Refractive Surgery for High Myopia: Options and Special Considerations (Essentials in Ophthalmology) 3031405595, 9783031405594

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Essentials in Ophthalmology Series Editor: Arun D. Singh

J. Bradley Randleman   Editor

Refractive Surgery for High Myopia

Options and Special Considerations

Essentials in Ophthalmology Series Editor Arun D. Singh, Cleveland Clinic Foundation, Cole Eye Institute, Cleveland, OH, USA

Essentials in Ophthalmology aims to promote the rapid and efficient transfer of medical research into clinical practice. It is published in four volumes per year. Covering new developments and innovations in all fields of clinical ophthalmology, it provides the clinician with a review and summary of recent research and its implications for clinical practice. Each volume is focused on a clinically relevant topic and explains how research results impact diagnostics, treatment options and procedures as well as patient management. The reader-friendly volumes are highly structured with core messages, summaries, tables, diagrams and illustrations and are written by internationally well-known experts in the field. A volume editor supervises the authors in his/her field of expertise in order to ensure that each volume provides cuttingedge information most relevant and useful for clinical ophthalmologists. Contributions to the series are peer reviewed by an editorial board.

J. Bradley Randleman Editor

Refractive Surgery for High Myopia Options and Special Considerations

Editor J. Bradley Randleman Cole Eye Institute Cleveland Clinic Lerner College of Medic Cleveland, OH, USA

ISSN 1612-3212     ISSN 2196-890X (electronic) Essentials in Ophthalmology ISBN 978-3-031-40559-4    ISBN 978-3-031-40560-0 (eBook) https://doi.org/10.1007/978-3-031-40560-0 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

To the newest additions to my writing team, my beautiful twins Evan and Julia. May this be one of many adventures we share together!

Preface

A myopic epidemic is overtaking the globe, with dramatically increasing prevalence of myopia in general and high myopia in particular [1−3]. Regardless of the ultimate success of preventive measures, a significant portion of the world’s current population will reach adulthood with significant myopic refractive error. Fortunately, refractive surgery has seen tremendous progress in safety, efficacy, and treatment options over the last two decades. LASIK and photorefractive keratectomy (PRK) remain safe and effective options for the correction of high myopic refractive errors, while newer procedures including small incision lenticule extraction (SMILE), phakic intraocular lenses, and refractive lens exchange with new IOL technology have vastly expanded the spectrum of effective treatment options available. In the past decade alone, lenticule extraction approvals have expanded to treat high myopia with astigmatism, toric varieties of phakic intraocular lenses are now available, and a variety of presbyopia-correcting IOL technologies exist in both toric and non-toric models. Corneal cross-linking (CXL) has also become available worldwide and is evaluated as an adjunct procedure to stabilize corneas undergoing highly myopic corrections. Thus, the majority of highly myopia patients today can be treated with one or multiple effective procedures. The correction of high myopia is uniquely challenging, however, because significant safety concerns remain, and given the expanded treatment options there is frequently confusion regarding the best strategy for individual patients. There is thus a need for enhanced patient screening necessary to best match procedure with risk/benefit profile in this unique population. This book will endeavor to focus on the unique aspects of refracted surgical correction for high myopia to assist the reader in choosing the best procedures for each individual. Chapter 1 defines and details the problem facing our populations worldwide. Chapter 2 covers the basic tenets for refractive surgery screening and highlights the unique aspects critical for appropriate evaluation of the highly myopic patient. Chapters 3 through 7 discuss each available procedure in detail, including LASIK (Chap. 3), photorefractive keratectomy (Chap. 4), SMILE (Chapter 5), phakic IOLs (Chap. 6), and refractive lens exchange (Chap. 7). In Chap. 8, future considerations for the correction of high myopia are discussed, and in the final chapter the authors go through a series of real cases and discuss their thoughts, approaches, and treatment strategies, including when not to offer surgery.

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Preface

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Refractive surgery has come of age across a wide spectrum of refractive disorders and, with appropriate patient screening, presents a reasonable firstline solution to the growing problem of refractive errors in general and high myopia in particular. When considering all factors, refractive surgery may be the optimal option for the correction of refractive error in many instances [4, 5]. We hope you find this book enlightening on how to address the needs of your highly myopic patients most safely and efficaciously.

References 1. Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, et al. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology. 2016;123(5):1036-42. 2. Vitale S, Ellwein L, Cotch MF, Ferris FL, III, Sperduto R. Prevalence of Refractive Error in the United States, 1999-2004. Archives of Ophthalmology. 2008;126(8):1111-9. 3. Li Y, Liu J, Qi P.  The increasing prevalence of myopia in junior high school students in the Haidian District of Beijing, China: a 10-year population-based survey. BMC Ophthalmol. 2017;17(1):88. 4. Alió JL, Krueger RR, Bidgoli S.  The World Burden of Refractive Blindness. J Refract Surg. 2016 Aug 1;32(9):582-4. 5. Reinstein DZ. The Time Has Come for Refractive Surgery to Be Included in the Fight Against Global Visual Impairment Due to Uncorrected Refractive Error. J Refract Surg. 2022 Jan;38(1):6-8. Cleveland, OH, USA

J. Bradley Randleman

Contents

1 Epidemiology  of High Myopia����������������������������������������������������������  1 Ilyse D. Haberman 2 Preoperative  Evaluation for Refractive Surgery in Patients with High Myopia ����������������������������������������������������������  9 Lara Asroui and J. Bradley Randleman 3 LASIK  for High Myopia�������������������������������������������������������������������� 23 Gabriel S. Valerio and Edward E. Manche 4 PRK  for High Myopia������������������������������������������������������������������������ 31 Marcony R. Santhiago and Lycia Pedral Sampaio 5 SMILE  for High Myopia ������������������������������������������������������������������ 39 E. N. Wong and Jodhbir S. Mehta 6 Phakic  Intraocular Lens (pIOL) in the Treatment of High Myopia���������������������������������������������������������������������������������� 57 Majid Moshirfar, Amir Ali, Carter Payne, and Courtney Webster 7 Refractive  Lens Exchange in High Myopia ������������������������������������ 77 Julie M. Schallhorn 8 Future  Directions for High Myopia Correction������������������������������ 83 Sheetal Brar and Sri Ganesh 9 Refractive  Surgery for High Myopia: Case Section������������������������ 89 J. Bradley Randleman and Imane Tarib Index���������������������������������������������������������������������������������������������������������� 121

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Epidemiology of High Myopia Ilyse D. Haberman

Definition of Myopia Myopia is a refractive error within the eye that causes light to focus in front of the retina. This is usually caused by an increase in axial length, but also can be from increased corneal curvature or increased refractive power of the crystalline lens. The standard for measurement of refractive error is via cycloplegic refraction, especially in children. The World Health Organization defines myopia as refractive error less than or equal to −0.50D and high myopia as less than or equal to −5D. The International Myopia Institute, and most published studies, define high myopia as a refraction of −6D or more [1]. When interpreting prevalence rates in individual studies, it is important to note the refraction threshold for defining high myopia as well as whether the subjects were cyclopleged during refraction.

 revalence of Myopia and High P Myopia The prevalence of myopia varies across different regions of the world. Currently, 30–50% of American adults are myopic, and the rate rises to

as many as 90% in a population of East Asian school students [2, 3]. It is estimated that in the year 2000, there were 1.4 billion myopes (22.9% global prevalence) and 163 million people (2.7% global prevalence) with high myopia. Extrapolating current trends, by 2050 it is expected that 50% of the world’s population will be myopic, for a total of around 5 billion people. It is predicted that about 938 million people will have high myopia, or about 9.8% of the world’s population [2]. Figures  1.1 and 1.2 depict the relative proportion of refractive errors in the United States in 1999–2004, demonstrating the higher prevalence of myopia and high myopia among 20–39 year olds compared to those over 60 years [4]. The prevalence of myopia in school children has been studied and has demonstrated wide ranges across nations. Less developed nations often have a prevalence of less than 10% [5–7]. East Asia (including Singapore, urban areas of China, South Korea, and Taiwan) has the highest prevalence of myopia, reporting rates of anywhere from 29.5% to 90% of school-aged children [8–12]. France had a prevalence of 39.1% in 2013–2014 [13], and the United States similarly had a rate of 34.5% in 2010 [2].

I. D. Haberman (*) Department of Ophthalmology, NYU Langone Health, New York, NY, USA e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. B. Randleman (ed.), Refractive Surgery for High Myopia, Essentials in Ophthalmology, https://doi.org/10.1007/978-3-031-40560-0_1

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I. D. Haberman

I ncreasing Myopia Prevalence Worldwide

Fig. 1.1  Relative prevalence of refractive error in 20–39 year olds in the United States in 1999–2004 [4]

Fig. 1.2  Relative prevalence of refractive error in those over 60 years in the United States in 1999–2004 [4] Fig. 1.3  Increase in prevalence of myopia in 12–54 year olds in the United States from 1971–72 to 1999–2004 [14]

In addition to the high prevalence, it is important to recognize that the rates of myopia have been increasing over the last decades in many regions [1]. A study done in the United States noted an increase in all levels of myopia; it defined −2 to −7.9D as moderate myopia, and − 7.9D or more as high myopia. In 1971–1972, the prevalence of myopia in 12–54 year-olds overall was 25%, with moderate myopia comprising 11.4% and high myopia 0.2%. In 1999–2004, the overall prevalence of myopia increased to 41.6%, with both moderate and high myopia increasing to 22.4% and 1.6%, respectively (Fig. 1.3) [14]. Rates in children are notedly increasing over time. In Beijing, rates of myopia in 15 year olds increased from 55.95% in 2005 to 65.4% in 2015 [11]. In Fenghua, China, rates increased from 79.5% (2001) to 87.7% (2015) [15]. In Taiwan, prevalence of myopia at 12 years increased from 30.6% in 1983 to 76.67% by 2016 [16]. In the United States, prevalence has risen from 24% (1971–1972) to 33.9% (1999–2004) of 12–17 year olds (Fig. 1.4) [14]. The prevalence of high myopia has increased at a disproportionate rate; more myopes are becoming highly myopic. This may be due to the fact that children are becoming myopic earlier, allowing their myopia more time to progress [1, 17–21]. Children with diagnosis of myopia at

1  Epidemiology of High Myopia

3

Fig. 1.4  Increase in prevalence of myopia in children in the United States (1971–1972 to 1999–2004), Beijing China (2005–2015), Fenghua China (2001–2015), and Taiwann (1983–2016)

7–8 years had a higher risk of developing high myopia (53.9%) compared to those diagnosed at ages 9 (32.4%), 10 (19.4%), or older [20]. In Taiwan, the prevalence of high myopia in 15 year olds increased from 4.37% in 1983 to 15.36% in 2016 [16]. In a Finnish study, 32% of myopic children developed high myopia; the younger the diagnosis of myopia was made, the more likely they were to become high myopes [19].

