipolar and horizontal cells, respectively. The extracellular K+ concentration was increased by the depolarization of ON bipolar cells, and this potential change occurred in the outer plexus layer, which further guided the depolarization of Müller cells. The resulting cross-retinal current flows along the Müller cells to form the ERG’s b wave. At the same time, extracellular K+ concentration on the inner plexus layer was also increased, which may be caused by the depolarization of amacrine cells, bipolar cells, and ganglion cells.

3.3.2 ff  ERG Active Electrode Selection ffERG generally uses ERG-jet electrode with high recording amplitude, which is most widely used in clinical practice. Figure 3.15 is the schematic diagram of ERG-jet electrode installation. ffERG recording can also be performed with DTL electrodes, which have the advantage of low noise and good tolerance when recording for a long time. The electrode pair is placed in the lower conjunctival sac. Figure  3.16 is the schematic diagram of DTL electrode installation. HK-Loop electrode can

3.3  ffERG Basic Features and Report Reading Key Points

25

Fig. 3.17 Schematic diagram of HK-loop electrode installation

Fig. 3.14 Schematic diagram of ffERG recording principle

Fig. 3.18  Schematic diagram of Gold foil electrode installation

Fig. 3.15 Schematic diagram of ERG-jet electrode installation

be also used for ffERG active electrode, its amplitude is about two-third of that of ERG-jet electrode, it can be sterilized by gas or autoclaving, and it is comfortable to the patients. Figure  3.17 is the schematic diagram of HK-Loop electrode installation. Gold foil electrode is applicable for ffERG active electrode, and with about two-third amplitude of one of ERG-jet electrode, and comfortable for patients. Figure 3.18 is the schematic diagram of Gold foil electrode installation.

3.3.3 ffERG Basic Waveform

Fig. 3.16  Schematic diagram of DTL electrode installation

The ffERG basic waveform consists of a downward negative wave and a fast upward positive wave. See as Fig. 3.19.

26

3  Visual Electrophysiology Result Reading Key Points

Figure 3.20 shows three abnormal waveforms on the right, of which the upper right of the figure shows a slight decrease in the amplitude of the b wave. The middle figure on the right shows a serious decrease in the amplitude of the b wave. The lower figure on the right shows the unelicited waveform.

Fig. 3.19  Schematic diagram of ERG basic waveform

3.3.4 ff  ERG New International Standard Changes ffERG is the first inspection item of the international standard formulated by ISCEV, which initially includes five inspection items, namely the five items of the international standard (rod response, scotopic maximal response, oscillatory potentials, single-flash cone response, and 30-Hz flicker response) [4]. In 2008, an optional item (10 or 30 cd s/m2 high flash stimulation response for preoperative examination of patients with refractive media opacity) was added, i.e., six international standards [5]. In 2015, ISCEV renamed 6 ERGs (Table  3.3) according to the principle of light intensity of stimulus and dark adaptation or light adaptation [1]. The 2015 ISCEV international standard stipulates that ffERG measurement includes the amplitude and peak time of each wave, and clearly defines the concept of peak time, also known as implicit time, which refers to the time from stimulus starting to b wave peak or a wave trough. The amplitude of a wave is from the baseline to the bottom of a wave, while the amplitude of b wave is from the bottom of a wave to the top of b wave (see Fig. 3.1) [1].

3.3.5 ff  ERG Normal and Abnormal Waveform Contrast 3.3.5.1 Dark-Adapted 0.01 ERG Normal Versus Abnormal Waveforms Dark-adapted 0.01 ERG normal typical waveform is a wave without negative direction, only positive b wave at about 90 ms, and the b wave amplitude is normally greater than 200 μV, see Fig. 3.20, left.

3.3.5.2 Dark-Adapted 3.0 ERG Normal and Abnormal Waveform Contrast Figure 3.21 shows the comparison of dark-­ adapted 3.0 ERG normal and abnormal waveforms. The upper left figure is a typical normal wave, that a wave amplitude greater than 200 μV, b wave amplitude greater than 400  μV, and b/a ratio greater than 1.5. The other four images showed abnormal waveforms. The down left figure showed the decreased amplitude of both a wave and b wave, which were seen in a large range of retinopathy. The upper right figure shows a wave amplitude decreased, b wave amplitude is normal, which is seen in myopic patients. The middle figure on the right shows that a wave amplitude is normal, b wave amplitude decreases, b wave amplitude is lower than a wave, that is, b/a 200  μV; Dark-­ adapted 3.0 ERG a wave amplitude is generally >200 μV, b wave amplitude is generally >400 μV. The waveforms of dark-adapted 10.0 ERG and dark-adapted 3.0 ERG in nor-

31

mal people are similar, and the amplitudes of their a and b waves are also basically the same. Generally, dark-adapted 3.0 oscillation potential P2 wave amplitude (OS2) >60 μV. Light-adapted 3.0 ERG b wave amplitude is general >100  μV, light-adapted 30  Hz Flicker response P2 wave amplitude (a2–b2) is general >70 μV (In this figure, Normals is the recommended reference value of Roland Consult electrophysiology, and there are some differences among different brands)

32

Fig. 3.25 (continued)

3  Visual Electrophysiology Result Reading Key Points

3.3  ffERG Basic Features and Report Reading Key Points

33

3.3.9 E  xamples of Abnormal ffERG Clinical Report and Key Points of Reading the Diagram Figures 3.26 and 3.27 are examples of abnormal ffERG.

Fig. 3.26  Abnormal ffERG example 1 (abnormal right eye). The patient, 53 years old, had basically normal 6 ffERG responses in the left eye and moderately decreased amplitude of each wave in 6 ffERG responses in the right eye

34

Fig. 3.26 (continued)

3  Visual Electrophysiology Result Reading Key Points

3.3  ffERG Basic Features and Report Reading Key Points

35

Fig. 3.27  Abnormal ffERG example 2 (binocular abnormality). The 57-year-old patient showed a moderate decrease in bilateral ffERG 6 responses amplitude

3  Visual Electrophysiology Result Reading Key Points

36

Fig. 3.27 (continued)

3.4

 ERG Basic Features P and Report Reading Key Points

3.4.1 P  ERG Basic Process and Its Clinical Significance

PERG is the electrical response produced by alternate pattern retinal stimulation (reverse black and white checkerboard, in 2013 ISCEV standards it is 48′, 0.8° spatial frequency, 4 rps, 100–300 average times, stimulating pattern as shown in Fig. 3.28) [6], it not only can evaluate macular function, but also can evaluate the func-

3.4  PERG Basic Features and Report Reading Key Points

37

Fig. 3.30  Schematic diagram of amplitude reduction of PERG P50. The abnormal (dotted line) P50 amplitude in the figure is lower than the normal (solid line) P50 amplitude, accompanied by a decrease in N95 amplitude

Fig. 3.28  PERG 48′ checkerboard stimulation pattern diagram

Fig. 3.31  Schematic diagram of decreased amplitude of PERG N95. In the figure, the abnormal (dotted line) N95 amplitude is lower than the normal (solid line) N95 amplitude, while the dotted line P50 amplitude is still normal

Fig. 3.29 Schematic waveform

diagram

of

PERG

normal

tion of the inner retinal ganglion cells, and furtherly interpret the PVEP reaction induced by the same stimulus.

3.4.2 PERG Waveform The normal waveforms of PERG are upward P50 wave and downward N95 wave. Normal waveform characteristics: P50 peak time is about 50 ms, amplitude is about 3 μV; The peak time of P95 is about 95–100  ms, and the amplitude is about 5 μV (Fig. 3.29). N95 mainly originates from ganglion cells, so that N95 amplitude is mainly affected by optic neuropathy, and P50 may originate from the far-

ther retina. The dotted lines in Figs. 3.30 and 3.31 show the waveforms of P50 reduction and N95 reduction, respectively.

3.4.3 PERG Scope of Application The clinical application scope of PERG is as follows.

3.4.3.1 Macular Disease PERG can be used to evaluate the function of macular disease and monitor the disease status. 3.4.3.2 Hereditary Retinopathy and Retinal Vascular Diseases PERG can be used for the comprehensive assessment of hereditary retinopathy and retinal vascular diseases.

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3  Visual Electrophysiology Result Reading Key Points

3.4.3.3 Optic Nerve Disease (e.g., Glaucoma) PERG can be used for early screening, diagnosis, and monitoring of glaucoma patients.

3.4.5 E  xamples of Abnormal PERG Clinical Report and Key Points of Reading the Diagram

3.4.3.4 Lesion Localization PERG combined with PVEP could localize the lesion.

Figures 3.33 and 3.34 are examples of abnormal waveforms of PERG.

3.5

 fERG Basic Features m and Report Reading Key Points

3.4.4 E  xamples of Normal PERG Clinical Reports and Key Points of Reports Reading

3.5.1 mfERG Basic Concept

PERG waveform variation is small, but due to low amplitude, easy to be affected by noise. Clinical PERG examination needs to be repeated at least twice, good repeatability is high reliability. Figure 3.32 is an example of a normal clinical report of PERG.

mfERG was invented by Sutter in 1992. Recording electrode is still the cornea contact lens electrode, DTL electrode, HK loop e­ lectrode, or Gold Foil electrode, stimulating graph is some black and white hexagons (usually 61 or 103) (Fig. 3.35), at one time, half of all the stimulus

Fig. 3.32  Example of normal PERG. The subject, 59 years old, had a normal amplitude of PERG P50 and N95 in both eyes, and good repeatability. Normal PERG P50 amplitude >3 μV, N95 amplitude >5 μV

3.5  mfERG Basic Features and Report Reading Key Points

39

Fig. 3.33  Abnormal PERG example 1 (binocular abnormality). The 35-year-old patient had a moderate decreased amplitude of P50 and N95 in the left eye of PERG, and no significant PERG waveform was observed in the right eye

hexagons are black and others are white, black and white hexagons are converted, the retina ERG waveform curve of the corresponding area can be recorded through computer processing. That is the multifocal ERG. Traditional electrophysiology uses the full-­ field Ganzfeld stimulator to stimulate the whole retina with flashing light, which reflects the comprehensive characteristics of electrical signals of the whole retina. However, the specific lesion site cannot be determined. Multifocal electrophysiology uses CRT, LED, LCD, or SLO stimulator to stimulate the retina graphically, which reflects the signal characteristics of each tiny part of the retina. The specific retinal region of the lesion can be determined, which is  equivalent to the ­collection of traditional focal electrophysiological signals in different regions [7].

The centrifugal distribution of the hexagon makes the amplitude density of the signal derived from the hexagon in the central region slightly different from that in the peripheral region, which can be presented in one picture. The larger area of the peripheral hexagon corresponds to the lower density of the cone cells in the peripheral area and increases with centrifugal distance, so small peripheral responses can be recorded. Each hexagon controls the black-and-white flip of the stimulus pattern in a pseudo-random order of m sequences. The local reaction was obtained using a cross correlation between m sequence and reaction period. The amplitude density of retinal responses (amplitude per degree square of the retina) obtained from different hexagonal regions (Fig. 3.36) is shown in a combination

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3  Visual Electrophysiology Result Reading Key Points

Fig. 3.34  Abnormal PERG example 2 (abnormal right eye). The patient, 51 years old, had a normal peak time and amplitude of P50  in the right PERG

eye, a moderate decrease in the amplitude of N95, and a normal amplitude of PERG P50 and N95 in the left eye

Fig. 3.35  mfERG stimulus figure 61 and 103 hexagons

3.5  mfERG Basic Features and Report Reading Key Points

Fig. 3.36  mfERG 61 original hexagon waveforms and amplitude density. The original waveform is composed of 61 individual waveforms, each of which is composed of

41

negative N1 and positive P1 waves. The amplitude of P1 wave is generally observed

result of the corresponding color and height to obtain an electroretinogram 3D topographic map (Fig. 3.37).

3.5.2 Three ERGs Comparisons ffERG, PERG, and mfERG have different stimulation scope, stimulation mode and clinical significance, and cannot replace each other. Table  3.4 shows the comparison of the three ERGs.

3.5.3 Scope of Application for mfERG Fig. 3.37  mfERG 61 hexagonal 3D topographic maps

The clinical application of mfERG is as follows.