 nvironmental Factors Contributing E to Myopia It is widely accepted that environmental factors play the biggest role in the increasing prevalence of myopia across many parts of the globe. Genetic factors, described in the next section, cannot explain the rapid change in myopia in recent decades, as the gene pool cannot change that fast [22]. Time outdoors, near-work, and education have been shown to be the strongest environmental risk factors (Table 1.1) [23–25]. As underdeveloped countries start to develop and institute more intensive educational systems, the prevalence of myopia is expected to grow [21]. Studies have shown that children that become myopic spend less time outdoors and that children who spend time outdoors are less likely to become myopic [23, 24, 27–29]. In a randomized trial, 40  minutes of outdoor school activities per day resulted in a decreased incidence of myopia from 39.5% to 30.4% [28]. Students in Taiwan random-

Table 1.1  Risk factors for myopia [26] Factors contributing to myopia Major factors:  Education  Nearwork  Time outdoors  Parental myopia Associated factors (potential confounders):  Increased socio-economic status (education)  Increased physical activity (time outdoors)  Higher intelligence (education)

ized to spend up to 11 hours outdoors weekly had less myopic shift and less axial elongation [29]. It has been shown that outdoor time can decrease the risk of myopia from increased near-work [30, 31]. The mechanism proposed in the benefit of outdoor time, which has been replicated in animal models, is that light stimulates release of retinal dopamine, which influences a retina-to-sclera signaling cascade and inhibits axial elongation [32]. Animal studies have demonstrated that brighter light produces more dopamine release from the retina, that dopamine slows axial elongation, and that bright light exposure can limit the development of experimental myopia [33, 34]. Increased education and near-work are also associated with the development of myopia [35, 16, 22]. Children who become myopic perform significantly more near-work than their non-­ myopic counterparts [23]. More time on near-­ work and less time outdoors correlated with the development of high myopia in a cohort of myo-

I. D. Haberman

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pic Finish students [19]. A study out of Taiwan showed that students attending extra classes for more than 2 hours per day had an increased risk of myopia [36]. The emphasis on education and competitive nature of the school systems in East Asia has been proposed as a causative factor in the high prevalence of myopia in the region. The quick generational change in prevalence of myopia has largely been attributed to education and to the emphasis placed on education in certain societies [37, 38]. In numerous studies, more educated people were found to be more myopic [16, 38, 39]. One such study demonstrated that Jewish boys in ultra-orthodox schools had a significantly higher prevalence of myopia (82.2%) and high myopia (27.6%) than boys in both orthodox schools (50.3% myopia and 7.1% high myopia) and secular schools (29.7% myopia and 2.0% high myopia) (39). This was thought to be due to imposed educational pressures on these students, emphasis on near-work, and less outdoor time, similar to trends seen in schools in East Asia.

identified that confer a higher risk for myopia [42]. Recognizing the genes involved in the development of myopia from these genome studies allowed researchers to further elucidate the underlying cells and pathways involved. Genes identified included those involved in corneal structure, lens shape, and development of cells of the retina, extracellular matrix, and vascular endothelium. Genes encoding for receptors and proteins involved in light processing pathways and dopamine regulation are identified, consistent with theories of light transduction as a mechanism for refractive error [32, 42]. Complex interactions between hundreds of candidate genes and the environment contributes to the development of myopia. It has been estimated that over 13,000 polymorphic variants are behind refractive error heritability, and that current published analyses only explain around 20% of its heritability [42, 52]. Future work with larger sample sizes will tell us more about the genes involved in the pathogenesis of myopia.

The Role of Genetics in Myopia

Syndromic Myopia

While the dramatic increase in prevalence of myopia is largely due to environmental factors [14, 40], it is known that there is a genetic predisposition to myopia [41, 42]. Parental myopia is significantly associated with myopia and high myopia in offspring [43, 44]. Familial clustering, twin, and offspring studies have demonstrated varying levels of heritability, from as low as 10% to as high as over 90% [42, 45–47]. Axial length and corneal curvature, two of the major determinants of myopia, have been shown to have high heritability [48, 49]. Linkage analysis in families with high myopia initially identified independent loci, MYP1–20, important in the development of high myopia, most on autosomal chromosomes [42, 44, 50, 51]. With the more recent advances in technology, large genome-wide association studies indicate that myopia is caused by a combination of many genes that contribute to overall risk. Through these methods, over 150 genetic loci have been

Secondary myopia is myopia that develops as the result of a syndrome. These forms of myopia are inherited as a result of a single gene mutation and display a variety of other clinical phenotypes. There are over 80 described genetic syndromes that feature myopia as one manifestation of the disease. The most commonly known are associated with connective tissue disorders, such as Marfan, Ehlers-Danlos, Stickler, and Weill-­ Marchesani syndromes [42]. Ocular syndromes associated with myopia include keratoconus, ocular albinism, ectopia lentis et pupillae, and Leber congenital amaurosis. Various inherited retinal dystrophies also commonly involve myopia, including cone dystrophy, cone-rod dystrophy, congenital stationary night blindness, and some forms of retinitis pigmentosa [42]. A comprehensive list of genetic syndromes associated with myopia can be found on the Online Mendelian Inheritance of Man website (https://www.omim.org).

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1  Epidemiology of High Myopia

Impact of Myopia

Summary

In 2020, undercorrected refractive error was the leading cause of moderate to severe visual impairment in the world and was the third most cause of global blindness (Table  1.2) [53]. Uncorrected myopic refractive error can lead to productivity losses, estimated at around $244 billion USD per year [54]. The cost to globally manage uncorrected myopia would be far below the world’s productivity losses [55]. In addition to monetary burdens, myopia significantly affects quality of life (QOL). Information derived from patient questionnaires show that people with higher magnitudes of myopia have poorer QOL [56]. Uncorrected refractive error affects patient-reported outcomes on ability to perform daily activities, economic well-­ being, and social well-being. Functional status was reduced in patients with high myopia, and individuals reported concern with cosmetic appearance and cost of lenses [1, 56]. Around 25% of patients with high myopia were reported to have depression and/or anxiety disorders [57]. QOL can be improved with the proper correction of myopia [58].

Myopia and high myopia are leading causes of visual impairment globally. The prevalence of each has been rising and is expected to continue to rise throughout the world. As children develop myopia earlier in life, they are more likely to become highly myopic, and the rates of high myopia are increasing disproportionally to the rates of myopia. It is, therefore, of great importance to recognize and correct this form of preventable vision impairment and blindness.

Table 1.2  Global causes of vision impairment and blindness in adults over 50 years [53] Moderate to severe vision impairment  Undercorrected refractive error (41%)  Cataract (38.9%)  Macular degeneration (3.0%)  Glaucoma (2.1%)  Diabetic retinopathy (1.4%) Blindness  Cataract (45.4%)  Glaucoma (11%)  Undercorrected refractive error (6.6%)  Macular degeneration (2.5%)  Diabetic retinopathy (2.5%)

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I. D. Haberman the risk of incident myopia. Invest Ophthalmol Vis Sci. 2017;58(2):1158–66. 25. Grzybowski A, Kanclerz P, Tsubota K, Lanca C, Saw SM.  A review on the epidemiology of myopia in school children worldwide. BMC Ophthalmol. 2020;20(1):27. 26. Morgan IG, Wu PC, Ostrin LA, Tideman JWL, Yam JC, Lan W, et al. IMI risk factors for myopia. Invest Ophthalmol Vis Sci. 2021;62(5):3. 27. Al-Mohtaseb Z, He X, Yesilirmak N, Waren D, Donaldson KE.  Comparison of corneal endothelial cell loss between two femtosecond laser platforms and standard phacoemulsification. J Refract Surg. 2017;33(10):708–12. 28. He M, Xiang F, Zeng Y, Mai J, Chen Q, Zhang J, et al. Effect of time spent outdoors at school on the development of myopia among children in China: a randomized clinical trial. JAMA. 2015;314(11):1142–8. 29. Wu PC, Chen CT, Lin KK, Sun CC, Kuo CN, Huang HM, et  al. Myopia prevention and outdoor light intensity in a school-based cluster randomized trial. Ophthalmology. 2018;125(8):1239–50. 30. Enthoven CA, Tideman JWL, Polling JR, Yang-Huang J, Raat H, Klaver CCW. The impact of computer use on myopia development in childhood: the generation R study. Prev Med. 2020;132:105988. 31. Rose KA, Morgan IG, Ip J, Kifley A, Huynh S, Smith W, et  al. Outdoor activity reduces the prevalence of myopia in children. Ophthalmology. 2008;115(8):1279–85. 32. Tedja MS, Wojciechowski R, Hysi PG, Eriksson N, Furlotte NA, Verhoeven VJM, et  al. Genome-wide association meta-analysis highlights light-induced signaling as a driver for refractive error. Nat Genet. 2018;50(6):834–48. 33. Ashby R, Ohlendorf A, Schaeffel F.  The effect of ambient illuminance on the development of deprivation myopia in chicks. Invest Ophthalmol Vis Sci. 2009;50(11):5348–54. 34. Cohen Y, Peleg E, Belkin M, Polat U, Solomon AS.  Ambient illuminance, retinal dopamine release and refractive development in chicks. Exp Eye Res. 2012;103:33–40. 35. Miraldi UV.  Nature versus nurture: a systematic approach to elucidate gene-environment interactions in the development of myopic refractive errors. Ophthalmic Genet. 2017;38(2):117–21. 36. Ku PW, Steptoe A, Lai YJ, Hu HY, Chu D, Yen YF, et al. The associations between near visual activity and incident myopia in children: a Nationwide 4-year follow-­up study. Ophthalmology. 2019;126(2):214–20. 37. Williams KM, Bertelsen G, Cumberland P, Wolfram C, Verhoeven VJ, Anastasopoulos E, et al. Increasing prevalence of myopia in Europe and the impact of education. Ophthalmology. 2015;122(7):1489–97. 38. Bez D, Megreli J, Bez M, Avramovich E, Barak A, Levine H.  Association between type of educational system and prevalence and severity of myopia among male adolescents in Israel. JAMA Ophthalmol. 2019;137(8):887–93.