Origin of waveform

Evaluation index

Normal typical waves

Indicators

Most of them are a wave amplitudes and b wave amplitudes a wave originates from rods or cones, while b wave originates from bipolar cells

ffERG waves normal typical waveform diagram

Schematic diagram of total retinal stimulation range

ffERG

Table 3.4  Comparison of ffERG, PERG, and mfERG

The receptor cells and the adjacent retinal cells drive P50 wave, and the N95 wave comes from the ganglion cell response

P50 N95 wave amplitudes

PERG normal typical waveform diagram

Schematic diagram of the stimulation range of macular and peripheral diameter 17°

PERG

The N1 wave is same as light-adapted 3.0 ERG a wave and originated from the cones. The components of P1 waves are same as light-adapted 3.0 ERG b waves, originating in bipolar cells. N1 wave is originated from nerve ganglion cell

mfERG 61 original hexagonal waveforms and amplitude density 61 or 103 P1 wave amplitudes density

Schematic diagram of the stimulation range of macular and posterior pole diameter 60°

mfERG

42 3  Visual Electrophysiology Result Reading Key Points

Disease to be used

Clinical significance

The average numbers

Waveform characteristics

Retinopathy

The 6 different responses have different waveform characteristics, with a high amplitude up to 100–600 μV, which is easy to collect, and does not need to collect multiple times to average, with small variation among different patients Can stimulate 1–3 times according to the waveform Reflects the overall function of the retina, including both cone and rod cell functions

Macular degeneration, optic neuropathy

Can stimulate 100–300 times according to the waveform P50 reflects macular function, and N95 reflects ganglion cell function

Amplitude is low, only about 3 μV, susceptibly to the interference noise

Can stimulate 4–8 cycles according to the waveform P1 wave reflects the function of retinal cone cells and bipolar cells in each corresponding hexagonal region of macula and posterior pole Macular lesion, posterior pole fundus lesion

Not the amplitude, but the amplitude density, which has been averaged with the corresponding area, unit nV/deg2, is highly susceptible to interference; High amplitude shows good function

3.5  mfERG Basic Features and Report Reading Key Points 43

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3  Visual Electrophysiology Result Reading Key Points

3.5.3.1 Quantitative Evaluation of the Therapeutic Effect of Fundus Diseases mfERG can be used for quantitative evaluation of the efficacy before and after fundus surgery, drug, and laser treatment.

amplitude density, and waveform parameters can be modified to peak time and other indicators when there is special demand. In the upper-middle 2D image, the amplitude density of each original waveform P1 wave is shown in different colors, and interpolation is inserted, which is used to describe the scope and orientation of the overall lesion, similar to the grayscale map of the static perimetry. On the right scale, warm colors represent higher amplitude density, while cool colors represent lower amplitude density. Local dark blue areas can be seen in the middle area of the nasal side in the above figure, corresponding to the original waveform, corresponding areas can also be seen, corresponding position waveform has not been extracted, indicating that this position is optic disc, that is, the physiological blind spot area. If the physiological blind spot is visible in the examination result, the patient’s fixation is good and the result is reliable. The 3D diagram on the top right shows the amplitude density of each region with height and color, and also has interpolation, which can directly reflect the functions of macular fovea and its surrounding regions. In the 3D chart, relative to internal normal should be observed, that is, the maximum value of scale should be set as the upper limit of normal value to reflect the abnormal situation more intuitively. If 2D and 3D results were compared with the results of fundus image or static perimetry examination, it should be paid attention to the direction of the field of view, which can be divided into retinal view and static perimetry view. Relevant information can be seen at the bottom right of mfERG patient information bar. In this case, it is retina view, the mfERG result is consistent with the direction of the fundus photograph. If necessary, the parameters can be modified to be consistent with the static perimetry view. The lower left ring diagram can describe the amplitude density anomaly of fovea, paracentric fovea and peripheral macular area, and can be used to observe the progress of fundus lesions with the macular center as the initial lesion site. The normal amplitude density range of 1–5 rings (the default normal value range in the print result is for reference only, which can be modified according to the statistical results of the normal

3.5.3.2 Hereditary Retinopathy mfERG can help in the diagnosis, functional assessment, and overall monitoring of hereditary retinopathy such as retinitis pigmentosa. 3.5.3.3 Macular Degeneration mfERG can be used to evaluate the function of macular degeneration such as Stargardt disease. 3.5.3.4 Retinal Vasculopathy mfERG can be used to evaluate and guide the treatment of diabetic retinopathy and other retinal vascular diseases. 3.5.3.5 Retinal Toxicity Drug Monitoring mfERG can be used to detect and guide the treatment of retinopathy caused by chloroquine. 3.5.3.6 Preoperative Assessment of Retinal Function for Cataract If the central peak of mfERG is significantly higher than that of the surrounding retina, even if it is lower than normal, retinal function is not that poor.

3.5.4 E  xamples of Normal mfERG Clinical Reports and Key Points of Reading Figure 3.38 shows an example of 61 hexagon normal waveforms in mfERG. The original waveform on the top left image is each hexagon’s original waveform. In general, the positive wave is the amplitude density of P1 wave, and the negative wave is the amplitude density of N1 wave. The general situation of the whole stimulus field of vision can be observed through the waveform. The obvious positive and negative waves indicate that there is little interference, and low amplitude density of positive wave indicates poor function of this region. Usually, waveform parameters are set as P1

Fig. 3.38  Example of 61 hexagon mfERG normal waveforms. The subject was 46 years old. In this result, the original waveform figure and 3D figure were mainly analyzed. In the quantitative description of the result, the abnormal degree of the

amplitude density and the corresponding peak time were respectively described for 5 or 6 rings curves(6 rings in 103 hexagons stimuli result and 5 rings in 61 hexagons stimuli) and four quadrantals curves

3.5  mfERG Basic Features and Report Reading Key Points 45

46

3  Visual Electrophysiology Result Reading Key Points

value of your examination room) is roughly >100  nV/deg2, >60  nV/deg2, >40  nV/deg2, >30 nV/deg2, and >20 nV/deg2. The lower middle quadrant diagram can describe the amplitude density anomalies of the four quadrants of the superior nasal, inferior nasal, superior temporal, and inferior temporal, and it is used to observe the progress of fundus lesions with the non-macular center as the initial lesion site. The normal amplitude density of the four quadrants is about >30  nV/deg2, among which the amplitude density of the superior nasal and inferior nasal quadrants was slightly lower due to optic disc. Figure 3.39 shows an example of 103 hexagon normal waveforms in mfERG.

(Fig.  3.43). Arden ratio is the main evaluation index. In 2017, ISCEV changed the name of Arden ratio to Light Peak: Dark Trough ratio (LP: DT ratio) [8].

3.6.2 Application Scope of EOG 3.6.2.1 Best Disease (Vitelliform Macular Dystrophy) EOG of Best disease has specific LP: DT radio reduction, which is one of the diagnostic basis. 3.6.2.2 Pigment Epithelial Lesion EOG can be used in the diagnosis, genotyping, and disease monitoring of pigment epithelial lesions.

3.5.5 E  xamples of Clinical Reports of mfERG Abnormalities and Key Points of Image Reading

3.6.2.3 Choroid Lesions EOG can be used to locate choroid lesions, and abnormal EOG is often seen in choroid tumors.

Figures 3.40, 3.41, and 3.42 are examples of mfERG abnormal waveform.

3.6.3 E  xamples of Normal EOG Clinical Reports and Key Points of Reading

3.6

EOG should detect the light peak and dark valley amplitude ratio (normal value: 1.8–4.3). We also need to observe dark valley potential and light peak potential amplitude and peak time. Peak of light peak potential is normally at 5–12  min. Figure 3.44 shows an example of a normal EOG waveform.

 OG Basic Features E and Report Reading Key Points

3.6.1 E  OG Recording Process and New Changes in International Standards EOG measures the retinal static potential between retinal pigment epithelium and photoreceptor cells. Electrodes were placed in the inner and outer canthus of the subject, and the changes in the current generated by the rotation of the eyeball could be detected under dark and bright conditions. The recorded potential is EOG

3.6.4 E  xamples of Abnormal EOG Clinical Reports and Key Points of Reading Figure 3.45 shows an example of EOG abnormal waveform

Fig. 3.39  103 hexagon mfERG normal waveforms. Subject, 19 years old, this sample was normal 103 hexagon mfERG results. The original waveform, 2D and 3D images showed clear dark blue optic disc area in the middle area of the nasal side, with good fixation. There were six rings in the ring diagram, and the normal

ranges of each ring were slightly lower than the amplitude density of the 61 hexagons, respectively >90 nV/deg2, >50 nV/deg2, >30 nV/deg2, >20 nV/deg2, >15 nV/ deg2, >10 nV/deg2. The amplitude densities of the four quadrants in the quadrant diagram are roughly >20 nV/deg2

3.6  EOG Basic Features and Report Reading Key Points 47

Fig. 3.40  Abnormal mfERG example 1. The patient was 63-years old. The amplitude density of ring 1 in the center of the rings graph of the case was moderately decreased, and those of ring 2–5 were slightly decreased. The peak of the 3D graph was basically disappeared

48 3  Visual Electrophysiology Result Reading Key Points

Fig. 3.41  Abnormal mfERG example 2. The patient was 72 years old. The amplitude densities of each ring in the center of mfERG’s macular area were severely decreased, and the 3D peak disappeared

3.6  EOG Basic Features and Report Reading Key Points 49

Fig. 3.42  Abnormal mfERG example 3. The patient was 37 years old. The peak of the mfERG 3D map was normal, the amplitude density of the first ring in the center of the ring map was normal, the amplitude densities of the superior temporal and

inferior temporal quadrants were moderately decreased, and the amplitude densities of the two nasal quadrants were slightly decreased

50 3  Visual Electrophysiology Result Reading Key Points

3.6  EOG Basic Features and Report Reading Key Points

51

Fig. 3.43  EOG typical normal waveform

Fig. 3.44  Example of normal EOG. The examinant was 33 years old. The marked positions of the troughs and peaks of both eyes in this example correspond to the marked positions of troughs and peaks, and the marks were correct. Arden ratio (the new international standard

name is LT:DT ratio, namely light peak and dark valley amplitude ratio) is >1.8, in the normal range. Dark valley peak time >6′, and light peak time >7′, and they both are in normal time range (general peak times of dark trough and light peak are >5′)

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3  Visual Electrophysiology Result Reading Key Points

Fig. 3.45  Abnormal EOG example (binocular anomaly). The patient was 28 years old. Both the dark adaptation trough and the light adaptation peak were obvious, and the difference between the two was small. The ratio of light peak and dark valley was less than 1.8, indicating a mod-

erate abnormal result (the ratio of light peak and dark valley was slightly decreased from 1.5 to 1.8, moderately decreased from 1.2 to 1.5, and severely decreased from 1.2)

4

Visual Electrophysiology Clinical Cases

4.1

Visual Electrophysiology Examination Selections and Application Scope

4.1.1 Visual Electrophysiology Examination Selections Protocol The results of visual electrophysiology are objective and reliable, and they can also be quantitatively analyzed. Now, it has become a necessary means for the diagnosis of complex fundus disease and optic nerve disease, especially for some patients complaining of decreased vision, but other eye examinations did not find abnormal, visual electrophysiological examination has its unique advantages. According to the visual electrophysiological examination process shown in Fig. 4.1, fundus lesions can be checked step by step, and then the lesion location and disease character can be speculated. As shown in Fig. 4.1, when patients with clinical complaints of unclear visual objects and no abnormalities in the morphology of the fundus are encountered, PVEP examination should be performed first. Then visual electrophysiological examination items required for the next step should be selected according to different results of PVEP. 1. When PVEP shows decreased amplitude or delayed peak time, optic nerve or macular degeneration shall be considered. At this

point, PERG or mfERG should be performed to confirm the diagnosis further. If the amplitude of P50 decreased in PERG results or the amplitude density of mfERG fovea decreased, macular degeneration was considered. If P50 amplitude is normal, N95 amplitude decreased, and mfERG is normal, optic neuropathy should be considered. 2. Check FVEP when no waveform is extracted from PVEP.  As with FVEP, no waveforms were induced and optic neuropathy was considered. If the FVEP amplitude decreases or the peak time is delayed, further ffERG examination is required. Peripheral retinopathy was considered if ffERG results showed the decreased amplitude of dark adaptation and light adaptation. If ffERG is normal, the main consideration is optic neuropathy. 3. PVEP was normal, ffERG or mfERG were checked again. If there is amplitude or amplitude density decrease, consider retinopathy; If both are normal, consider hysteria.

4.1.2 A  pplication Scope of Visual Electrophysiology For different lesions, the purpose of electrophysiological examination is different, and the clinical guidance is also different. In clinic, the main application value of the visual electrophysiology mainly lies in diagnosis, differential diagnosis,

© People’s Medical Publishing House, PR of China 2022 R. Sui et al., Practical Visual Electrophysiological Examination, https://doi.org/10.1007/978-981-16-8910-9_4

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4  Visual Electrophysiology Clinical Cases

54

Fig. 4.1  Flow chart of visual electrophysiological diagnosis of complex fundus lesions and optic nerve diseases

function evaluation, follow-up, etc. of optic neuropathy, retinopathy for infants, hereditary retinopathy including occult retinopathy, acquired retinopathy, retinal toxic lesions, glaucoma and amblyopia and other eye diseases, refractive medial opacity preoperative retina function assessment, ocular trauma, and eye diseases judicial authentication.

4.2

Optic Neuropathy

Optic neuropathy is a common cause of visual acuity decline in ophthalmology, and the possibility of optic neuropathy should be considered for visual acuity decline of unknown cause in clinic. For suspicious optic neuropathy, PVEP, FVEP, and PERG should be selected, which can be used for qualitative diagnosis of optic nerve conduction abnormal or degeneration-like lesions of optic nerve according to VEP.  Conversely, these tests can also differentiate the disease and exclude optic neuropathy.

4.2.1 Optic Nerve Demyelination Optic nerve demyelination includes optic neuritis, multiple sclerosis, and optic neuromyelitis. Its VEP mainly consists of peak-time delay. VEP can reflect the optic nervous system lesions of any part from retinal ganglion cells to the visual cortex, so PVEP and FVEP are the preferred visual electrophysiological examinations for optic nerve dis-

eases. PERG N95 can reflect the function of ganglion cells and can help to locate optic neuritis. For optic neuritis, especially for some intrabulbar optic neuritis without changes in the fundus, visual electrophysiological examination can provide an objective evaluation of optic nerve function for patients, which has a high diagnostic value. Figure 4.2 shows PVEP results of patients with optic neuritis. PVEP showed a peak time delay, and it still showed a peak time delay during the convalescence period, often accompanied by the peak time delay of the contralateral eye (>10 ms). Due to the simultaneous damage of retinal ganglion cells, PERG can also show an abnormal amplitude of N95. Some patients can be seen decreased amplitude and shortened peak time of P50, but P50 delay is not a characteristic change of optic nerve disease and ganglion cell lesion [9].

4.2.2 Degeneration of the Optic Nerve Degenerative diseases of the optic nerve include optic atrophy, ischemic optic neuropathy, and Leber hereditary optic neuropathy. The visual electrophysiological changes of these diseases are mainly decreased VEP amplitude. The following case is nonarteritic anterior ischemic optic neuropathy (NAION), a type of ischemic optic neuropathy. The electrophysiological changes are mainly PVEP (Fig. 4.3) and FVEP amplitudes are reduced, and a few patients have peak time delay [9].

4.3 ROP

55

Fig. 4.2  Optic neuritis PVEP. The patient, 65 years old, had delayed peak times of 1° and 15′ P100 in both eyes and normal amplitudes except the significantly lower amplitude of 15′ PVEP in the right eye than that in the left eye

4.3

ROP

Because retinopathy of premature babies cannot cooperate with visual acuity, and visual electrophysiological examination must be under ­anesthesia

for visual function assessment. The visual electrophysiological examination has important value for retinopathy of premature babies, and ffERG and FVEP examination can accurately assess retinal function and visual pathways function in infants.

4  Visual Electrophysiology Clinical Cases

56

Fig. 4.3  Anterior ischemic optic neuropathy PVEP. The patient was 64 years old. PVEP, in this case, showed a moderate decrease of 1°P100 amplitude in the left eye

Children with retinopathy of prematurity may undergo an ffERG test under general anesthesia or with a sedative to be known the function of the retina before and after treatment. Figure  4.4 shows ffERG results of a 1 year and 10 months old infant with retinopathy of prematurity.

4.4

Inherited Retinopathy

ffERG, PERG, EOG, and mfERG should be examined for genotype and disease prediction of hereditary retinopathy. For hereditary retinopathy, it is possible that there is a mismatch between fundus morphology and electrophysiological function findings. As some patients with inner retina lesions, fundus may be normal sometimes, and visual electrophysiological examination dysfunction can often appear before morphology changes, so visual electrophysiological examination is helpful to diagnosis of inherited retinopathy or classification of diseases. Genetic classification can help children to predict disease outcomes. Of course, the final diagnosis of genotype needs to be determined by genetic diagnosis. Figure 4.5 shows the classification of hereditary retinopathy [10].

compared with that in the right eye, and P100 peak was normal in both eyes

4.4.1 Stargardt’s Disease Stargardt’s disease, also known as fundus flavimaculatus, is an autosomal recessive disease of binocular symmetry. Most of the patients developed the disease in the adolescent period, with rapid loss of central vision. Most Stargardt’s disease is related to the mutation of ABCA4 gene in chromosome 1p21–p13, and the fundus can show yellow spots in macular area and macular atrophy. The visual electrophysiological abnormalities in this disease mainly showed the decreased amplitude of P50 and N95  in PERG (Fig.  4.6), decreased amplitude density in the central macular area in mfERG (Fig. 4.7), while ffERG was normal [10].

4.4.2 Bull’s Eye Maculopathy Bull’s eye maculopathy is usually referred to as cone dystrophy, but includes cone-rod dystrophy and rod-cone dystrophy. ffERG and PERG should be observed for bull’s eye maculopathy patients. ffERG is the diagnosis basis for cone dystrophy. The patients mainly have the decreased

4.4  Inherited Retinopathy

57

Fig. 4.4  Retinopathy of prematurity ffERG. The patient was 1 year and 10 months old. No waveform was generated in the case of binocular all dark adaptation and light adaptation responses

58

4  Visual Electrophysiology Clinical Cases

Fig. 4.4 (continued)

amplitudes of the two responses of light adaptation and the normal amplitudes of the four responses of dark adaptation. Abnormal ffERGs of cone-rod cell dystrophy and rod-cone dystrophy are, respectively, given mainly to with lightadapted and dark-adapted responses amplitudes decrease. Fundus autofluorescence of RPE (retinal pigment epithelium) shows a pale ring. Figure 4.8 shows ffERG results of cone dystrophy [10].

4.4.3 Best Vitelliform Macular Dystrophy Best vitelliform macular dystrophy (BVMD) is also known as Best disease. This disease is autosomal dominant and occurs in adolescents. When the VMD2 gene located in chromosome 11q13 is mutated, its encoded protein bestrophin-1 appears abnormal function, causing this disease. Yellow

4.4  Inherited Retinopathy

59

Fig. 4.5  Classification of hereditary retinopathy

yolk-like macular lesions are seen in the early stage of the disease, which is associated with lipofuscin accumulation at the level of RPE. Early vision is not affected. Visual electrophysiology usually shows ffERG normal, EOG light peak decreased, LP/DT (light peak and dark trough ratio) less than 1.5. Figure 4.9 shows the EOG results of a case of Best disease. The light peak and dark trough ratio of EOG in both eyes is 1.2, and the light peak and dark trough waves are not obvious [10].

4.4.4 C  ongenital Stationary Night Blindness Congenital stationary night blindness (CSNB) is manifested as night blindness at birth, loss of central vision, nystagmus and strabismus, and often accompanied by myopia, so the fundus can be normal or myopic fundus. The visual electrophysiology of CSBN is negative wave ERG. According to the visual electrophysiological manifestations, CSBN can be divided into complete and incomplete types. Complete CSNB dark-adapted response cannot be detected by 0.01 ERG response. The ampli-

tude of a wave is normal, while the amplitude of b wave is negative. The light adapted 3.0 ERG and 30  Hz flicker light responses are basically normal or slightly abnormal (Fig.  4.10). Incomplete CSNB can be detected in the dark adapted 0.01 ERG response, but it is lower than normal. The dark adapted 3.0 ERG is significantly abnormal with negative wave type, while the light adapted 3.0 ERG response and 30  Hz flicker light response are basically normal or slightly abnormal (Fig. 4.11) [10].

4.4.5 X-Linked Juvenile Retinoschisis The onset of X-linked juvenile retinoschisis (XLRS) is almost in preadolescence, with symptoms of impaired vision. Fundus abnormalities can be observed in most patients, with early ophthalmological examination showing that the characteristic spoke-like manifestations of m ­ acular fovea, nonspecific macular atrophy in the later stage, central retinal crystal-like changes in OCT, and peripheral retinoschisis lesions in 50% of the patients in the superior temporal fundus.

4  Visual Electrophysiology Clinical Cases

60

Right Eye

Left Eye

Fig. 4.6  Stargardt’s disease PERG. Binocular PERG waveforms were not induced in this case

Visual electrophysiological examination can provide the basis for some X-linked juvenile retinoschisis to confirm diagnosis, such as the nonspecific macular atrophy cases without peripheral retinoschisis, ffERG dark adaptation in 0.01 ERG is usually undetectable or significantly reduced, dark adapted 3.0 ERG response abnormal, a typical negative wave type, and light adapted 3.0 ERG and 30 Hz flicker ERG amplitudes decrease or peak time is delayed (Fig. 4.12) [10].

4.4.6 Retinitis Pigmentosa Retinitis pigmentosa (RP) is characterized by sex-linked recessive inheritance, autosomal

recessive inheritance, autosomal dominant inheritance, double-gene inheritance, mitochondrial inheritance, etc. Almost 1/3 RP cannot be determined from family history. Early fundus can be normal, with the development of the disease fundus can be seen with extensive retinal pigmentation. Typical symptoms include night blindness and decreased field of vision, and central vision may remain or change slowly than peripheral vision. The changes of visual electrophysiology are progressive receptor dysfunction, among which the damage of rod cells is greater. The visual electrophysiology of retinitis pigmentosa shows ffERG dark adapted 0.01 response b wave amplitude decreases. The amplitudes of a wave and b

Fig. 4.7  Stargardt’s disease mfERG. The original mfERG waveform of this case showed that the waveform in the central area of the macula was not obvious, there was no warm color area in the center of the 2D diagram, and the central peak of the

3D diagram disappeared, the amplitude density of all the five ring regions decreased significantly in the rings diagram, and the amplitude density in the four quadrants decreased significantly in the quadrant diagram

4.4  Inherited Retinopathy 61

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4  Visual Electrophysiology Clinical Cases

Fig. 4.8  Cone dystrophy ffERG. In this case, the amplitudes of each wave of the four dark-adapted responses were moderately decreased, while the waveforms of the two light-adapted responses were not induced

4.4  Inherited Retinopathy

63

Fig. 4.8 (continued)

wave decrease in the dark adapted 3.0 response. The effect of light adapted 3.0 is not significant. Light adapted 30 Hz response peak time delays, the amplitude decreases, and the ffERG anomalies are more significant in the late stage of the disease. In the early stage of X-linked genetic RP (XLRP), ffERG amplitude severely decreases or cannot be detected, while autosomal dominant genetic RP (ADRP) progresses slowly.

Typical ffERG results are shown in Fig.  4.13. PERG and mfERG can be used to assess central retinal involvement in RP.  In some patients, ffERG cannot be detected (Fig. 4.14), but PERG P50 (Fig.  4.15) and mfERG central region (Fig. 4.16) may be normal. With the progress of the disease and macular involvement, both PERG and mfERG show severe reduction or no waveform [10].

4  Visual Electrophysiology Clinical Cases

64

Fig. 4.9  Best vitelliform macular dystrophy EOG. In this case, both the light peak and the dark trough waves were not obvious, and the difference between them was very

small. The ratio of light peak and dark trough was close to 1, which was a severe decrease

4.4.7 Occult Macular Dystrophy

4.5

Occult macular dystrophy (OMD) is characterized by low central vision and normal fundus morphology. The field of vision may have a central dark spot. OCT shows thinning of the macular area. The characteristic changes of visual electrophysiological examination are decreased amplitude densities of mfERG macular fovea and para-fovea (Fig. 4.17). ffERG and EOG are generally normal. 15′ PVEP amplitude can be reduced [10].