1  Epidemiology of High Myopia 39. Morgan IG, French AN, Ashby RS, Guo X, Ding X, He M, et al. The epidemics of myopia: Aetiology and prevention. Prog Retin Eye Res. 2018;62:134–49. 40. Dolgin E.  The myopia boom. Nature. 2015;519(7543):276–8. 41. Dirani M, Chamberlain M, Shekar SN, Islam AF, Garoufalis P, Chen CY, et  al. Heritability of refractive error and ocular biometrics: the genes in myopia (GEM) twin study. Invest Ophthalmol Vis Sci. 2006;47(11):4756–61. 42. Tedja MS, Haarman AEG, Meester-Smoor MA, Kaprio J, Mackey DA, Guggenheim JA, et al. IMI myopia genetics report. Invest Ophthalmol Vis Sci. 2019;60(3):M89–M105. 43. Enthoven CA, Tideman JWL, Polling JR, Tedja MS, Raat H, Iglesias AI, et al. Interaction between lifestyle and genetic susceptibility in myopia: the generation R study. Eur J Epidemiol. 2019;34(8):777–84. 44. Baird PN, Schäche M, Dirani M. The GEnes in myopia (GEM) study in understanding the aetiology of refractive errors. Prog Retin Eye Res. 2010;29(6):520–42. 45. Young FA, Leary GA, Baldwin WR, West DC, Box RA, Harris E, et  al. The transmission of refractive errors within eskimo families. Am J Optom Arch Am Acad Optom. 1969;46(9):676–85. 46. Lopes MC, Andrew T, Carbonaro F, Spector TD, Hammond CJ.  Estimating heritability and shared environmental effects for refractive error in twin and family studies. Invest Ophthalmol Vis Sci. 2009;50(1):126–31. 47. Lyhne N, Sjølie AK, Kyvik KO, Green A. The importance of genes and environment for ocular refraction and its determiners: a population based study among 20-45 year old twins. Br J Ophthalmol. 2001;85(12):1470–6. 48. Kim MH, Zhao D, Kim W, Lim DH, Song YM, Guallar E, et  al. Heritability of myopia and ocular biometrics in Koreans: the healthy twin study. Invest Ophthalmol Vis Sci. 2013;54(5):3644–9. 49. Klein AP, Suktitipat B, Duggal P, Lee KE, Klein R, Bailey-Wilson JE, et al. Heritability analysis of spher-

7 ical equivalent, axial length, corneal curvature, and anterior chamber depth in the beaver dam eye study. Arch Ophthalmol. 2009;127(5):649–55. 50. Wojciechowski R.  Nature and nurture: the complex genetics of myopia and refractive error. Clin Genet. 2011;79(4):301–20. 51. Cai XB, Shen SR, Chen DF, Zhang Q, Jin ZB.  An overview of myopia genetics. Exp Eye Res. 2019;188:107778. 52. Hysi PG, Choquet H, Khawaja AP, Wojciechowski R, Tedja MS, Yin J, et  al. Meta-analysis of 542,934 subjects of European ancestry identifies new genes and mechanisms predisposing to refractive error and myopia. Nat Genet. 2020;52(4):401–7. 53. Collaborators GBaVI.  Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the right to sight: an analysis for the global burden of disease study. Lancet Glob Health. 2021;9(2):e144–e60. 54. Naidoo KS, Fricke TR, Frick KD, Jong M, Naduvilath TJ, Resnikoff S, et al. Potential lost productivity resulting from the global burden of myopia: systematic review, meta-analysis, and modeling. Ophthalmology. 2019;126(3):338–46. 55. Fricke TR, Holden BA, Wilson DA, Schlenther G, Naidoo KS, Resnikoff S, et al. Global cost of correcting vision impairment from uncorrected refractive error. Bull World Health Organ. 2012;90(10):728–38. 56. Rose K, Harper R, Tromans C, Waterman C, Goldberg D, Haggerty C, et al. Quality of life in myopia. Br J Ophthalmol. 2000;84(9):1031–4. 57. Yokoi T, Moriyama M, Hayashi K, Shimada N, Tomita M, Yamamoto N, et al. Predictive factors for comorbid psychiatric disorders and their impact on vision-related quality of life in patients with high myopia. Int Ophthalmol. 2014;34(2):171–83. 58. Lee J, Lee J, Park K, Cho W, Kim JY, Kang HY. Assessing the value of laser in situ keratomileusis by patient-reported outcomes using quality of life assessment. J Refract Surg. 2005;21(1):59–71.

2

Preoperative Evaluation for Refractive Surgery in Patients with High Myopia Lara Asroui and J. Bradley Randleman

There are numerous texts that cover the basic tenants of patient evaluation for refractive surgery. The basic contraindications for surgery apply to all patients (Table  2.1) [1–8]. The focus of this Table 2.1 General contraindications for laser vision correction Condition Absolute  Uncontrolled autoimmune diseases  Uncontrolled diabetes  Use of retinoic acid medications  Keratoconus  Corneal stromal dystrophies  Fuchs corneal dystrophy (for LASIK)  Pregnancy and active lactation  Severe dry eye Relative  Herpes simplex or herpes zoster  Glaucoma (severe or poorly controlled)  EBMD (for LASIK only)  Cataract (visually significant)  Residual stromal bed thickness 45

Minimum ECDACD ≥ 3.0 mm 3875 cells/mm2 3425 cells/mm2 3025 cells/mm2 2675 cells/mm2 2350 cells/mm2 2075 cells/mm2

Minimum ECDACD ≥ 3.2 mm 3800 cells/mm2 3375 cells/mm2 2975 cells/mm2 2625 cells/mm2 2325 cells/mm2 2050 cells/mm2

Minimum ECDACD ≥ 3.5 mm 3250 cells/mm2 2900 cells/mm2 2625 cells/mm2 2350 cells/mm2 2100 cells/mm2 1900 cells/mm2

Anterior Segment Evaluation

Pupils

Evaluating for evidence of mild anterior segment dysgenesis is important when considering PIOL implantation. Any lens opacity could be relevant for older patients desiring LVC or patients evaluated for PIOL implantation. A minimum anterior chamber depth (ACD) of 3.0  mm, or more depending on endothelial cell counts, is required for PIOL implantation (Table 2.2) [22]. Additional optical biometry measures such as axial length are needed for surgical planning of RLE and PIOL implantation.

Pupil size should be formally measured in room light and dim conditions. While pupil size has not been found to correlate with postoperative glare, halo, or night driving issues, generically termed night vision complaints (NVC), these measurements should be undertaken during LVC screening for all patients [26, 27]. Pupil size is directly relevant for PIOL screening, as the optical zone is fixed by IOL size, and patients with pupils larger than the IOL optic will experience increased symptoms in dim light [28].

Retinal Evaluation

Tear Film

Peripheral retinal evaluation is important for patients with high myopia. Even though neither LVC nor PIOL has been found to increase the risk of retinal detachment, these patients are at increased risk at baseline and significant peripheral retinal pathology should be ruled out before surgery [23, 24]. RLE is associated with an increased risk of retinal detachment, and a careful retinal evaluation is required for all patients undergoing the procedure [25]. Macular function evaluation with ocular coherence tomography has been advocated by many surgeons for presbyopia-correcting IOL evaluation.

There are multiple testing strategies for tear film evaluation, including vital dye staining, tear production testing (Schirmer’s), and tear break-up time, as well as newer tear osmolarity testing devices. Tear film should be evaluated in any patients with preoperative dry eye symptoms and in those individuals at greater risk for decreased tear production, including older patients and females. Tear film quality influences the choice of surgery as short-term postoperative dry eye symptoms are more significant after LASIK than SMILE [29]. Pretreatment may be advisable for certain patients, and patients with significant tear production issues should be excluded from LVC and may be better candidates for PIOL implantation.

Special Testing In addition to the aforementioned examinations, pupil size, tear film evaluation, and keratometry measurements should be obtained for high myopic refractive surgery candidates.

Keratometry Keratometry should be measured using manual or reliable automated devices. This information

12

is used for laser treatment programming for most ablations and may be important for planning flap creation if a mechanical microkeratome is utilized, as steep corneas (>48D) are at increased risk of buttonhole formation and flat corneas (20 degrees) with significant astigmatism   Asymmetric bowtie with skewed radial Axis (AB-SRAX)   Truncated bowtie   Vertical D   Drooping D   Pellucid marginal corneal degeneration (PMCD) aAgainst-the-rule steepening is not a definitively abnormal pattern, but in many instances subtle asymmetries in this orientation are missed; therefore, all cases with this pattern should be thoroughly evaluated

may still be variants of normal or only minimally concerning in patient screening if they exhibit mild asymmetry and/or occur with other findings that lessen their significance. As asymmetry increases, concern grows for a corneal ectatic process [51, 52]. Increasing asymmetry can manifest either as increased relative steepening in one meridian as compared to its opposite, as increasing deviation of the radial axis (called skewing or a skewed radial axis) (Fig. 2.5), or both, called an asymmetric bowtie with skewed radial axis (AB/ SRAX) pattern (Fig. 2.6). Small degrees of skew is typically not significant, while larger angles of skew represent clinically significant irregularity.

 etween Eye Asymmetry B Significant between eye asymmetry is an atypical finding in normal patients and warrants attention, even if neither pattern is absolutely abnormal unto itself. For the purposes of refractive surgical evaluation, the patient’s most suspicious topographic pattern between the two eyes should be given the most weight, as corneal ectasia is a bilateral disease process [55].

2  Preoperative Evaluation for Refractive Surgery in Patients with High Myopia

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Fig. 2.2  Scheimpflug refractive map image showing a truncated bowtie pattern in anterior curvature (upper left) with coincident focal anterior elevation (upper right).

Despite corneal pachymetry appearing normal (lower left), there is also a focal elevation on the posterior surface (lower right)

Fig. 2.3  Scheimpflug refractive map image showing a vertical D pattern in anterior curvature (upper left) with coincident focal anterior elevation that is shifted horizon-

tally (upper right) and a similarly located focal elevation on the posterior surface (lower right)

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L. Asroui and J. B. Randleman

Fig. 2.4  Scheimpflug refractive map image showing an against-the-rule steepening pattern in anterior curvature (upper left) with a significantly skewed axis with coincident focal anterior elevation that is shifted inferiorly (upper right)

Fig. 2.5  Scheimpflug refractive map image showing a skewed radial axis pattern with roughly 50 degrees of skew in anterior curvature (upper left) with coincident

focal anterior (upper right) and posterior (upper left) elevations that are shifted laterally

2  Preoperative Evaluation for Refractive Surgery in Patients with High Myopia

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Fig. 2.6  Scheimpflug refractive map image showing an asymmetric bowtie with skewed radial axis pattern in anterior curvature (upper left) with coincident focal anterior (upper right) and posterior (upper left) elevations

Corneal Elevation Corneal elevation maps are generated by comparing the corneal surface shape to a known reference shape, typically a best-fit sphere. Focal elevation in ectatic corneas is typically displaced inferiorly with respect to the corneal apex. Focal elevation is most concerning when it is co-located with other abnormalities of curvature and/or pachymetry, on their respective maps. Elevation maps are provided by most topography/tomography devices. Contrary to common dogma, elevation findings rarely present in the absence of asymmetric corneal curvature and should be considered supplementary in the screening process.