Acquired retinopathy refers to all non-hereditary fundus lesions, including acquired fundus lesions such as retinal vasculopathy, macular hole, and age-related macular degeneration. ffERG and mfERG examinations are required for quantitative functional evaluation and treatment guidance before and after treatment of the mentioned diseases.

Acquired Retinopathy

4.5  Acquired Retinopathy

Fig. 4.10  Complete CSNB ffERG. In this case, no waveform was generated by the dark adapted 0.01 ERG response. In the dark adapted 3.0 ERG response, the amplitude of a wave was normal, and that of b wave was

65

moderately decreased. b/a < 1, showing a negative wave type. The two light-adapted responses waveforms are normal

66

4  Visual Electrophysiology Clinical Cases

Fig. 4.10 (continued)

4.5.1 Diabetic Retinopathy In diabetic retinopathy (DR), microhemangioma, bleeding point, exudation, and cottonseed spot can be seen in the early stage of diabetic retinopathy, and microvascular changes, neo­ vascularization, and vitreous hemorrhage can be seen in the middle and late stages. The charac-

teristic electrophysiological changes are that ffERG dark adaptation responses b wave amplitudes and peak times are abnormal, and the degree of abnormality is related to the severity of the lesion. Abnormal oscillatory potential amplitude is one of the indications of severe NPDR and can guide treatment. ffERG waveform is shown in Fig. 4.18.

4.5  Acquired Retinopathy

Fig. 4.11  Incomplete CSNB ffERG.  In this case, the dark adapted 0.01 ERG response resulted in a severe decrease in b-wave amplitude, but the waveform was significant. The dark adapted 3.0 ERG response showed that a wave was basically normal, and b wave had a moderate

67

decrease in amplitude, b/a < 1, showing a negative wave type. The oscillatory potential response is not clear; the amplitudes of the two light-adapted responses were normal

68

Fig. 4.11 (continued)

4  Visual Electrophysiology Clinical Cases

4.5  Acquired Retinopathy

Fig. 4.12  X-linked juvenile retinoschisis ffERG.  The case ffERG dark adapted 0.01 response did not elicit waveform; dark adapted 3.0 response a wave amplitude was slightly reduced, dark adapted 3.0 b wave amplitude was severely reduced, and the b/a wave amplitude ratio was reduced, 400  V) or moderately decreased. However, arthritis, phenothiazines for psychosis, and ami- when the amplitude of dark adapted 10.0 ERG b nohexanoic acid for epilepsy. Additional copper, wave is more than 15% higher than that of dark lead, and iron also can cause retinal toxicity. adapted 3.0 ERG b wave, it indicates the normal ffERG and mfERG are commonly used tests for retinal function, and the amplitude of b wave was toxic retinopathy. decreased due to cataract. When the amplitudes The ffERG of hydroxychloroquine toxic reti- of dark adapted 3.0 ERG and dark adapted 10.0 nopathy shows the decreased amplitude of dark ERG are moderately and severely decreased, and adapted 3.0 ERG response b wave, showing a the amplitude of dark adapted 10.0 ERG b wave negative wave, and other waves can also be was increased less than 15% than that of dark abnormal as the disease progresses (Fig.  4.24). adapted 3.0 ERG b wave, the abnormal retinal mfERG also shows a decrease in the amplitude function is indicated, and the amplitude of b wave densities of the paracentric fovea (Fig.  4.25). was decreased due to retinopathy (Figs. 4.28 and EOG may have an exception. Visual electrophys- 4.29). iological changes may be earlier than fundus morphological changes.

4.8

4.7

Refractive Media Opacity

mfERG, ffERG, and FVEP can be used to evaluate the function of the retina before surgery and to predict the postoperative vision in patients

Glaucoma

Retinal ganglion cells are involved in early glaucoma, and morphological changes of ganglion cells in early glaucoma are difficult to detect. The retina’s response to the pattern, known as PERG, can assess early changes in ganglion cell func-

Fig. 4.23  Acute zonal occult outer retinopathy mfERG (right eye). Both the 2D and the 3D images of the case showed that the temporal region was deepened in cold tones, while the original waveform, 2D, 3D, and quadrant images showed that the amplitude densities of the temporal region were slightly decreased

86 4  Visual Electrophysiology Clinical Cases

4.8 Glaucoma

Fig. 4.24  Hydroxychloroquine toxic retinopathy ffERG.  In this case, the amplitude of dark adapted 0.01 ERG was significantly reduced, the a wave amplitude of dark adapted 3.0 ERG was slightly decreased; its b wave amplitude was severely decreased, b/a was 56  μV twice,

which was within the normal range (40–60  μV). The PhNR BT in the left eye was severely decreased twice

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4  Visual Electrophysiology Clinical Cases

Fig. 4.33  PVEP amblyopia. The binocular PVEP P100 amplitudes were severely reduced and the peak times were delayed

Fig. 4.34  Case 1 of forensic examination of visual function. The right eye PVEP 1° and 15′ waveforms were normal, and the visual acuity was above 0.3. The PVEP1° P100 amplitude of the left eye was normal, with a slight

delay in peak time, and 15′ P100 amplitude was moderately reduced, with a delay in peak time. The visual acuity was about 0.3

4.11  Eye Diseases Visual Electrophysiological Examinations Selection

Fig. 4.35  Case 2 of forensic examination of visual function. The patient’s left eye was normal at 1° and 15′ PVEP, with visual acuity above 0.3. Right eye 1°PVEP P100

97

amplitude severely decreased, 15′ P100 no waveform, visual acuity around 0.1

4  Visual Electrophysiology Clinical Cases

98 Fig. 4.36  Case 3 of forensic examination of visual function. (a) The objective visual acuity VEP SF limit examination result of the case was 1.18. Amplitude spatial frequency curve shows that with the increase of spatial frequency, amplitude is gradually reduced, but in lower 2 cpd spatial frequency, amplitude is not highest, and showed a trend of lower, the overall amplitude is from low to high, and then gradually reducing, it is the parabolic trend, it is the objective visual acuity spatial frequency amplitude curve normal performance. (b) The original waveform, the regularity of the steady-state response of sine wave. The last two curves have no obvious waveform, and they correspond to the last two red amplitudes in figure a, and they are close to the blue noise values

a

b

4.11  Eye Diseases Visual Electrophysiological Examinations Selection Fig. 4.37  Case 4 of forensic examination of visual function. (a) The objective visual acuity VEP SF limit of the case was 0.28, and only the first four amplitudes of the spatial frequency curves were above the noise value, showing typical parabolic trend. (b) Only the first four curves have waveforms, corresponding to the first four effective amplitudes in figure a, the last nine curves are basically interference waves, and the last nine amplitudes in figure a are basically noise ranges

a

b

99

Eye disease category/examination items Optic neuropathy Evaluation of visual function in infants Inherited retinopathy Acquired retinopathy Toxic retinopathy Refractive media opacity Glaucoma Amblyopia Eye diseases judicial expertise Differential diagnosis of retinal disease and optic nerve disease √ √ √

PVEP √

√ √ √

√

FVEP √ √

VEP SF limit

Special VEP

Table 4.1  Visual electrophysiological examination items corresponding to different eye diseases

√

√ √ √ √ √ PhNR ERG

ffERG

√

√

√

PERG √

√

√ √ √ √

mfERG

√

mfVEP

√

EOG

100 4  Visual Electrophysiology Clinical Cases

5

Visual Electrophysiology Equipment Install and Operation

5.1

Visual Electrophysiology Equipment Install

5.1.1 Installation of Ground Wires Since visual electrophysiology records weak bioelectric signals of microvolt (μV) level, in order to avoid the influence of various interference signals on the inspection results, the installation of ground wires should be standardized and independent. Installation of ground wire is also a necessary process to achieve leakage protection. The dedicated ground wire shall be connected to the ground wire connection port of the device’s main isolation power box (Fig. 5.1). The 2015 edition of the ISCEV ERG standard states that patients must be electrically isolated according to the safety current standard for clinical biometric recording systems in the user’s country. IEC60601-1 is the general standard for medical electrical appliances. The correct grounding method is to bury the grounding electrode: first, dig a hole with a depth of more than 2 m in the wet part of the ground, put a copper rod with a diameter of 1–2 cm and a length of 2–4 m, weld the wire, and then bury the wet soil to expose the wire to the ground. If the soil is dry, put salt and water around the

copper rod to reduce the grounding resistance (Fig. 5.2). Grounding resistance should be less than 4 Ω commonly. If the standard ground wire is installed unconditionally, the ground wire can be connected to the metal downpipe or heating pipe. Do not connect the ground wire to the outlet cable. The total power supply of the equipment shall be connected to the three-phase power outlet on the wall and should not be connected to the outlet of the wiring board. In order to reduce interference, power supply of surrounding equipment, mobile phone, and lifting platform should be turned off during inspection.

5.1.2 Inspection Room Requirements and Layout In visual electrophysiological examination, ffERG and EOG have strict requirements to the inspection room environment: the inspection room should be completely opaque, with dark, nonsmooth walls and ceilings, especially around doors and windows. You also need to set up isolation buffer compartments to prevent irrelevant people from straying in. If the door and window cannot

© People’s Medical Publishing House, PR of China 2022 R. Sui et al., Practical Visual Electrophysiological Examination, https://doi.org/10.1007/978-981-16-8910-9_5

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5  Visual Electrophysiology Equipment Install and Operation

102

Ground wire port and ground wire

a

b

Fig. 5.1  Ground wire connection of isolated power box. (a) Connect special ground wires; (b) isolation power box Fig. 5.2  Ground wire connection diagram

enclosed, we can use thick shading cloth to make pass top to reach ground to isolate a space, in order to enclose the flash stimulator, leave patient and operator space. Figure 5.3 is a schematic diagram of the layout of the examination room.

5.2

 VEP Operation Steps P and Key Points

This section refers to the ISCEV VEP 2016 international standard.

5.2  PVEP Operation Steps and Key Points

103

5.2.1.3.2  Input Patient Information The date of birth of the patient should be entered accurately (Fig.  5.4) in order to compare the results with the built-in normal reference value of the corresponding age group. 5.2.1.3.3  Electrodes Placement

Fig. 5.3  Layout of the eye electrophysiological examination room

5.2.1.3.3.1  Determine the Positions of Electrodes Placement

5.2.1.1 Examination of Environmental Requirements PVEP should be examined in natural indoor light or weak light. Darkroom is not required, and the light source cannot directly illuminate the patient’s field of vision. The examination environment in the same examination room should be consistent.

The PVEP electrodes are skin electrodes, and the placement of the electrodes must be accurate (Fig.  5.5). According to the international standard 10/20 system, the active electrode is located at 10% on the occipital tuberosity side of occipital tuberosity—nasal root line (OZ), that is, occipital cortex position. The reference electrode is located at the 30% site (FZ) on the nasal root side of the above line, that is at the hairline. The grounding electrode may be located in one of the following locations: the forehead, the apex (the midpoint of the occipital tuberosity—nasal root line), the mastoid process, or the earlobe.

5.2.1.2 Preexamination Preparation

5.2.1.3.3.2  Clean the Skin

5.2.1 PVEP Examination for Adult

5.2.1.2.1  Patient Preparation Before PVEP examination, the patient should not be dilated or contracted the pupil and should be kept the pupil in its natural state. If the patient is dilated the pupil, the stimulation pattern cannot form a clear image on the retina and the ideal waveform cannot be recorded. PVEP examination is required to achieve the best corrected vision of the patient. The patient should have optometry before the examination and wear glasses during the examination in order to obtain the best corrected vision of the patient. 5.2.1.2.2  Examination Distance In patients with PVEP, the distance between the eye and the graphic stimulator should be 1 m.

5.2.1.3 PVEP Examination Operation Steps

Use a special skin cleanser to clean the skin where the electrodes are to be placed. Rub it vigorously to remove oil from the skin surface (Fig. 5.6). If possible, ask the patient to wash his/ her hair on the examination day morning and not to use cosmetics. 5.2.1.3.3.3  Connect the Electrode to the Amplifier

Silver–silver chloride or gold cup skin electrodes are used for VEP. Generally, PVEP can only be monocularly examined, and three skin electrodes should be placed. Generally, wires with different colors are used to distinguish the electrodes: the active electrode is red, the reference electrode is blue, and the grounding electrode is black. Each of the three electrodes is connected to the port of the corresponding color of the external amplifier (Fig. 5.7). The system default amplifier channel is Channel 1. 5.2.1.3.3.4  Electrodes Placement

5.2.1.3.1  Open PVEP Program Switch on the visual electrophysiological device and open the PVEP program.

First, dip the electrode into the electrode conductive paste and pay attention to filling the conductive paste with the corresponding elec-

104

5  Visual Electrophysiology Equipment Install and Operation

Fig. 5.4  Patient information input window

Fig. 5.5  Schematic diagram of VEP electrodes positions

Fig. 5.6  Skin cleaning method

trode cup (Fig. 5.8). After that, the three electrodes are placed at corresponding positions successively (see Fig. 5.5) and fixed with adhesive tape.

5.2.1.3.4  Impedance Measurement Click impedance to test the impedance of the active electrode and the reference electrode (Fig. 5.9). Visual electrophysiological examina-

5.2  PVEP Operation Steps and Key Points

Fig. 5.7  Skin electrode connection port

105

tion requires both the impedances should be less than 5  k Ω. If two electrode impedances are higher than 5 k Ω, need to clean skin of grounding electrode position again. The effect of active electrode and reference electrode impedance difference should be less than 1 k Ω. If one of the electrode impedances is higher than 5 k Ω, only to clean skin of this related electrode position. 5.2.1.3.5  Electrode Fastened After the impedance meets the requirements, the electrodes can be fastened with a headband. 5.2.1.3.6  Monocular Cover The examination should first examine the right eye and then the left eye. Cover the contralateral eye during monocular examination. Use a black eye patch or lens frame with black patch to cover.

Fig. 5.8  Skin electrode conductive paste

Fig. 5.9  Impedance test interface

5.2.1.3.7  Refractive Correct Corrective lenses are placed according to the results of 1  m away best corrective vision examination.

106

5  Visual Electrophysiology Equipment Install and Operation

5.2.1.3.8  PVEP Examination 5.2.1.3.8.1  PVEP Examination of Right Eye

Click Start at the bottom right of the software to start the examination (Fig. 5.10). Exam the 1° spatial frequency twice and the 15′ spatial frequency twice. PVEP sampling averages number (avgs) need to more than 50 times, the artifact (artif) is caused by patients blinking or improper, and the fewer number of artifact, the better result. 5.2.1.3.8.2  PVEP Examination of Left Eye

After the right eye examination, change to cover the right eye. Perform the same procedure for the left eye, examining 1° and 15′ spatial frequencies twice. 5.2.1.3.9  Results Analyses After the examination, click analysis in the menu above, as shown in Fig. 5.11, to view the waveform. Note the upper left ruler, PVEP generally selects 10  μV/div, and the ruler can be adjusted by “+” or “–” in the lower right. Check the corresponding identification, especially

Fig. 5.10  PVEP recording interface

whether N75 and P100 are marked at the corresponding trough and peak. If not, manual adjustment is required. Click save examination and click print out.

5.2.2 PVEP Examination for Children The PVEP examination procedure for children is the same as adults. In order to attract the fixation of children, cartoon patterns are used for fixation. Young children who cannot cooperate with fixation can be used with handheld graphic stimulator.

5.2.2.1 Special Stimulator 5.2.2.1.1  C  artoon Fixation Pattern Suitable for Children PVEP requires the child to cooperate with fixation, and the patient’s parents can hold the child and let the child look ahead for examination. You can debug the cartoon fixation pattern to attract children (Fig. 5.12).

5.2  PVEP Operation Steps and Key Points

107

Fig. 5.11  PVEP analysis interface

a

b

Fig. 5.12  PVEP stimulus checkboard with cartoon fixation pattern

5.2.2.1.2  Handheld Graphic Stimulator For children under 2 years old, the pattern handheld (PHH) can be used. The examination distance is 50  cm, the diameter of the stimulus

pattern checkerboard is 9  mm, and the vision angle is 1° (Fig. 5.13). The PHH results are similar to those obtained by the general stimulator (Fig. 5.14).

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5  Visual Electrophysiology Equipment Install and Operation

Fig. 5.13  PVEP handheld graphic stimulator (PHH) examination scene

Fig. 5.14  PVEP handheld graphic stimulator (PHH) examination results

5.2.2.2 Special Skin Electrode Disposable 3M skin electrodes are also an option for VEP testing in children (see Fig. 2.11). This

electrode has the advantages of good adhesion, not easy to fall off, low impedance, suitable for children.

5.3  FVEP Operation Steps and Key Points

5.3

 VEP Operation Steps F and Key Points

5.3.1 FVEP Examinations for Adult The operation steps and precautions of FVEP examination are basically the same as those of PVEP, with the main differences in the following two points: (1) the stimulator is a flash stimulator, and the patient’s head is placed in the head holder of the flash stimulator and (2) FVEP eye mask should be tight and opaque. FVEP stimulus frequency commonly is 1 Hz, and the examination is repeated three times (Fig.  5.15). The results of FVEP examination focus on the evaluation of P2 wave amplitude and peak time. Generally, P2 should be labeled with the first peak after 100 ms, and there are only a few special cases where P2 peak 8 Hz) according to the situation. The steady-state response should observe the amplitude of the second positive

109

wave, N2 and P2 should be marked in the corresponding trough and peak. It is also necessary to be observed the signal-to-noise ratio (SNR). SNR greater than 3 indicates that the corresponding waveform is an effective signal, not a noise interference wave.

5.3.2 F  VEP Examinations for Infant and Young Children The infant and young children FVEP procedure differs from the adult FVEP procedure in that several special stimulators are suitable for the children.

5.3.2.1 Handheld Controlled Infant Flash Stimulator FVEP can be performed with a handheld, real-­ time controlled BabyFlash stimulator while children awake to avoid the inhibitory effect of anesthesia on the optic nerve. Parents can hold their child when using BabyFlash, and the child can be examined with open eyes. The stimulator can follow the child and provide flash stimulation

a

Fig. 5.15  FVEP examinations results. (a) 1 Hz FVEP examination results; (b) FVEP examinations results of 12 Hz high-frequency stimulation

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5  Visual Electrophysiology Equipment Install and Operation

b

Fig. 5.15 (continued)

lid opener or be assisted in eyelid opening. The advantage of this stimulator is relatively easy to operate.

Fig. 5.16  FVEP handheld controlled flash stimulator BabyFlash examination scene

when the child opens eyes. The examination distance between the tested eye and the stimulator is 15  cm (Fig.  5.16). The examination results are shown in Fig. 5.17.

5.3.2.2 Flat Full-Field Ganzfeld Stimulator Unlike BabyFlash, the flat full-field Ganzfeld stimulator is used to examine children after anesthesia (Fig. 5.18). Since the child is not awake, an eyelid opener is required, or operating physician is required to open the eyelids. The advantage of the full-field Ganzfeld stimulator over the handheld stimulator is that the stimulation range is wide and more close to international standards. 5.3.2.3 Mini-Ganzfeld Handheld Flash Stimulator After anesthesia, children can also be used for mini-ganzfeld handheld flash stimulator for examination. Children also need to be used eye-

5.3.2.4 Eye Mask Stimulator After anesthesia, children can be used for eye mask stimulator (flash goggle). Children close eyes for examination, the amplitude is low. 5.3.2.5 Kooyman Electrode Stimulator Kooyman electrode stimulator can be used for children after anesthesia, and the eye can be opened by the Kooyman electrode itself.

5.4

 ERG Operation Steps ff and Key Points

This section refers to the ISCEV 2015 ffERG international standard.

5.4.1 ff  ERG Electrode Operation Points and Notes ffERG active electrodes must contact the cornea, conjunctiva, or the skin of the lower eyelid. Clinically available active electrodes include Burian-Allen electrodes, corneal contact lens electrodes, conductive fiber electrodes, gold foil electrodes, HK-Loop conductive metal ring elec-

5.4  ffERG Operation Steps and Key Points

111

Fig. 5.17  FVEP handheld controlled flash stimulator BabyFlash examination results

need to be averaged up to three times to obtain reliable results, more times averages could destroy the dark-adaptation condition, and induce more cone response. Skin electrodes placed on the lower eyelid are not suitable for recording weak pathological ffERG signals except that the patients can’t cooperated such as children. Weak ffERG signals from the skin of the lower eyelid are better to be used to evaluate the retinal funcFig. 5.18  Flat full-field Ganzfeld stimulator examination tion than no wave because patient cannot accept scene the cornea contact lens electrodes. The ffERG recording electrode is exposed to trodes, Kooyman electrode, and skin electrodes. tears during use, and proper cleaning and disinThe corneal contact lens electrode is transparent fection must be taken after each use. Cidex OPA in the center and relatively larger contact area (classified as a high-level disinfectant) is recomwith the cornea, so this electrode records the mended because most if not all sterilization highest and most stable ffERG amplitude except methods(such as steam and ethylene oxide gas) Burian-Allen electrodes, which is too expensive. will damage or destroy parts that make up the During ffERG examination, most active elec- majority of the ffERG electrode, and the cornea trodes need to touch the cornea, and the conduc- electrodes should be soaked in cidex OPA for tive medium is different from skin electrodes: in 5  min, then it can get the disinfecting effect. addition to considering electrical conductivity, Disposable electrodes are excluded. special attention should be paid to corneal proAccording to the instruction of HK-Loop tection. Therefore, it is needed to use a non-­ electrode, it can be sterilized by gas steam at high irritant, non-sensitizing ionic conductive temperature and high pressure. And its ffERG medium, such as containing sodium chloride amplitudes maybe be 2/3 of amplitudes by ERG-­ contact lens care solution or artificial tears, less Jet electrodes. than 0.5% methylcellulose eye drops. Topical The ffERG reference electrode can be a bipoanesthesia is required prior to the use of the cor- lar electrode, as Burian-Allen electrode, inteneal contact lens electrode. grated with the contact lens electrode, which The signals recorded by the ffERG active has the most stable signal. The ffERG reference electrode placed on the surface of the cornea electrode is usually a separate reference elec-

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5  Visual Electrophysiology Equipment Install and Operation

trode matched with the unipolar contact lens electrode, and the amplitude is usually large enough. The independent reference electrode should be placed on the orbital edge of the corresponding temporal side of the eye, not on the muscle. The 2015 ISCEV ffERG standard states that grounding electrodes can be placed on the earlobes, mastoid process, or forehead.

5.4.2 P  repare Before ffERG Examination The pupil should be dilated to the maximum before ffERG examination, and the pupil size should be recorded before and after the examination. It takes 20  min for dark adaptation before recording dark adaptation ERG (completely opaque darkroom), and 10 min for light adaptation before recording light adaptation (head placed in standard background light Ganzfeld). After dark adaptation, corneal contact lens electrode should be installed under weak red light, avoid strong red light or white light, and then close the weak red light and dark adaptation for 5  min after electrode installation. Dark adaptation responses should be checked in order from weak to strong intensity of stimulus light. Fluorescein fundus angiography, fundus photography, or other strong light stimulator imaging should be avoided before examination. If these tests have been performed, the patient should recover in normal indoor light for at least 30 min before beginning dark adaptation. After the patient’s dark adaptation, the examination can begin after the preparation of the above electrodes and articles.

5.4.3 ff  ERG Examination Operation Steps ffERG is generally binocular synchronous examination. Impedance testing is not recommended after corneal electrodes are installed.

Open ffERG program and input patient information, select accordingly dark adapted 0.01 ERG, dark adapted 3.0 ERG, dark adapted oscillatory potential, dark adapted 10.0 ERG, generally record once for each stimulation, up to three times, corresponding interval time between two times flash stimulating are, respectively, 2 s (0.01 dark adapted ERG), 10 s (3.0 ERG dark adaptation and dark adaptation 3.0 oscillatory potential), 20  s (10.0 dark adapted ERG). See Figs.  5.19, 5.20, 5.21, 5.22, 5.23, and 5.24, respectively. After the examination of the above dark-­ adapted responses, click on light adapted 3.0 ERG, and the full-field Ganzfeld background light will be automatically turned on, and the 10-min timer will be automatically turned on. The patient’s head will be placed on the full-field Ganzfeld head holder, and the patient will be instructed to open his/her eyes, light adaptation for 10  min, and the corneal electrode can be removed. After the adjustment of light adaptation, corneal electrodes were re-installed, and light adapted 3.0 ERG and light adapted 30  Hz flicker ERG are examined successively, as shown in Figs. 5.23 and 5.24.