Regional Corneal Pachymetry In addition to thinner corneas indicating an increased risk of ectasia in terms of absolute thickness, the pattern of corneal pachymetry is similarly informative. Keratoconic corneas, including those with mild disease, have demonstrated a steep change, or rapid progression, of corneal thickness from the center of the cornea to

its periphery [56–58]. Several parameters and indices [58–61], available across different topographic and tomographic devices, have been developed based on these findings and are often used when screening patients for refractive surgery candidacy.

Epithelial Thickness Scheimpflug corneal tomography generates regional corneal thickness profiles along with anterior and posterior elevation maps. Scheimpflug tomography does not, however, provide sufficient resolution to evaluate epithelial thickness. Multiple anterior Segment Optical Coherence Tomography (AS-OCT) devices can now display total stromal and epithelial thickness maps across the central 6–9  mm (depending on the device). Epithelial thickness is also available using Highresolution very high-frequency digital ultrasound (VHFDU); however, although now commercially available, this technology is not widely in use clinically due to the challenges inherent in image acquisition, which requires a water bath in direct contact with the patient’s cornea.

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Fig. 2.7  Composite image showing two different epithelial thickness maps. In the left image, inferior epithelial hypertrophy would reduce the concern for a mildly asym-

metric curvature pattern, while the right image shows an epithelial map with focal thinning centrally which would increase concern for any curvature asymmetry

Subtle changes in epithelial thickness have significant implications for screening. Compensatory epithelial thinning overlying a focally steep region is an early sign of a corneal ectatic disorder (Fig. 2.7) [62–66]. Alternatively, many asymmetric steepening curvature patterns may be due to focal epithelial hypertrophy rather than indicative of an ectatic process (Fig.  2.7) [67]. Epithelial thickness maps may thus screen in as many patients if not more, than they screen out [68].

s­tiffness (resistance) and the ability to separate populations based on their output [69–73], to date neither device has proven more accurate than current morphologic measurements and therefore the clinical utility of these devices remains uncertain. A variety of metrics have been reported to interpret the findings from the Corvis; these include the Corvis Biomechanical Index (CBI) [74], which is derived specifically from the Corvis device, and the Tomographic Biomechanical Index (TBI) [75], which uses a combination of data acquired from the Corvis and the Pentacam devices. In clinical practice to date, the data derived from the Corvis is often equivocal and therefore of limited utility for patient screening.

Corneal Biomechanics Measurements All of the aforementioned techniques for evaluating corneal “biomechanical” integrity are in reality indirect measures, displaying corneal morphology rather than any direct biomechanical parameters. There has been great interest in the development of accurate corneal biomechanical measurement devices, but to date none have fulfilled the promise of actionable biomechanical data to confirm altered corneal integrity that precedes morphologic changes. Two devices have been in use clinically: the Ocular Response Analyzer (Reichert) and the Corvis ST (Oculus). While both devices have demonstrated the ability to measure some ocular properties of

Summary and Take Home Points Screening for refractive surgery factors in several elements which are important for any degree of myopic or hyperopic correction. For the correction of high myopia, particular attention is owed to certain components of the screening evaluation due to the higher ablation required to achieve the desired refractive outcome with LVC. Additional testing is also warranted when considering surgical options such as PIOL implantation and RLE,

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which are more commonly used for the correction of high myopia than any other refractive corrections.

20 J Ophthalmol. 1966;61(2):213–26. https://doi. org/10.1016/0002-­9394(66)90274-­1. 25. Colin J, Robinet A, Cochener B. Retinal detachment after clear lens extraction for high myopia: seven-year follow-up. Ophthalmology. 1999;106(12):2281–5. https://doi.org/10.1016/S0161-­6420(99)90526-­2. 26. Chan A, Manche EE.  Effect of preoperative pupil size on quality of vision after wavefront-guided LASIK.  Ophthalmology. 2011;118(4):736–41. https://doi.org/10.1016/j.ophtha.2010.07.030. 27. Schallhorn S, Brown M, Venter J, Hettinger K, Hannan S. The role of the mesopic pupil on patient-­ reported outcomes in young patients with myopia 1 month after wavefront-guided LASIK.  J Refract Surg. 2014;30(3):159–65. https://doi. org/10.3928/1081597X-­20140217-­02. 28. Lim DH, Lyu IJ, Choi SH, Chung ES, Chung TY. Risk factors associated with night vision disturbances after phakic intraocular lens implantation. Am J Ophthalmol. 2014;157(1):135–141.e1. https://doi. org/10.1016/j.ajo.2013.09.004. 29. Denoyer A, Landman E, Trinh L, Faure JF, Auclin F, Baudouin C.  Dry eye disease after refractive surgery: comparative outcomes of small incision lenticule extraction versus LASIK.  Ophthalmology. 2015;122(4):669–76. https://doi.org/10.1016/j. ophtha.2014.10.004. 30. Gimbel HV, Penno EE, van Westenbrugge JA, Ferensowicz M, Furlong MT. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology. 1998;105(10):1839–48. https:// doi.org/10.1016/s0161-­6420(98)91026-­0. 31. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115(1):37–50. https://doi.org/10.1016/j.ophtha.2007.03.073. 32. Randleman JB, Trattler WB, Stulting RD. Validation of the ectasia risk score system for preoperative laser in situ keratomileusis screening. Am J Ophthalmol. 2008;145(5):813–8. https://doi.org/10.1016/j. ajo.2007.12.033. 33. Krachmer JH, Feder RS, Belin MW. Keratoconus and related noninflammatory corneal thinning disorders. Surv Ophthalmol. 1984;28(4):293–322. https://doi. org/10.1016/0039-­6257(84)90094-­8. 34. Rabinowitz YS.  Keratoconus. Surv Ophthalmol. 1998;42(4):297–319. https://doi.org/10.1016/ s0039-­6257(97)00119-­7. 35. Roberts CJ, Dupps WJ Jr. Biomechanics of corneal ectasia and biomechanical treatments. J Cataract Refract Surg. 2014;40(6):991–8. https://doi. org/10.1016/j.jcrs.2014.04.013. 36. Randleman JB, Russell B, Ward MA, Thompson KP, Stulting RD. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology. 2003;110(2):267–75. https://doi.org/10.1016/S0161-­6420(02)01727-­X. 37. Saad A, Gatinel D.  Topographic and tomographic properties of forme fruste keratoconus corneas. Invest

L. Asroui and J. B. Randleman Ophthalmol Vis Sci. 2010;51(11):5546–55. https:// doi.org/10.1167/iovs.10-­5369. 38. Doughty MJ, Zaman ML.  Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol. 2000;44(5):367–408. https://doi.org/10.1016/ s0039-­6257(00)00110-­7. 39. Sedaghat MR, Daneshvar R, Kargozar A, Derakhshan A, Daraei M. Comparison of central corneal thickness measurement using ultrasonic pachymetry, rotating Scheimpflug camera, and scanning-slit topography. Am J Ophthalmol. 2010;150(6):780–9. https://doi. org/10.1016/j.ajo.2010.06.013. 40. Sorkin N, Kaiserman I, Domniz Y, Sela T, Munzer G, Varssano D.  Risk assessment for corneal ectasia following photorefractive keratectomy. J Ophthalmol. 2017;2017:2434830. https://doi. org/10.1155/2017/2434830. 41. Randleman JB, Dawson DG, Grossniklaus HE, McCarey BE, Edelhauser HF.  Depth-dependent cohesive tensile strength in human donor corneas: implications for refractive surgery. J Refract Surg. 2008;24(1):S85–9. https://doi. org/10.3928/1081597X-­20080101-­15. 42. Santhiago MR, Smadja D, Gomes BF, et  al. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol. 2014;158(1):87–95.e1. https://doi.org/10.1016/j. ajo.2014.04.002. 43. Santhiago MR, Wilson SE, Smadja D, Chamon W, Krueger RE, Randleman JB.  Validation of the percent tissue altered as a risk factor for ectasia after LASIK. Ophthalmology. 2019;126(6):908–9. https:// doi.org/10.1016/j.ophtha.2019.01.018. 44. Seiler T, Koufala K, Richter G.  Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg. 1998;14(3):312–7. https://doi. org/10.3928/1081-­597X-­19980501-­15. 45. Santhiago MR, Smajda D, Wilson SE, Randleman JB. Relative contribution of flap thickness and ablation depth to the percentage of tissue altered in ectasia after laser in situ keratomileusis. J Cataract Refract Surg. 2015;41(11):2493–500. 46. Santhiago MR, Smadja D, Wilson SE, Krueger RR, Monteiro ML, Randleman JB. Role of percent tissue altered on ectasia after LASIK in eyes with suspicious topography. J Refract Surg. 2015;31(4):258–65. 47. Randleman JB, Lynn MJ, Perez-Straziota CE, Weissman HM, Kim SW.  Comparison of central and peripheral corneal thickness measurements with scanning-slit, Scheimpflug and Fourier-domain ocular coherence tomography. Br J Ophthalmol. 2015;99(9):1176–81. 48. Randleman JB. Atlas of corneal imaging. Thorofare, NJ: SLACK Inc.; 2022. 49. Rabinowitz YS, McDonnell PJ.  Computer-assisted corneal topography in keratoconus. Refract Corneal Surg. 1989;5(6):400–8.