5.4.4 ff  ERG Result Analysis and Marker Adjustment After the above light adapted examination, click the menu analysis, and click save examination on the top right. Check the six ERG results in turn in the analysis interface to see whether the marker is in the corresponding trough and peak. If the marker is not at correct position, it must be moved manually, especially as to the oscillatory potential and the 30 Hz flicker light-adapted response, it is necessary to move the marker to the corresponding trough and peak one by one. It is also necessary to adjust the vertical scale of each step by means of + and – in the lower right. Generally, the vertical scale of each step should be fixed to a reasonable scale, so that the abnormal result is more intuitive. See Figs.  5.25, 5.26, 5.27, 5.28, 5.29, and 5.30 for the corresponding scale of each step.

5.4  ffERG Operation Steps and Key Points

Fig. 5.19  Dark adapted 0.01 ERG recording interface

Fig. 5.20  Dark adapted 3.0 ERG recording interface

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5  Visual Electrophysiology Equipment Install and Operation

Fig. 5.21  Dark adapted 3.0 oscillatory potential recording interface

Fig. 5.22  Dark adapted 10.0 ERG recording interface

5.4  ffERG Operation Steps and Key Points

Fig. 5.23  Light adapted 3.0 ERG recording interface

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5  Visual Electrophysiology Equipment Install and Operation

Fig. 5.24  Light adapted 30 Hz flicker ERG recording interface

Fig. 5.25  Dark adaptation 0.01 ERG analysis interface. The reasonable vertical scale is 200–250 μV/div according to the corresponding normal values range

5.4  ffERG Operation Steps and Key Points

117

Fig. 5.26  Dark adaptation 3.0 ERG analysis interface. The reasonable vertical scale is 200–250 μV/div according to the corresponding normal values range

Fig. 5.27  Dark adaptation 3.0 oscillatory potential analysis interface. N1, P1, N2, P2, N3, P3, N4, P4 should be marked and the amplitudes of each wave or the sum of the

three waves should be observed. The reasonable vertical scale is 50–100  μV/div according to the corresponding normal values range

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Fig. 5.28  Dark adapted 10.0 ERG analysis interface. The reasonable vertical scale is 200–250 μV/div according to the corresponding normal values range

Fig. 5.29  Light adapted 3.0 ERG analysis interface. The reasonable vertical scale is 100–150 μV/div according to the corresponding normal values range

5.4  ffERG Operation Steps and Key Points

119

Fig. 5.30  Light adapted 30  Hz flicker ERG analysis interface. The reasonable vertical scale is 100–150 μV/div according to the corresponding normal values range. N1,

P1, N2, P2, N3, P3, N4, P4 should be marked to observe the amplitude of P2 wave or the mean amplitude of three typical waves (except P1 wave)

5.4.5 ff  ERG Examination for Infants and Young Children

orally. According to the indications, the examination should follow the medical guidelines to choose sedatives, retardants, or general anesthesia. Sedation and light anesthesia does not affect ffERG amplitude, general anesthesia may affect ffERG [1].

5.4.5.1 Examination Characteristics Recording baby ffERG is very important, but very difficult. ffERG in infancy requires special examination methods and values, but the waveform and amplitude of ffERG during late infancy and childhood are close to adults. Dark adaptation ERG in infants aged 6–12 months and light adaptation ERG in infants aged 2–3 months had lower ERG amplitudes and longer peak times. Dark adaptation 3.0 ERG in healthy infants younger than 6 months is difficult to determine, but dark adaptation 10.0 ERG in infants without retinal disease at any month is generally easier to determine [1]. 5.4.5.2 Anesthesia Many pediatric patients require sedation or general anesthesia to test ffERG, infants can be swaddled, and children between the ages of 2 and 6 years who do not cooperate can be sedated

5.4.5.3 Electrode It is best to use a corneal contact lens electrode with eyelid opener for infant ffERG active electrode, and the corresponding child size electrode should be selected. DTL electrode can be used, too children are easy to cooperate and it costs less, but the amplitude is about 1/2 of that recorded by the contact lens electrode. HK-loop ring and Gold foil electrodes can be selected for children, too, their amplitudes are about 2/3 if that by the contact lens electrodes. 5.4.5.4 Repeating Time The ffERG examinations for infants have a large variation and need to be repeated 2–3 times to ensure the reliability of the results.

5  Visual Electrophysiology Equipment Install and Operation

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5.4.5.5 Stimulators Infant binocular ffERG can be checked using a rotatable electric lift bracket with a flat Ganzfeld full-field flash stimulator. The 2015 edition ISCEV ffERG standard states that the ffERG full-field Ganzfeld stimulus must be able to provide uniform brightness throughout the subject’s detection field. This is usually done with a dome or full sphere design. After anesthesia, patients in bed can only fully meet the requirements of international standards by using full-field Ganzfeld examination, so as to obtain reliable examination results. ffERG can be checked binocular synchronously with full-field Ganzfeld examination, without the need for binocular sequential dark adaptation and light adaptation, and it is fast and convenient. See Figs. 5.18 and 5.31. After anesthesia, infant ffERG examination can also be carried out with handheld mini-­ ganzfeld, which is more convenient to operate, requiring monocular examination, firstly right eye dark adaptation, secondly left eye dark adaptation, thirdly right eye light adaptation, and lastly left eye light adaptation as sequential examination. As shown in Fig. 5.22.

5.5

 ERG Operation Steps P and Key Points

This section refers to the ISCEV 2012 edition PERG international standard.

5.5.1 P  repare Before PERG Examination The pupil should not be dilated before the examination, and fluorescein fundus angiography and fundus photography should not be performed before the examination. If these examinations have been performed, the patient should recover in the general lighting room for at least 30 min, and the pupil size should be recorded. Before the examination, the patient should obtain the best corrected vision at 1  m away from the examination. The patient should not wear multifocal or progressive glasses. During the examination, the patient should

relax his/her muscles and keep natural light indoors. The light source should not directly stimulate the screen and the patient’s eyes [6].

5.5.2 P  ERG Electrode Operation Key Points 5.5.2.1 Electrodes and Positions The PERG active electrode should be in contact with the cornea or the conjunctiva of the lower bulb, so the retinal imaging should not be affected, and the contact lens electrode should not be used. Fiber electrode, gold foil electrode, or HK-loop ring electrode can be selected. Electrodes should be placed carefully and uniformly to reduce possible artifacts. 5.5.2.2 Fiber Electrode The fiber electrode should be in contact with the eyeball, preferably on the upper edge of the lower eyelid. The thin fiber electrode can be placed in the lower conjunctival sac, which helps to reduce variation between patients but results in a lower amplitude (Fig. 5.32). 5.5.2.3 Gold Foil Electrode The gold foil electrode should be placed directly below the middle of the pupil. The electrode should be in a straight line with the connector, not touching the skin. 5.5.2.4 HK-Loop Ring Electrode The loop electrode should be placed in the lower vault of the conjunctiva by the ring, and the loop electrode should be foldable to ensure that the electrode-sensitive windows are in contact with the bulbar conjunctiva 5  mm below the eyelid margin, the loop electrode is not in contact with the cornea. 5.5.2.5 Others The skin electrode cannot be used as a PERG recording electrode because the amplitude is too low. The independent reference electrode should be placed at the corresponding lateral canthus. The forehead is the classic grounding electrode position, other parts are acceptable.

5.5  PERG Operation Steps and Key Points

Fig. 5.31  ffERG (DTL active electrode) examination results of infants

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5  Visual Electrophysiology Equipment Install and Operation

Fig. 5.31 (continued)

5.5.3 P  ERG Examination Stimulus Conditions PERG needs to average at least 100 times, and it can average up to 300 times if the signal is weak.

Repeat twice to improve examinations reliability. See Figs. 5.39 and 5.40. The black and white checkerboard visual angle of PERG stimulation is 48′, and the minimum visual field of stimulation is 15°. The

5.6  mfERG Operation Steps and Key Points

standard PERG stimulus frequency is 2 Hz transient response.

5.5.4 P  ERG Examination Operation Steps PERG examination procedures are basically similar to VEP, specific software procedures refer to the VEP section. The PERG recording interface and analysis interface are shown in Figs. 5.33 and 5.34.

123

5.5.5 PERG Examination for Children PERG examination for children is difficult, children who can cooperate with fixation can be used cartoon fixation patterns to attract attention, generally, children over 2 years old may cooperate with the examination. The electrodes are the same as adults.

5.6

 fERG Operation Steps m and Key Points

This section is based on the ISCEV 2021 mfERG international standard.

5.6.1 P  repare Before mfERG Examination

Fig. 5.32  DTL fiber electrode placement diagram

Fig. 5.33  PERG recording interface

The pupil of the patient should be dilated before examination and the pupil size should be recorded. The patient should be prepared in the ordinary indoor lightroom before the examina-

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5  Visual Electrophysiology Equipment Install and Operation

Fig. 5.34  PERG analysis interface

tion. If fluorescein fundus angiography and fundus photography were performed before the examination, the patient should restore for 15 min. In principle, ametropia within ±3 diopters does not affect the results of mfERG examination, and ametropia outside this range should be corrected at the examination distance (usually 26  cm) for optimal vision. Corrective lenses should not affect the patient’s field of vision. The indoor environment requires as same as that of VEP and PERG.

5.6.3 mfERG Operating Essentials

5.6.2 mfERG Electrode Requirements

5.6.4 mfERG Steps

The mfERG active electrode can be corneal contact lens electrode, fiber electrode, HK-loop electrode, or gold foil electrode, which needs to contact cornea or conjunctiva. Corneal contact lens electrode transparent lens should be in the middle of the pupil, cannot block the patient’s sight. Electrode location and precautions are the same as that of ffERG.

mfERG should be examined with one eye, and the patient should maintain good fixation. Fixation mark should be a fine forked line, which cannot block the field of vision in the central position. Generally, 61 or 103 hexagon stimuli are selected for mfERG. The 61 hexagon stimuli can be checked for 4 cycles, while the 103 hexagon stimuli need 8 cycles.

After the electrode is installed, the patient can start the examination with binocular synchronization or one by one. See Figs. 5.35, 5.36, and 5.37. At the end of each cycle, check whether the fixation is good by the high amplitude density of the central region to decide to accept or reject the result of each cycle. mfERG needs to be highly compatible with fixation, and children cannot be examined without it.

5.7  EOG Operation Steps and Key Points

5.7

 OG Operation Steps E and Key Points

This section refers to the EOG international standard of ISCEV 2017.

5.7.1 P  reparation Before EOG Examination

125

fundus angiography and fundus photography should not be performed before the examination. The pupil of the patient should be dilated to the maximum. Vision correction is not required. Before the formal examination, ask the patient not to turn head, but to turn eyes to the left or right side and fix on the light. It is necessary to practice before the examination, and it should get a stable and high-quality waveform before the formal examination.

Patients should adapt to natural light for at least 30  min before the examination, and fluorescein

a

b

Fig. 5.35  mfERG patient examination scenario. (a) mfERG examination of ordinary graphic stimulator. (b) mfERG examination of SLO precise graphic stimulator

a

Fig. 5.36  mfERG examination interface. (a) Ordinary mfERG, (b) precise mfERG

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5  Visual Electrophysiology Equipment Install and Operation

b

Fig. 5.36 (continued)

Fig. 5.37  mfERG analysis interface

5.7.2 EOG Electrode Requirements The EOG recording electrode can be a silver chloride electrode or a gold cup electrode. EOG

requires two recording electrodes per eye (no distinction between active electrodes and reference electrodes). Two recording electrodes in the right eye are connected to the amplifier channel 1 and placed in the outer canthus and the inner canthus

5.9  Different ERG Electrodes Comparing

127

of the right eye. The two recording electrodes in the left eye are placed in the outer canthus and the inner canthus of the left eye with the amplifier channel 2. Two electrodes in the inner canthus of both eyes are located equidistant from each other on either side of the nose. Both eyes share a grounding electrode, which can be placed on the forehead, top, earlobe, or mastoid. As shown in Fig. 5.38.

50 s of rest is taken at intervals. Then light adaptation examination is conducted for 15 min, with the same interval as before. During light adaptation, if the light peak waveform has been observed, the examination can be stopped. The inspection results are shown in Figs.  5.39 and 5.40. Children who cannot follow fixation cannot take EOG examination.

5.7.3 EOG Operation Steps

5.8

Dark adaptation examination is conducted for 15 min and recorded for 10 s in each minute, and

Visual Electrophysiological Examinations Operation Key Points Comparing

Table 5.1 summarizes the main operating points of common electrophysiological examination items.

5.9

Fig. 5.38  Electrode position of EOG patients

Fig. 5.39  EOG recording interface (dark adaptation)

 ifferent ERG Electrodes D Comparing

Table 5.2 summarizes the main features of different ERG electrodes

5  Visual Electrophysiology Equipment Install and Operation

128

Fig. 5.40  EOG analysis interface

Table 5.1  Comparison of main operating points of different eye electrophysiological examination items Items The indoor environment The pupil

PVEP Natural light Natural pupil

FVEP Natural light Natural pupil

ffERG Absolute dark room Dilate the pupil to the maximum

PERG Natural light

mfERG Natural light

EOG Absolute dark room Dilate the pupil to the maximum No

Natural pupil

Dilate the pupil to the maximum

Refractive correct Recording electrode

Yes

No

No

Yes

Yes

Silver chloride electrode, gold cup electrode

Silver chloride electrode, gold cup electrode

Fiber electrode, gold foil electrode, HK-loop ring electrode

30 min

30 min

30 min

Corneal contact lens electrode, fiber electrode, gold foil electrode, HK-loop ring electrode 15 min

Silver chloride electrode, gold cup electrode

Natural light acclimation time before examination Advance dark adaptation or light adaptation

Corneal contact lens electrode, fiber electrode, gold foil electrode, HK-loop ring electrode, etc. 30 min

No

No

Dark adaptation 20 min, light adaptation 10 min

No

No

No

30 min

Amplitude

ffERG/mfERG Commonly used, higher amplitudes Alcohol/Cidex OPA Single use/ Alcohol/ Cidex OPA 100% 89%

Application Feature Disinfection

ERG-Jet

Burian-Allen

Electrode Picture

Table 5.2  Comparison of main features of different ERG electrodes Gold Foil

fERG/mfERG/PERG Comfortable, lower amplitudes Gas sterilization or Alcohol/Cidex OPA autoclaving 77% 56%

HK-Loop

46%

Single use

DTL

12%

Single use/reused

Skin

5.9  Different ERG Electrodes Comparing 129

6

ISCEV Extended Visual Electrophysiological Examinations

6.1

Objective Visual Acuity-VEP SF Limit

In 2020, ISCEV released the objective visual acuity related extended protocol, Sweep VEP’s new standardized name is VEP spatial frequency limit (as VEP SF limit), and it is clinically used to check the objective vision of patients who cannot cooperate with subjective vision examination. Patients do not need subjective coordination, but they need to look at the stimulus screen. The stimulus pattern was 10–13 vertical grating with different spatial frequencies, and the study confirmed that this kind of stimulus pattern had the best correlation with visual acuity. The stimulation frequency is 7.5  rps, which is a steady-state response, and the waveform is sinusoidal, which is relatively stable. The check distance is 1  m or 80–90  cm according to the real test, the electrode is same as VEP. The patient can take a break during the examination. The examination results can be automatically calculated to obtain decimal vision. The data with large variation in the original results can be deleted, and the visual acuity results can be obtained from at least three valid data. The amplitude SNR of the effective data should be greater than 3. The amplitude of the minimum spatial frequency for patients with normal vision is not the maximum. The amplitude from low spatial frequency to high spatial

frequency first goes from low to high, and then gradually decreases until it approaches the noise level. In this process, there will be a threshold frequency, and the examination can be stopped when the threshold frequency is showed (Figs. 6.1, 6.2, 6.3, and 6.4).

6.2

ON/OFF PVEP

ON/OFF PVEP refers to presentation/withdraw graphics PVEP, which is clearly indicated in the international standard of ISCEV VEP to be used for patients with nystagmus and other poor coordination, with a lower requirement for fixation and a more stable result than ordinary PVEP [2].

Fig. 6.1  Sweep VEP stimulus pattern

© People’s Medical Publishing House, PR of China 2022 R. Sui et al., Practical Visual Electrophysiological Examination, https://doi.org/10.1007/978-981-16-8910-9_6

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6  ISCEV Extended Visual Electrophysiological Examinations

132

Fig. 6.2  Original waveform of VEP SF limit examination results. In this case, the first curve (1–8) and the tenth curve (SNR  >  3) in the corresponding waveform of 12

stimulus frequencies were basically normal, while the other three curves (SNR 5 μV, C2/C3 amplitude >10 μV)

(d) pathway and can be used to diagnosis complete and incomplete CSBN, melanoma-associated retinopathy, part of autoimmune retinopathy, X-linked retinoschisis, Batten disease, Duchenne muscular dystrophy, spinocerebellar degenera-

tion, quinine toxicity, and other retinal disorders. The recommended stimulus light is orange at 625 nm 200 ms, and the background light is green at 525  nm 200  ms. The operation steps are the same as ffERG (Fig. 6.13) [14].

6  ISCEV Extended Visual Electrophysiological Examinations

136

6.10 Multifocal Visual Evoked Potential

Fig. 6.7  Locations of three channel VEP electrodes

6.9

PERG+PVEP Simultaneous Examination

PERG+PVEP synchronous examination is the same spatial frequency black and white checkerboard pattern stimulation, PVEP electrode and PERG electrode use, respectively, an amplifier channel to achieve PVEP and PERG synchronous detection. PERG+PVEP can be performed in children with poor coordination of PERG and nystagmus (Fig. 6.14).

Multifocal visual evoked potential (mfVEP) records brain occipital cortex site potential reaction. The stimulation of each area in the visual field is controlled by the computer alternately (or partially overlapped), and the correlation function of stimulus signal and response signal is calculated through digital signal processing. The computer extracts and obtains the responses of each area in the visual field in a short time record. mfVEP test can objectively evaluate visual field and visual pathway function. The stimulation pattern is the nasal target shape stimulation (Fig. 6.15), which is designed for glaucoma examination and corresponds to the nasal step in the visual field. There are ten electrodes in the four channels, and the positions are shown in Fig. 6.16 and fixed electrodes cross, which asbestos ports should be soaked in saline before installing, can be used as the Fig. 6.15. The examination distance is 24 cm and the radius of the field of vision is 30°. The examination results can be compared with the static perimetry. Four original plot waveforms are obtained from the four channels, and then the fifth channel is fitted, which is the final mfVEP examination result. The mfVEP objective field examination for glaucoma is shown in Fig. 6.17.

6.10  Multifocal Visual Evoked Potential

Fig. 6.8  ON/OFF PVEP examination result waveform of three channels. In this case, the results of the three channels were repeated twice, with good repeatability and reli-

137

able results. The examination results of the three channels were also consistent, which belonged to the normal waveform

138

6  ISCEV Extended Visual Electrophysiological Examinations

Fig. 6.9  Three-channel FVEP inspection result waveform. The results of three-channel FVEP should be observed in two and three channels, namely the right eye

2, 3, left eye 5, 6 in the figure. The waveform consistency is not albinism, and the waveform inconsistency may be albinism

a

Fig. 6.10 (a) Patient S-cone ERG examination result waveform. S-cone ERG was observed the amplitude of LM and S wave, which in this case was from the different background as 1, 2 lines for 30 cd/m2 590 nm amber, 3, 4 lines for 560 cd.ms, and same stimulus as 0.1 cds/ m2 470 nm blue 2 ms. And the right eye is recorded from

HK-Loop electrode, and the left eye was recorded from ERG-Jet electrode. (b) Mouse S-cone ERG examination result waveform. The stimulus is 3, 3.8, 6, 10 μWs/cm2 365 nm UV 5 ms, the background is 20 cd/m2 white light and light adaptation time is 10 min. The average time is 50

6.10  Multifocal Visual Evoked Potential

b

Fig. 6.10 (continued)

139

140

6  ISCEV Extended Visual Electrophysiological Examinations

Fig. 6.11 PhNR ERG examination result waveform. PhNR ERG is observed the negative wave after b wave. In this case, the different stimulus is 1, 2 lines from 0.3 cds/ m2 625 nm red, 3, 4 lines from 1.0 cds/m2 625 nm red, and

5, 6 lines from 3.0 cds/m2 625 nm red, and the background is 10 cd/m2 470 nm blue. And the right eye is recorded from HK-Loop electrode, and the left eye was recorded from ERG-Jet electrode

6.10  Multifocal Visual Evoked Potential

141

Fig. 6.12  The stimulus-response series for the dark-­ gradually increased during the stimulus light intensity adapted ffERG examination result waveform. In this case, from 0.0003 to 3 cd s/m2, and the amplitudes decreased the amplitude of positive b wave and oscillatory potential from 10 to 100 cd s/m2

142

6  ISCEV Extended Visual Electrophysiological Examinations

Fig. 6.13  ON/OFF ERG examination result waveform. In this case, the different stimulus is 1, 2 lines from 32 cd/ m2 590 nm amber 200 ms on/off, 3, 4 lines from 42 cd/m2 590 nm amber 200 ms on/off, 5, 6 lines from 64 cd/m2 590 nm amber 200 ms on/off, and 7, 8 lines from 250 cd/m2

590 nm amber 200 ms on/off, and the background is same as 30 cd/m2 525 nm green. And the right eye is recorded from ERG-Jet electrode, and the left eye was recorded from HK-Loop electrode

6.10  Multifocal Visual Evoked Potential

Fig. 6.14  PERG+PVEP simultaneous examination result waveform. In this case, the PVEP P100 amplitude of the right eye was 7.24 μV, with a peak time of 122.1 ms, the

Fig. 6.15  mfVEP stimulus pattern and mfVEP electrodes cross

143

PERG P50 amplitude was 2.22 μV, and the N95 amplitude was 3.99 μV, within the normal range

144

a

6  ISCEV Extended Visual Electrophysiological Examinations

b

Fig. 6.16  mfVEP electrode position. (a) Position of active electrodes and reference electrodes, (b) grounding electrode position

Fig. 6.17 mfVEP waveform of glaucoma. In this case, both the nasal superior and nasal inferior showed decreased amplitude of P1 wave, and the amplitude decreased area of the nasal superior was larger than the decreased area of the nasal inferior (red box area), showing objective glaucoma vision field changes of mfVEP in typical asymmetric

7

Visual Electrophysiological in Animal Experiments

Visual electrophysiology, as an evaluation method of objective visual function, is necessary for ophthalmic animal experiments. Animals are unable to carry out subjective visual function examination, so they must rely on objective visual function examination to evaluate the experimental results and the changes in animal visual function. ffERG, FVEP, mfERG, PVEP, and PERG can be used to quantitatively assess retinal and optic nerve function in animals of all sizes.

7.1

Hardware for Animal Visual Electrophysiological Examinations

The dedicated platform for animal experiments is used with full-field Ganzfeld and SLO multifocal stimulators (Fig. 7.1) for ffERG, FVEP, mfERG, PVEP, and PERG stimulation in large and small animals. The special operating table can be connected with the thermostatic device (Fig.  7.2). After anesthesia, the body temperature of small animals can be maintained to prevent transient refractive media opacity caused by hypothermia after anesthesia. After anesthesia, the animals are in the state of opening their eyes for a long time. In order to prevent corneal dryness, normal saline or artificial tears should be dropped on the cornea regularly. The operating table has an electrode

holder for easy electrode fixation and a push-pull device for easy inspection of animals in a stimulator.

7.2

Animal VEP

7.2.1 Animal PVEP Examination SLO stimulator is recommended for animal PVEP examination and its repeatability is better than that under TFT monitor. Under SLO stimulator, the target position of the fundus of the animal can be observed and found, and then the corresponding checkerboard stimulation is given. Because the animal cannot cooperate with fixation, it is difficult to get effective results. For animal PVEP examination, needle electrodes are used for the active electrode, reference electrode, and grounding electrode. The active electrode for small animals is placed subcutaneously at the midpoint between the ears (Fig. 7.3). The reference electrode (or used ring electrode) is placed under the tongue, and the grounding electrode is placed subcutaneously at the root of the tail. The location of the large animal electrode can be referred to the patient, as shown in Fig. 7.4. The examination procedure is the same as that of the patient. The monitor PVEP examination results are in one pig shown in Fig. 7.5.