2  Preoperative Evaluation for Refractive Surgery in Patients with High Myopia 50. Wilson SE, Lin DT, Klyce SD. Corneal topography of keratoconus. Cornea. 1991;10(1):2–8. 51. Varssano D, Kaiserman I, Hazarbassanov R.  Topographic patterns in refractive surgery candidates. Cornea. 2004;23(6):602–7. https://doi. org/10.1097/01.ico.0000121699.74077.f0. 52. Rabinowitz YS, Yang H, Brickman Y, et  al. Videokeratography database of normal human corneas. Br J Ophthalmol. 1996;80(7):610–6. https://doi. org/10.1136/bjo.80.7.610. 53. Abad JC, Rubinfeld RS, Del Valle M, Belin MW, Kurstin JM. Vertical D: a novel topographic pattern in some keratoconus suspects. Ophthalmology. 2007;114(5):1020– 6. https://doi.org/10.1016/j.ophtha.2006.10.022. 54. Maguire LJ, Klyce SD, McDonald MB, Kaufman HE. Corneal topography of pellucid marginal degeneration. Ophthalmology. 1987;94(5):519–24. https:// doi.org/10.1016/s0161-­6420(87)33416-­5. 55. Gomes JAP, Tan D, Rapuano CJ, et  al. Global consensus on keratoconus and ectatic diseases. Cornea. 2015;34(4):359–69. https://doi.org/10.1097/ ICO.0000000000000408. 56. Gromacki SJ, Barr JT. Central and peripheral corneal thickness in keratoconus and normal patient groups. Optom Vis Sci. 1994;71(7):437–41. https://doi. org/10.1097/00006324-­199407000-­00003. 57. Pflugfelder SC, Liu Z, Feuer W, Verm A.  Corneal thickness indices discriminate between keratoconus and contact lens-induced corneal thinning. Ophthalmology. 2002;109(12):2336–41. https://doi. org/10.1016/s0161-­6420(02)01276-­9. 58. Avitabile T, Marano F, Uva MG, Reibaldi A. Evaluation of central and peripheral corneal thickness with ultrasound biomicroscopy in normal and keratoconic eyes. Cornea. 1997;16(6):639–44. 59. Avitabile T, Franco L, Ortisi E, et al. Keratoconus staging: a computer-assisted ultrabiomicroscopic method compared with videokeratographic analysis. Cornea. 2004;23(7):655–60. https://doi.org/10.1097/01. ico.0000127486.78424.6e. 60. Ambrósio R Jr, Caiado AL, Guerra FP, et  al. Novel pachymetric parameters based on corneal tomography for diagnosing keratoconus. J Refract Surg. 2011;27(10):753–8. https://doi. org/10.3928/1081597X-­20110721-­01. 61. Ambrósio R Jr, Alonso RS, Luz A, Coca Velarde LG.  Corneal-thickness spatial profile and corneal-­ volume distribution: tomographic indices to detect keratoconus. J Cataract Refract Surg. 2006;32(11):1851–9. https://doi.org/10.1016/j.jcrs.2006.06.025. 62. Reinstein DZ, Archer TJ, Gobbe M. Corneal epithelial thickness profile in the diagnosis of keratoconus. J Refract Surg. 2009;25(7):604–10. https://doi. org/10.3928/1081597X-­20090610. 63. Reinstein DZ, Gobbe M, Archer TJ, Silverman RH, Coleman DJ.  Epithelial, stromal, and total corneal thickness in keratoconus: three-dimensional display with Artemis very-high frequency digital ultrasound. J Refract Surg. 2010;26(4):259–71. https://doi. org/10.3928/1081597X-­20100218-­01.

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64. Rocha KM, Perez-Straziota CE, Stulting RD, Randleman JB.  SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes. J Refract Surg. 2013;29(3):173–9. https://doi. org/10.3928/1081597X-­20130129-­08. 65. Li Y, Chamberlain W, Tan O, Brass R, Weiss JL, Huang D.  Subclinical keratoconus detection by pattern analysis of corneal and epithelial thickness maps with optical coherence tomography. J Cataract Refract Surg. 2016;42(2):284–95. https://doi.org/10.1016/j. jcrs.2015.09.021. 66. Hwang ES, Schallhorn JM, Randleman JB. Utility of regional epithelial thickness measurements in corneal evaluations. Surv Ophthalmol. 2020;65(2):187–204. https://doi.org/10.1016/j.survophthal.2019.09.003. 67. Reinstein DZ, Archer TJ, Gobbe M.  Stability of LASIK in topographically suspect keratoconus confirmed non-keratoconic by Artemis VHF digital ultrasound epithelial thickness mapping: 1-year follow-up. J Refract Surg. 2009;25(7):569–77. https:// doi.org/10.3928/1081597X-­20090610-­02. 68. Asroui L, Dupps WJ Jr, Randleman JB. Determining the utility of epithelial thickness mapping in refractive surgery evaluations. Am J Ophthalmol. 2022;240:125– 34. https://doi.org/10.1016/j.ajo.2022.02.021. 69. Shah S, Laiquzzaman M, Bhojwani R, Mantry S, Cunliffe I. Assessment of the biomechanical properties of the cornea with the ocular response analyzer in normal and keratoconic eyes. Invest Ophthalmol Vis Sci. 2007;48(7):3026–31. https://doi.org/10.1167/ iovs.04-­0694. 70. Saad A, Lteif Y, Azan E, Gatinel D.  Biomechanical properties of keratoconus suspect eyes. Invest Ophthalmol Vis Sci. 2010;51(6):2912–6. https://doi. org/10.1167/iovs.09-­4304. 71. Luz A, Lopes B, Hallahan KM, et  al. Discriminant value of custom ocular response analyzer waveform derivatives in Forme Fruste keratoconus. Am J Ophthalmol. 2016;164:14–21. https://doi. org/10.1016/j.ajo.2015.12.020. 72. Sedaghat MR, Momeni-Moghaddam H, Ambrósio R Jr, et  al. Diagnostic ability of corneal shape and biomechanical parameters for detecting frank keratoconus. Cornea. 2018;37(8):1025–34. https://doi. org/10.1097/ICO.0000000000001639. 73. Koc M, Aydemir E, Tekin K, Inanc M, Kosekahya P, Kiziltoprak H.  Biomechanical analysis of subclinical keratoconus with Normal topographic, Topometric, and tomographic findings. J Refract Surg. 2019;35(4):247–52. https://doi. org/10.3928/1081597X-­20190226-­01. 74. Vinciguerra R, Ambrósio R, Elsheikh A, et  al. Detection of keratoconus with a new biomechanical index. J Refract Surg. 2016;32(12):803–10. https:// doi.org/10.3928/1081597X-­20160629-­01. 75. Ambrósio R, Lopes BT, Faria-Correia F, et  al. Integration of scheimpflug-based corneal tomography and biomechanical assessments for enhancing ectasia detection. J Refract Surg. 2017;33(7):434–43. https:// doi.org/10.3928/1081597X-­20170426-­02.

3

LASIK for High Myopia Gabriel S. Valerio and Edward E. Manche

Introduction High myopia can be defined as an axial length of 26 mm or greater. An alternate quantitative definition describes an optical system in which the spherical equivalent of the refractive error is −6.00 diopters or more. This is caused by an eye with an axial length that is longer than average or a cornea that is steeper than average, resulting in increased optical power [1]. Laser in situ keratomileusis (LASIK) has been shown to be a safe and effective method of correcting high myopia [2]. Despite many other alternate methods of correcting myopia including implantable collamer lenses, phakic intraocular lenses, and clear lens extraction, LASIK remains a primary method for treating high myopia [3]. LASIK has benefited from advancements in technology that have resulted in multiple excimer laser and femtosecond laser developments over the years. In eyes with very high myopia, the utility of LASIK has been extended to be used in combination with intraocular surgery, a method described as bioptics [4]. However, due to the nature of eyes with high myopia, complications such as ectasia, induction of higher order aberraG. S. Valerio Department of Ophthalmology, Naval Medical Center San Diego, San Diego, CA, USA E. E. Manche (*) Byers Eye Institute at Stanford University School of Medicine, Palo Alto, CA, USA

tions, residual refractive error, and potential vitreoretinal disruptions make treating high myopia unique when compared to treating lower refractive errors.

LASIK Technologies for High Myopia LASIK includes the creation of a corneal flap with either a manual keratome or a femtosecond laser. The stromal bed is then ablated with an excimer laser with which several technologies are available (Table  3.1). When treating high myopia, the creation of the flap should be taken into consideration. There are several options available including automated steel microkeratomes and advanced femtosecond lasers. Modern femtosecond lasers have become the preferred method as the flap thickness can be set to exact specifications for flap depth as well as creating flaps that are both planar and reverse beveled. These modifications are associated with more predictable results, less risks of complications, and improved clinical outcomes [5]. In patients with high myopia, thin-flap LASIK (100 μm flaps or thinner) may allow higher treatments to be performed while reducing the risk of ectasia by maximizing the residual stromal bed and biomechanical stability of the cornea [6]. Conventional LASIK is based on Munnerlyn’s equation which determines the amount of

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. B. Randleman (ed.), Refractive Surgery for High Myopia, Essentials in Ophthalmology, https://doi.org/10.1007/978-3-031-40560-0_3

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24 Table 3.1  Upper limits of myopia treatments for excimer lasers approved by the U.S. FDA Upper limits myopia treatments for excimer lasers approved by the U.S. FDA VISX Star S4 IR Excimer Laser System Conventional Up to −14.0 DS with or without LASIK astigmatism −0.5 to −5.0 diopters cylinder CustomVue WFG Up to −11.0 D MRSE, with or LASIK (WaveScan without astigmatism up to −3.0 Wavefront System) diopters cylinder iDesign WFG Up to −11.0 DS with or without LASIK (iDesign astigmatism up to −5.0 diopters Wavefront System) cylinder Alcon Wavelight EX500 Excimer Laser System WFO LASIK Up to −12.0 D with or without astigmatism of up to −6.0 diopters of cylinder WFG LASIK Up to −7.0 D with up to −3.0 D (Wavelight Allegro of astigmatism and with Analyzer) manifest refractive spherical equivalent of up to −7.0 D Topography-Guided Up to −9.0 of SE myopia or with LASIK astigmatism, with up to −8.0 D of spherical component and up to −3.0 D of astigmatic component NIDEK EC-5000 Excimer Laser System Topography-assisted Up to −5.0 D of sphere with LASIK astigmatic refractive errors from > − 0.5 to −2.0 D with MRSE of > − 1.0D to −6.0 D CARL ZEISS MEDITEC MEL-80 Excimer Laser System LASIK Up to – 7.0 D with or without refractive astigmatism of less than or equal to −3.0 D, with a maximum of MRSE of −7.0 D

c­ orneal tissue that is to be removed to flatten the cornea and treat refractive error. A conventional LASIK ablation has a minimal blend zone outside of the prescribed base treatment. Early conventional treatments were associated with the induction of positive spherical aberrations which were highly correlated with higher myopic corrections. Modern laser technology including wavefront-­guided (WFG) LASIK and wavefront-optimized (WFO) LASIK have been shown to have a high level of efficacy in treating high myopia while reducing the induction of higher-order aberrations when compared to conventional LASIK.

G. S. Valerio and E. E. Manche

Wavefront-guided (WFG) LASIK is an excimer laser technology used to ablate the cornea in a sophisticated pattern that is based on the patient’s individual aberrometry. Thus, in addition to the spherical and cylindrical lower order aberrations, WFG LASIK attempts to treat higher-order aberrations as measured by the aberrometer. In general, WFG LASIK is considered superior to conventional LASIK.  In a premarket approval study of 1015 eyes, 84.1% to 93.9% of eyes achieved 20/20 or better UCVA at postoperative month six [7]. Regarding higher myopic corrections, a multicenter study evaluated a WFG platform assessing a group of eyes with a mean preoperative manifest refraction spherical equivalent (MRSE) of −8.5 diopters (range −6.4D to −11.8 diopters) and found that 84% of eyes were 20/20 or better [8]. Wavefront-optimized (WFO) LASIK is another modern excimer laser technology that uses optimized peripheral corneal treatment profiles that are population based. It allows for correction of spherical and cylindrical refractive errors while preserving the natural aspheric shape of the cornea which neutralizes the laser-induced spherical aberrations previously associated with conventional LASIK treatments. WFO LASIK in patients with very high myopia (−10.0 to −13.50 D) was found to have an efficacy index (which is determined by uncorrected visual acuity (UCVA) and manifest refraction spherical equivalent (MRSE) of 0.93 ± 0.20, resulting in excellent visual outcomes and high patient satisfaction [9].