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Fig. 7.1  Special operating table for animal experiments

Fig. 7.2  Thermostatic device for animal experiment

Fig. 7.3  PVEP electrode position of small animals

7.3  Animal ERG

7.2.2 Animal FVEP Examination The position of the animal FVEP electrode is same as above. The stimulator is generally a full-­field Ganzfeld stimulator, which can be checked by special push-pull operating table, as shown in Fig. 7.6. Because of the difficulty in controlling the position of the eyes after anesthesia, the normal

Fig. 7.4  PVEP electrode position in rhesus monkey

Fig. 7.5  Monitor PVEP examination results in one pig

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FVEP procedure rarely produces satisfactory results. Continuous stimulation light FVEP program can be set up for more ideal results.

7.3

Animal ERG

Animal ffERG is one of the most commonly used methods in ophthalmic research, which can objectively reflect the retinal function of experimental animals. The animal ffERG recording electrode is made of ring corneal electrode, the reference electrode, and the grounding electrode are made of needle electrode and are placed at the subcutaneous outer canthus of the eye and the subcutaneous root of the tail, respectively. The animal ffERG test is performed using a push-pull animal operating table, and the animal is pushed into the full-field Ganzfeld stimulator for examination. After anesthesia, the cornea and lens opacities caused by hypothermia in mice need to be kept warm on the operating table to avoid corneal and lens opacities, as shown in Fig. 7.7.

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Fig. 7.7  ERG examination scene of a mouse

human examination. Figure 7.9 shows the results of light adaptation ffERG in one pig.

7.3.3 Animals PERG Examination Fig. 7.6  FVEP examination of mouse

7.3.1 A  nimal Serial Dark Adaptation ffERG Response Examination Small animals can be examined by serial dark adaptation ffERG response to obtain the lowest  stimulus intensity that can produce ­ ERG w ­ aveform. It requires more than 12 h of dark adaptation before animals ffERG examination. The examination results are shown in Fig. 7.8.

7.3.2 A  nimals Light Adaptation ffERG Examination The light adaptation ffERG examination of larger experimental animals such as monkeys, pigs, and dogs can imitate the procedure and process of

PERG examination in animals is similar to PVEP, and SLO stimulator with fundus monitoring function is recommended and its repeatability is better than that under TFT monitor. The electrode position is the same as ffERG, DTL electrode, or ring electrode, which can be used as a recording electrode. It can be only checked for PERG in large animals with macula, as shown in Fig. 7.10.

7.3.4 Animals mfERG Examination SLO stimulator with fundus monitoring function is recommended for animal mfERG.  The electrode position is the same as ffERG, DTL electrode, or ring electrode, which can be used as recording electrode. When the fundus monitoring position is aligned with the part that needs to be inspected, the inspection can begin, as shown in Figs. 7.11, 7.12, and 7.13.

7.3  Animal ERG Fig. 7.8  Serial dark adaptation ffERG response examination results of mouse

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Fig. 7.9  Serial light adaptation ffERG examination result in pig

Fig. 7.10  Monitor PERG examination result of one pig

Fig. 7.11  mfERG examination scenario of rhesus monkey

7.3  Animal ERG

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Fig. 7.12  mfERG examination result in the modularized rhesus monkey with the abnormal local ERG as the red ring

Fig. 7.13  mfERG examination result in normal rat

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7.4

Animal Examination SOP

7.4.1 A  nimal FVEP Examination SOP [15, 16] 1.

2.

3.

4.

5.

6.

Dark adaptation There is generally no necessit for dark adaptation. If the detection of dark adaptation of FVEP rodents requires 2  h of dark adaptation, the following steps should be performed under weak red light. Anesthesia An intraperitoneal injection of 0.42  mg/kg chloral hydrate was given at 7%. Pupil dilation 0.5% tropinamide, start testing after 5 min of pupil dilation. Moisturizing During the whole experiment, 1 drop of 0.9% sodium chloride or artificial tear was synchronized binocularly every 2 min. Heat preservation During the preparation process of the experiment after anesthesia, the small animals are kept at a constant temperature of 37°. The thermostat can be turned off to reduce noise when stimulating. Electrodes In order to ensure the consistency of longterm multi-time VEP signal acquisition, stainless steel screw (axle diameter: 1.12 mm; Length: 3.18 mm) was implanted in the left visual cortex of the skull (1.5 mm left of the midline, 1.5  mm ahead of the lambda) at 1 week before first measurement, penetrating the cortex to about 1 mm, as the active electrode of right eye. The active electrode of left eye is connected to the right

Fig. 7.14  Animal FVEP implanted electrodes position

visual cortex. To measure, open the skin, clean the screw head to connect tissue and blood, and connect to the amplifier. After measurement, the wound was sutured and antibiotic ointment was applied. The aboveimplanted electrodes are as shown in Fig. 7.14. The active electrode can also be placed subcutaneously at the midpoint of the binaural connection using a needle electrode. The reference electrode is placed subcutaneously at the midpoint of the line between the two eyes with a needle electrode or under the tongue with a ring electrode. The grounding electrode is placed under the skin of the tail or hip with a needle electrode. The above electrodes position is as shown in Fig. 7.6. 7. Position In all experiments, the position of all animals on the animal table and the animal table position in the stimulator should be the same and marked as shown in Fig. 7.15. 8. Shelter Generally, the left eye is strictly covered when the right eye is detected. Then shade the right eye when examining the left eye. 9. Dark adaptation stimulus Turn off the thermostat and start the stimulus in the dark. A single stimulus is averaged for 50 times, with the stimulus intensity varying from weakness to strength. 1 0. Light adaptation The thermostat was turned on and the animals were placed in a stimulator with a fixed stimulus light intensity for 10 min. 11. Light adaptation stimulus Turn off the thermostat, and a single light adaptive stimulus can be averaged for 50 times.

7.4  Animal Examination SOP

Fig. 7.15 Animal table and animal position in the stimulator

7.4.2 A  nimal ffERG Examination SOP [17, 18] 1. Dark adaptation >12  h for rodent animal, >20  min for large animal. 2. Anesthesia Under low red light, the animals were weighed and injected intraperitoneally with 120 mg/kg ketamine and 10 mg/kg thiazine. 3. Pupil dilatation Under weak red light, 1 drop of 1% atropine was used simultaneously in both eyes. Start the experiment at least 5  min after applying the dilatation agent. If the dilatation is less

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than 5 min until the electrode is installed, turn off the red light and wait for 5 min to start the experiment. 4. Surface anesthesia Under weak red light, 1 drop of 0.5% procaine hydrochloride was used simultaneously in both eyes. 5. The coupling agent In low red light, 1 drop of 2.5% methylcellulose gel was used synchronously in both eyes. 6. Moisturizing During the experiment, 1 drop of 0.9% sodium chloride or artificial tear was used binocularly every 2 min. 7. Heat preservation During the experiment, the small animals were placed in a fixed position with a constant temperature of 37  °C to avoid opacity of refractive media caused by hypothermia after anesthesia. If there is noise, the constant temperature thermostat device can be turned off briefly when stimulated. 8. Electrodes (see as Figs. 7.7 and 7.16) Under weak red light, the corneal ring electrode was placed on the cornea of both eyes, and the appropriate ring electrode was selected according to the size of the eyelid. Generally, 3 mm diameter ring electrode is optional for mice. The contact area between the electrode and the cornea should be the same for all animals in all experiments. The reference electrode of binocular needle electrode was placed subcutaneously in the cheek of each pair of eyes, respectively. The grounding electrode is placed under the tail or hip. In general, 2 electrodes in the right eye are connected to the corresponding ports of channel 1 of the amplifier, 2 electrodes in the left eye are connected to the channel 2 ports and the ground electrode is connected to the middle port of the amplifier. 9. Positions In all experiments, the position of all animals on the animal table and the animal table position in the stimulator should be same and marked. The animal’s eyes should be positioned symmetrically to ensure that both eyes receive same light luminance.

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Fig. 7.16  Animal electrodes and animal table and thermostat

10. Dark adaptation stimulus After placing the electrodes, the animals were kept in the fixed position of the animal table, and the animal table was pushed to the internal fixed position of the stimulator. After the dilated pupil time reached 5 min, to turn off the thermostat to reduce noise, then start the series of stimuli. The average time of a single stimulus cannot exceed 3 times. The light intensity of the stimulus is from weak to strong. 11. Light adaptation The thermostat was turned on, and the animals were placed in the stimulator with fixed intensity and their eyes open for 10  min. Every 2 min, 1 drop of 0.9% sodium chloride or artificial tear was dropped in both eyes to keep the cornea moist. 12. Light adaptation stimulus Turn off the thermostat. A single light adaptive stimulus can be averaged 30–50 times.

7.4.3 A  nimal mfERG Examination SOP [19] 1.

Anesthesia 120 mg/kg ketamine and 10 mg/kg thiazide were intraperitoneally injected, and a retrobulbar nerve block can be performed using

2 ml of 2% lignocaine to inhibit the animal eye movement [20]. 2. Heat preservation After anesthesia, the mice were placed on a 37-degree thermostat animal table. 3. Pupil dilation 0.5% tropinamide or 1% atropine, start stimulation after 5 min of pupil dilation. 4. Cornea anesthesia 0.5% procaine. 5. The SLO stimulator The animal multifocal ERG needs a built-in SLO stimulator with multi-focus stimulation graphics and real-time monitoring of the position of the animal retina (Roland precision multifocal RETImap). 6 . Lens For multifocal ERG detection in mice, the special 60D mouse lens should be replaced in the SLO stimulator lens, and the human lens can be used for other animals. 7 . DTL electrode DTL electrode is generally used for precision multifocal ERG in mice. DTL fiber electrode with appropriate length is placed in the cornea of mice before examination. 8. Cornea contact lens Mouse precision multifocal ERG requires a 90D contact lens to be placed on the mouse cornea, as shown in Fig. 7.17.

7.4  Animal Examination SOP

Fig. 7.17  Cornea contact lens position for mouse mfERG

9.

10.

11.

12.

13.

Coupling agent Mice were first coated with 2% viscous methylcellulose gel on the lens, and then pressed on the corneas of mice with DTL electrodes. Connect the amplifier The DTL electrode is exposed on the outside of the lens and is clamped with the electrode rack as the active electrode to connect the red port of channel 1 of the amplifier. Electrodes The reference electrode was placed subcutaneously at the cheek on the side of the examination eye with a needle electrode, and the other segment was connected with the blue port of the amplifier 1 channel. The grounding electrode is set with needle electrode at the tail or hip subcutaneous, another segment is connected to the black port of the amplifier. Position The mice were placed in the front of the table with their eyes close to the center of the SLO stimulator lens and perpendicular to the lens. Fundus alignment To view the position of the mouse outer eye on the IR infrared laser real-time imaging window of the computer screen software of

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the SLO stimulator, and the mouse outer eye is moved in the center of IR window by moving the body of the SLO stimulator. The body of the SLO stimulator was gradually pushed to one side of the mouse by placing it in the center of the IR window. Meanwhile, the eyes of the mice were kept in the center of the IR window and gradually entered the mice fundus, gradually see the mouse fundus blood vessels, the SLO body can be moved up and down, left and right or oblique finetuning, and finally fine-tuning the IR SLO stimulator refraction compensation degree until the fundus image of the mouse was visible and cleaned, while the surrounding fundus visual field remained intact. The ideal eye position of mice is that the optic nerve head is in center of IR image, so it can be used as the multifocal ERG negative control point and anatomical indicator point to ensure the same anatomical site for each experiment. It can be adjusted by moving small mouse head position and SLO stimulator body tilt direction to achieve fundus position alignment. It takes practice to master as shown in Fig. 7.18. 14. Multifocal ERG stimulation In general, 19 hexagons were selected for multifocal ERG stimulation in mice, and the coefficient of variation was 1:1, that is, 19 hexagons had the same area. 1 5. Corneal protection Right panthenol protects the cornea after examination. 1 6. Other animals No special lens or contact lens is needed for the examination of rats and other large animals. Ring electrode or various contact lens electrodes can be selected, and the number of hexagons can be used, generally 37 or 61, coefficient of variation 1:1.

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Fig. 7.18  RETImap animal mfERG operation keys

7  Visual Electrophysiological in Animal Experiments

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