LASIK Outcomes in High Myopia Outcomes of LASIK in high myopia have improved significantly as technology has advanced. With earlier excimer laser technologies, treatment of extreme amounts of myopia were associated with poor visual outcomes, low predictability, and significant regression [2]. Recent literature suggests that LASIK treatment of high myopia now has excellent outcomes with excellent safety and efficacy. Large reports of LASIK in high myopes like that of Yuen et al. [10] and Vega-Estrada et  al. [11] found that 10- and 5-year follow-ups, respectively, resulted in stable

3  LASIK for High Myopia

visual, refractive, and aberrometry outcomes when modern lasers and technology are utilized. A report by Artini et al. [12] found that modern LASIK technologies that utilize fast repetition, small scanning laser spots, optimized ablation profile, larger optical zones, and faster eye tracking, result in achieving treatment targets (spherical equivalent correction ±0.5 diopters in attempted versus achieved) in 96.1% of patients with high myopia (−6.01 to −9.0 diopters) and 69.9% of patients with very high ­myopia (−9.01 or higher). Other excimer platforms have found similar high efficacy and safety for the treatment of high myopia to include up to −14.25 D [13]. Results comparing low myopic treatments and high myopic treatments vary in the literature. Although in general safety and efficacy are excellent in high myopia, studies have shown less predictability in these same high myope groups [14, 15]. Undercorrection is the most common complication when assessing attempted correction versus achieved in these populations. Nomogram adjustment of excimer treatments in high myopes may result in less undercorrection and further improved outcomes [2].

 ASIK Compared to Other Forms L of Refractive Surgery High myopia can be treated with several surgical methods. Photorefractive keratectomy (PRK) has been compared to LASIK in this group of patients. When comparing treatment groups of high myopia between photorefractive keratectomy (PRK) and LASIK, LASIK resulted in superior efficacy and stability while showing similar outcomes in safety [3, 16, 17]. For example, a study that followed patients out to 18 months postoperatively showed that 75% of LASIK patients versus 57.1% of PRK patients had 20/20 uncorrected visual acuity [17]. In regards to regression, mean myopic regression in high myopes is reported to be less in LASIK than in PRK [18]. One study reported a mean myopic regression of 1.30 D in PRK while the same matched group was noted to result in only 0.92 D in the high myopia LASIK group [19]. Another

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disadvantage of PRK in high myopes, that is not seen in LASIK patients, is the development of postoperative haze which is more common in higher treatments [20]. Another common method of surgical correction for high myopia includes the implantation of phakic intraocular lenses, especially in patients with 7.0 diopters of myopia or more. Other than very high myopia, this technology is indicated in patients with very thin corneas or those with abnormal corneal topography that may place patients at risk of corneal ectasia. A Cochrane review that evaluated three randomized controlled trials, totaling 228 eyes treated, compared phakic intraocular lenses to excimer laser refractive surgery in high myopes (−6.0 to −20.0 D). The study found that the percentage of eyes with uncorrected visual acuity of 20/20 or better was not statistically different at 12 months postoperatively. The same review noted that phakic IOL surgery resulted in a higher safety profile as there was less final loss of best-corrected visual acuity [21]. Phakic IOL surgery remains a valid option in the treatment of high myopia as patients displayed better contrast sensitivity and reported higher patient satisfaction surveys compared to LASIK. Apparent limitations in phakic IOL surgery include the level of surgical complexity and skill required to perform the surgery safely. Small incision lenticule extraction (SMILE) is another corneal refractive surgery that has been gaining popularity in the United States and worldwide. SMILE differs from LASIK in that there is no use of an excimer laser and only a femtosecond laser is used to remove a lenticule of tissue resulting in a flapless corneal refractive procedure. When comparing wavefront-guided LASIK with early SMILE technology, both procedures offered excellent predictability with WFG LASIK resulting in faster visual recovery, better low-contrast visual acuity, and greater gains in uncorrected visual acuity [22]. As SMILE is the newest technology of modern refractive surgery lasers, there remains a paucity of literature when comparing these two technologies for the correction of high myopia. Current literature supports that both SMILE and LASIK surgery for the correction of myopia provides

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excellent outcomes [23]. Optical quality was shown to be decreased for both SMILE and LASIK in these high myopic treatment groups [24]. However, subjective visual symptoms as measured by Quality of Vision scores are comparable between the two groups [25].

High Myopia LASIK Complications Performing LASIK to treat high myopia can be associated with a number of complications including under or overcorrection, corneal ectasia, induction of higher-order aberrations and the potential for vitreoretinal disruptions.

Undercorrection The most common complication following LASIK for high myopia is undercorrection. This may be due to inadequate ablation, wound healing, or epithelial hyperplasia [26, 27]. Myopic regression with conventional LASIK has been attributed to corneal steepening that occurred over a 12-year observation period by Ikeda et al. [28]. In this study, at postoperative year 12, 53% and 75% of the eyes were within 0.5 and 1.0 D, respectively, of the targeted correction. Older data suggested regression of the mean refractive change to be −0.5 D over 5  years, but when severely myopic eyes were isolated the regression of the mean refractive change was found to be −1.06 D [29]. Another paper by Alio et  al. found the mean myopic regression in patients with myopia exceeding −10 diopters to be −0.52 D per year [30]. In addition, Rosman et  al. who also looked at LASIK in myopia exceeding −10.0 diopters found that after 10 years of follow-up, only 45.5% had a UCVA of 20/40 or better, and that the safety index was 0.87 [31]. Despite new excimer and femtosecond laser technologies, regression appears to be similar to older data with overall refractive predictabilities decreasing significantly over time [32]. In general, patients who experience postoperative refractive error and associated reduced uncorrected distance visual acuity are more

G. S. Valerio and E. E. Manche

likely to report dissatisfaction with the outcomes of their refractive procedure [7].

Postoperative Ectasia Post-LASIK ectasia is a rare but concerning complication. It is defined as the development of increasing myopia, with or without increasing astigmatism, loss of uncorrected visual acuity with focal anterior curvature steepening, with or without central and paracentral corneal thinning, and topographic evidence of asymmetric inferior corneal steepening after LASIK [33]. This occurs after LASIK surgery as the cornea is permanently and structurally altered by both the laser ablation as well as the creation of the flap. A study of 2873 eyes by Pallikaris showed that 19 eyes (0.66%) had developed post-LASIK ectasia [34]. Interestingly, in the patients that had developed ectasia, it was noted that they were treated for 8.0 diopters of myopia or greater and had residual stromal beds that were less than 325 μm. Post-LASIK ectasia is often associated with a lower residual stromal bed which is often the case in treating high myopia in LASIK. Although 250–300 μm of residual stromal bed is customary and generally recognized as a minimum for LASIK, there is no scientific evidence to strongly support this as a strict cutoff. Santhiago and colleagues introduced the concept of percent tissue ablated (PTA) in LASIK surgery [35]. Percent tissue ablated (PTA) defined as the tissue altered (including LASIK flap and ablated tissue) as a percent of the entire corneal thickness, greater than 40% has also been described to be associated with the development of ectasia after LASIK surgery [35]. Randleman and colleagues introduced the ectasia risk score system to help evaluate patients’ eyes preoperatively for the risk of developing ectasia postoperatively following LASIK surgery [36, 37]. The risk factors for ectasia identified based on retrospective analysis included (1) abnormal preoperative topography, (2) low residual bed thickness, (3) young age, (4) low preoperative corneal thickness, and (5) high myopia [36, 37]. This suggests that meticulous preoperative patient selection is necessary to reduce the risk of postoperative ectasia.

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HOA Induction

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low-­up study of 38,823 cases that revealed the rate of retinal detachment was 0.08% [41]. Increased higher-order aberrations (HOAs) have Regardless, it is imperative that patients with been associated with higher LASIK treatments high myopia that are being considered for LASIK and are described as adverse visual phenomena, surgery have a full preoperative exam and postsuch as halos, glare, and starbursts. A study using operative exams to evaluate for lattice degeneraconventional LASIK in 2005 showed that higher-­ tion, retinal holes and other retinal lesions that order aberrations were induced and significantly may predispose patients to retinal detachments. associated with increasing refractive corrections; especially in myopic treatments 6.0 diopters and higher, and hyperopic treatments 5.0 diopters and LASIK Combined with Other higher [38]. High myopia LASIK treatments Procedures to Treat High Myopia most commonly increase the HOAs: coma and spherical aberration (Fig.  3.1). Larger ablation For patients with high myopia, correction of their depths are associated with larger influences on refractive error may be limited by the upper limthese adverse visual phenomena [39, 40]. its of excimer laser technology or residual stromal bed thickness, that may put them at risk for post-LASIK ectasia. For these patients, one can Retinal Detachment consider bioptics, which is a surgical technique first described by Zaldivar et al. [42]. In this techHigh myopia is an independent risk factor for nique, a phakic intraocular lens is used to treat retinal detachment. Despite some early concern the majority of the refractive error and corneal for the theoretical risk of increased occurrence of refractive surgery may be used to treat residual retinal detachment after treating high myopia refractive error, leading to less tissue ablated, less (due to disruption of the anterior retina during chance of higher-order aberrations, less chance suction applied for the femtosecond laser flap of regression, and increased accuracy in final creation), no direct correlation has been identi- visual outcomes. Several studies have revealed fied. This has been confirmed in a long-term fol- that 80% of patients were within 0.5 diopters and Fig. 3.1  Diagram of spherical aberration. Top. A perfect optical system will result in a single focal point. Bottom. An imperfect optical system with spherical aberration where the different rays of light do not meet in one focal point

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all patients were within 1.0 diopters of the intended treatment with the bioptics technique [43–45]. See Chap. 6 for more information on phakic IOLs. LASIK may also be considered as a follow-up procedure for high myopic patients that undergo refractive lens exchange (also termed clear lens extraction) or cataract surgery. When treating residual refractive error, either as a planned staged approach or as an enhancement after intraocular surgery, it is advisable to perform LASIK only after refractive stability has been achieved, which is usually confirmed 3 months after the initial clear lens extraction. Modern intraocular lenses that utilize either monofocal or multifocal technology, combined with LASIK surgery provide excellent visual outcomes [46, 47]. It is important to note and emphasize the risks of intraocular surgery including retinal detachment, macular edema, and endothelial cell loss for patients that are being considered for a bioptics surgical procedure. See Chap. 7 for more information on refractive lens exchange.

Disclaimer The view expressed in this chapter are those of the author and do not necessarily reflect the official policy or position of the Department of the Navy, or the Department of Defense, nor the US Government. No financial interests to disclose. Financial Disclosures  E.M. is a consultant for Avedro, Carl Zeiss Meditec, Evommune, and Johnson & Johnson Vision Surgical; has received research support from Allergan, Alcon, Avedro, Carl Zeiss Meditec, Johnson & Johnson Vision, and Novartis; holds equity in RxSight, Placid0, and VacuSite; and holds patents assigned to VacuSite.

References 1. Flitcroft DI, He M, Jonas JB, Jong M, Naidoo K, Ohno-Matsui K, et al. IMI – defining and classifying myopia: A proposed set of standards for clinical and epidemiologic studies. Investig Opthalmol Vis Sci. 2019;60(3):M20.

G. S. Valerio and E. E. Manche 2. Schallhorn SC, Venter JA, Hannan SJ, Hettinger KA. Outcomes of wavefront-guided laser in situ keratomileusis using a new-generation Hartmann-shack aberrometer in patients with high myopia. J Cataract Refract Surg. 2015;41(9):1810–9. 3. Ang EK, Couper T, Dirani M, Vajpayee RB, Baird PN. Outcomes of laser refractive surgery for myopia. J Cataract Refract Surg. 2009;35(5):921–33. 4. Bleckmann H, Jørgensen J, Lamcke I, Keuch R. Bioptic. A refractive surgery procedure for correction of high and extreme myopia. Ophthalmol Z Dtsch Ophthalmol Ges. 2002;99(12):936–40. 5. Ozulken K, Yuksel E, Tekin K, Kiziltoprak H, Aydogan S.  Comparison of Wavefront-Optimized Ablation and Topography-Guided Contoura Ablation with LYRA Protocol in LASIK.  J Refract Surg Thorofare NJ 1995. 2019;35(4):222–9. 6. Durrie DS, Slade SG, Marshall J.  Wavefront-guided excimer laser ablation using photorefractive keratectomy and sub-Bowman’s keratomileusis: a contralateral eye study. J Refract Surg Thorofare NJ 1995. 2008;24(1):S77–84. 7. Schallhorn SC, Farjo AA, Huang D, Boxer Wachler BS, Trattler WB, Tanzer DJ, et al. Wavefront-guided LASIK for the correction of primary myopia and astigmatism a report by the American Academy of ophthalmology. Ophthalmology. 2008;115(7):1249–61. 8. Duker MD JS, Yanoff MD M [Editor. Ophthalmology: Expert Consult: Online and Print [Internet]. Usa: Mosby; 2008 [cited 2022 Jun 20]. Available from: https://www.biblio.com/book/ophthalmology-­expert-­ consult-­online-­print-­duker/d/1474295558 9. Wallerstein A, Gauvin M, Cohen M.  WaveLight® Contoura topography-guided planning: contribution of anterior corneal higher-order aberrations and posterior corneal astigmatism to manifest refractive astigmatism. Clin Ophthalmol Auckl NZ. 2018;12:1423–6. 10. Yuen LH, Chan WK, Koh J, Mehta JS, Tan DT, Sing Lasik Research Group. A 10-year prospective audit of LASIK outcomes for myopia in 37,932 eyes at a single institution in Asia. Ophthalmology. 2010;117(6):1236–1244.e1. 11. Vega-Estrada A, Alio JL. Femtosecond-assisted laser in situ keratomileusis for high myopia correction: long-term follow-up outcomes. Eur J Ophthalmol. 2020;30(3):446–54. 12. Artini W, Riyanto SB, Hutauruk JA, Gondhowiardjo TD, Kekalih A.  Predictive factors for successful high myopia treatment using high-frequency laser-in-situ Keratomileusis. Open Ophthalmol J. 2018;12(1):214–25. 13. Reinstein DZ, Carp GI, Archer TJ, et  al. Long-term visual and refractive outcomes after lasik for high myopia and astigmatism from −8. 00 to −14. 25 d. J Refract Surg. 2016;32(5):290–7. Long-term Visual and Refractive Outcomes After LASIK for High Myopia and Astigmatism From −8.00 to −14.25 D | Journal of Refractive Surgery [Internet]. [cited 2022 May 22]. Available from: https://journals.healio.com/ doi/epdf/10.3928/1081597X-­20160310-­01

3  LASIK for High Myopia 14. Kojima T, Hallak JA, Azar DT. Control-matched analysis of laser in situ keratomileusis outcomes in high myopia. J Cataract Refract Surg. 2008;34(4):544–50. 15. Niparugs M, Tananuvat N, Chaidaroon W, Tangmonkongvoragul C, Ausayakhun S.  Outcomes of LASIK for myopia or myopic astigmatism correction with the FS200 femtosecond laser and EX500 excimer laser platform. Open Ophthalmol J. 2018;12(1):63–71. 16. Dirani M, Couper T, Yau J, Ang EK, Islam AFM, Snibson GR, et  al. Long-term refractive outcomes and stability after excimer laser surgery for myopia. J Cataract Refract Surg. 2010;36(10):1709–17. 17. Hashemi H, Ghaffari R, Miraftab M, Asgari S. Femtosecond laser-assisted LASIK versus PRK for high myopia: comparison of 18-month visual acuity and quality. Int Ophthalmol. 2017;37(4):995–1001. 18. Amano S, Shimizu K. Excimer laser photorefractive keratectomy for myopia: two-year follow up. J Refract Surg Thorofare NJ 1995. 1995;11(3 Suppl):S253–60. 19. Helmy SA, Salah A, Badawy TT, Sidky AN.  Photorefractive keratectomy and laser in situ keratomileusis for myopia between 6.00 and 10.00 diopters. J Refract Surg Thorofare NJ 1995. 1996;12(3):417–21. 20. Rosman M, Alió JL, Ortiz D, Perez-Santonja JJ.  Comparison of LASIK and photorefractive keratectomy for myopia from −10.00 to −18.00 diopters 10 years after surgery. J Refract Surg. 2010;26(3):168–76. 21. Barsam A, Allan BD. Excimer laser refractive surgery versus phakic intraocular lenses for the correction of moderate to high myopia. Cochrane Eyes and Vision Group, editor. Cochrane Database Syst Rev [Internet]. 2014 Jun 17 [cited 2022 May 22]; Available from: https://doi.wiley.com/10.1002/14651858.CD007679. pub4 22. Chiang B, Valerio GS, Manche EE.  Prospective, randomized, contralateral eye comparison of Wavefront-guided laser in situ Keratomileusis (WFG-LASIK) and small incision Lenticule extraction (SMILE) refractive surgeries. Am J Ophthalmol. 2021;S0002-9394(21):00596–1. 23. Qian Y, Chen X, Naidu RK, Zhou X.  Comparison of efficacy and visual outcomes after SMILE and FS-LASIK for the correction of high myopia with the sum of myopia and astigmatism from −10.00 to −14.00 dioptres. Acta Ophthalmol. 2020;98(2):e161–72. 24. Yin Y, Lu Y, Xiang A, Fu Y, Zhao Y, Li Y, et  al. Comparison of the optical quality after SMILE and FS-LASIK for high myopia by OQAS and iTrace analyzer: a one-year retrospective study. BMC Ophthalmol. 2021;21(1):292. 25. He S, Luo Y, Chen P, Ye Y, Zheng H, Lan M, et  al. Prospective, randomized, contralateral eye comparison of functional optical zone, and visual quality after SMILE and FS-LASIK for high myopia. Transl Vis Sci Technol. 2022;11(2):13.

29 26. Lohmann CP, Güell JL. Regression after LASIK for the treatment of myopia: the role of the corneal epithelium. Semin Ophthalmol. 1998;13(2):79–82. 27. Pérez-Santonja JJ, Ayala MJ, Sakla HF, Ruíz-Moreno JM, Alió JL. Retreatment after laser in situ keratomileusis. Ophthalmology. 1999;106(1):21–8. 28. Ikeda T, Shimizu K, Igarashi A, Kasahara S, Kamiya K.  Twelve-year follow-up of laser in situ Keratomileusis for moderate to high myopia. Biomed Res Int. 2017;2017:1–7. 29. O’Doherty M. Five year follow up of laser in situ keratomileusis for all levels of myopia. Br J Ophthalmol. 2006;90(1):20–3. 30. Alió JL, Muftuoglu O, Ortiz D, Pérez-Santonja JJ, Artola A, Ayala MJ, et  al. Ten-year follow-up of laser in situ keratomileusis for high myopia. Am J Ophthalmol. 2008;145(1):55–64. 31. Rosman M, Alió JL, Ortiz D, Pérez-Santonja JJ. Refractive stability of LASIK with the Visx 20/20 excimer laser vs ZB5m phakic iol implantation in patients with high myopia (>−10.00 d): a 10-year retrospective study. J Refract Surg Thorofare NJ 1995. 2011;27(4):279–86. 32. Kim JY, Lee H, Joo CK, Hyon JY, Kim TI, Kim JH, et al. Three-year follow-up of laser in situ Keratomileusis treatments for myopia: multi-center cohort study in Korean population. J Pers Med. 2021;11(5):419. 33. Binder PS, Lindstrom RL, Stulting RD, Donnenfeld E, Wu H, McDonnell P, et  al. Keratoconus and corneal ectasia after LASIK. J Refract Surg Thorofare NJ 1995. 2005;21(6):749–52. 34. Pallikaris IG, Kymionis GD, Astyrakakis NI. Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg. 2001;27(11):1796–802. 35. Santhiago MR, Smadja D, Gomes BF, Mello GR, Monteiro MLR, Wilson SE, et al. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol. 2014;158(1):87–95.e1. 36. Randleman JB, Trattler WB, Stulting RD. Validation of the ectasia risk score system for preoperative laser in situ keratomileusis screening. Am J Ophthalmol. 2008 May;145(5):813–8. 37. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115(1):37–50. 38. Pesudovs K.  Wavefront aberration outcomes of LASIK for high myopia and high hyperopia. J Refract Surg [Internet]. 2005 Sep 2 [cited 2022 May 22];21(5). Available from: https://journals.healio. com/doi/10.3928/1081-­597X-­20050901-­18 39. Feng Z, Wang Q, Du C, Yang F, Li X.  High-order aberration changes after femtosecond LASIK surgery in patients with high myopia. Ann Palliat Med. 2021;10(7):7689–96. 40. Moreno-Barriuso E, Lloves JM, Marcos S, Navarro R, Llorente L, Barbero S. Ocular Aberrations before and after Myopic Corneal Refractive Surgery: LASIK-­

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Induced Changes Measured with Laser Ray Tracing. fixated phakic intraocular lenses. Ophthalmol J Investig Ophthalmol Visual Sci. 2001;42(6):8. Int Ophtalmol Int J Ophthalmol Z Augenheilkd, 2. 41. Lin J, Xie X, Du X, Yang Y, Yao K. Incidence of vit2008;222:69–73. reoretinal pathologic conditions in myopic eyes after 45. Muñoz G, Alió JL, Montés-Micó R, Belda JI. Angle-­ laser in situ keratomileusis. Zhonghua Yan Ke Za Zhi supported phakic intraocular lenses followed by laser-­ Chin J Ophthalmol. 2002;38(9):546–9. assisted in situ keratomileusis for the correction of 42. Zaldivar R, Davidorf JM, Oscherow S, Ricur G, high myopia. Am J Ophthalmol. 2003;136(3):490–9. Piezzi V. Combined posterior chamber phakic intraoc- 46. Piñero DR, Ayala Espinosa MJ, Alió JL.  LASIK ular lens and laser in situ keratomileusis: bioptics for outcomes following multifocal and monofocal intraextreme myopia. J Refract Surg Thorofare NJ 1995. ocular lens implantation. J Refract Surg Thorofare NJ 1999;15(3):299–308. 1995. 2010;26(8):569–77. 43. Güell JL, Vázquez M, Gris O.  Adjustable refrac- 47. Muftuoglu O, Prasher P, Chu C, Mootha VV, Verity tive surgery: 6-mm artisan lens plus laser in situ SM, Cavanagh HD, et al. Laser in situ keratomileusis keratomileusis for the correction of high myopia. for residual refractive errors after apodized diffractive Ophthalmology. 2001;108(5):945–52. multifocal intraocular lens implantation. J Cataract 44. Meltendorf C, Cichocki M, Kohnen T.  Laser in situ Refract Surg. 2009;35(6):1063–71. keratomileusis following the implantation of iris-­

4

PRK for High Myopia Marcony R. Santhiago and Lycia Pedral Sampaio

Photorefractive Keratectomy in Eyes with High Myopia The definitions of high myopia considered in this book were defined in previous chapters on epidemiology and screening. In addition to being potentially associated with changes in the fundus of the eye, uncorrected myopia has potential socioeconomic effects. According to the World Health Organization, it is one of the most important causes of visual impairment worldwide. Therefore, finding safe methods to mitigate this ametropia’s effects has medium and long-term social repercussions for society [1]. Photorefractive keratectomy (PRK) was the first excimer laser surface treatment introduced in the late 1980s [2, 3] and has been a technique used to correct myopia, hyperopia, and astigmatism for over 30  years. This technique involves mechanical epithelial removal, including removal of the epithelial basement membrane and subsequent laser photoablation of the Bowman layer and the anterior stroma [3]. The epithelial debridement can be done either with a mechanical scraping using a blunt spatula or a rotary brush, peeling the epithelial layer off after making it loosen through adjuvant alcohol 20%, or even using an excimer modality targeted

to epithelial removal in association with the excimer for the emmetropia correction (transPRK). Ideally, the epithelial removal diameter should exceed the excimer laser total ablation zone (optical zone + transition zone), which makes 9  mm or slightly more a recommended diameter reference (Fig. 4.1) [4].

Fig. 4.1  Illustrative photo of epithelial removal with a rotary brush. PRK technique involves mechanical epithelial removal, including removal of the epithelial basement membrane and subsequent laser photoablation of the Bowman layer and the anterior stroma

M. R. Santhiago (*) · L. P. Sampaio Department of Ophthalmology, University of São Paulo, São Paulo, Brazil © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. B. Randleman (ed.), Refractive Surgery for High Myopia, Essentials in Ophthalmology, https://doi.org/10.1007/978-3-031-40560-0_4

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Wound Healing after PRK Over the years, after an initial euphoria with the PRK technique, some cases of haze began to appear (Fig. 4.2). Part of the explanation for these cases was that deeper ablations (higher myopia) created more irregular stromal bed [5]. Studies in an animal model of subepithelial haze have demonstrated that surface irregularity and an associated defect in the regenerated basement membrane are associated with the development of haze after PRK,5 presumably because of increased penetration of epithelium-derived TGF-b, which is an essential trigger for myofibroblast generation from precursor cells and their long-term survival [6]. Depending on the level of attempted correction, the corneal wound healing response and the stimulus for the fibrotic response may be stronger after PRK, at least partly because of structural and functional defects in the epithelial basement membrane that occurs when there is greater surface irregularity after higher attempted corrections [7]. Mohan et  al. [8] studied keratocyte apoptosis, and the subsequent proliferation and generation of myofibroblasts were qualitatively and quantitatively different in PRK for high myopia compared with either PRK for low myopia or LASIK for high myopia. This study showed that the level of keratocyte apoptosis and the subsequent events of the stromal wound healing response were greater with higher levels of

M. R. Santhiago and L. P. Sampaio

excimer laser ablation of the ocular surface. In normal LASIK procedures, the basement ­membrane is left undamaged overlying the central cornea, and keratocyte apoptosis and the subsequent stromal healing responses are deeper in the stroma, far removed from the overlying modulatory epithelium and its supply of TGF-b needed for myofibroblast generation and survival [6]. The combination of more modern excimer lasers that leave smoother surfaces after ablation, even in cases of high myopia and deep ablations, and especially the adoption of mitomycin C (MMC), allowed PRK cases for high myopia to be performed in a way that the haze passed to be an infrequent event. [9] The smoother surfaces in the stromal bed (due to the modernization of the ablation processes) allow the formation of the basement membrane to occur appropriately, with no path of epithelial cytokines that functioned as a trigger in the process of creating myofibroblasts from fibroblasts and keratocytes [5, 9]. MMC modulates wound healing after PRK and other procedures as it is a potent mitotic inhibitor that effectively blocks keratocyte activation, proliferation, and differentiation of myofibroblasts. Many studies have suggested that MMC at 0.02% MMC concentration is safe and effective at the doses used by anterior surface surgeons [9, 10]. Although changes in the exposure time have less impact on the absorption of MMC by the cornea and aqueous humor than changes in concentration [11, 12], the drug is usually applied for 20 s to 1 min, depending on the ablation depth. In our practice, we keep it for 40–50 s in cases of high myopia [9].

Results for PRK in High Myopia

Fig. 4.2  Illustrative photo of stromal haze after photorefractive keratectomy for high myopia

With the modifications described above, PRK results in cases of high myopia have been shown to be safe, predictable, and effective even when followed for a long time [13–16]. Although the predictability of PRK in high myopia groups is comparable to low and moderate myopia groups, Alio et  al. showed that the effectiveness of the

4  PRK for High Myopia

PRK procedure up to −10.00 D of myopia decreases with time [16]. A meta-analysis comparing efficacy, predictability, safety, and visual quality of refractive corneal laser surgery demonstrated that all refractive surface laser surgeries were comparable in effectiveness, predictability, and safety [17]. When PRK is compared to LASIK for the treatment of high myopia, both techniques produced similar results 1 year after surgery [18, 19]. The comparison of PRK and SMILE in high myopia also showed similar results [15]. Although some authors advocate that SMILE demonstrated better astigmatic correction and lower spherical equivalent values than PRK, others did not find a statistical difference between them. Compared to phakic intraocular lens (IOL) implantation for high myopia, both techniques have reached similar levels of efficacy, safety, and predictability [20]. Hashemi et  al. [20] stated that phakic IOL implantation was better than PRK-MMC in correcting high myopia in terms of visual quality. Still, the two methods had no difference concerning visual acuity. They added that PRK-MMC could be used when the anterior chamber depth is a limiting factor in the implantation of phakic IOLs. In fact, some surgeons argue that if patients are good candidates for PRK, they would prefer the surface ablation procedure because it has fewer risks of intraocular complications such as cataract formation of endothelium cell loss.

 isual Recovery and Pain after PRK V for High Myopia Surface excimer ablation is associated with more postoperative pain and discomfort like tearing and photophobia. Studies show that post-PRK pain increases quickly after surgery, peaks 1–3  days postoperatively, and then decreases when reepithelialization is complete around 96 h after surgery. The pain is related to corneal nerve fiber exposure [21]. While some patients can be asymptomatic after the surgery, most report post-PRK pain, and

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a majority report the pain level as severe, at least for part of the recovery period [22]. A recent study summarized the best practices for postoperative photorefractive keratectomy (PRK) pain control. They showed systemic nonsteroidal anti-­ inflammatory drugs (NSAIDs) and opioid medications, topical NSAIDs, cold patches, bandage soft contact lenses, and topical anesthetics are all able to provide different and significant levels of improved pain control over alternative strategies and allow PRK-associated pain to be more tolerable for patients [23, 24]. Bandage contact lenses effectively reduced pain and promoted epithelial healing after PRK.  Regarding the contact lens material, senofilcon A showed greater pain control. In a high-magnification microscopy study, Taylor et  al. [24] BCL geometry and found the senofilcon A lens had a tapered edge with the thinnest profile of the lenses studied. This specific geometry was postulated to explain improved pain control with this CL model. Part of post-PRK visual stabilization is correlated with postoperative changes in epithelial thickness profiles. Previous studies have already shown that there is a correlation between greater central thickening (and stabilization time) and the amount of corrected myopia. Therefore, this role of the epithelium can be estimated as part of the explanation for cases that take time to stabilize in post-PRK eyes for higher myopia [25, 26].

 ctasia Risk with PRK for High-­ E Myopic Corrections One of the risk factors for post-laser vision correction ectasia in eyes with normal topography is weakening below a safe threshold. Estimating this limit through the percentage of altered tissue or PTA is possible. Santhiago et  al. coined the term, first proposed, investigated, and consistently determined the association between a high PTA value and risk of ectasia. The PTA represents a relative percentage contribution of the anterior stroma to the total corneal strength, which is modified after refractive surgery with the excimer laser [27, 28].

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In the case of LASIK, PTA = (FT + AD)/CCT where FT is the flap thickness, AD is the ablation depth, and preoperative CCT is the central corneal thickness. As corneal tensile strength presents an inhomogeneous distribution throughout the central cornea, removing the anterior part of the stromal may induce corneal weakening in increasing proportion as the threshold of 40% is reached and crossed [28]. Considering the elective nature and the young population associated with refractive surgery, it is advisable to lean toward a safer procedure. If topography is genuinely normal and a high PTA is the only identifiable risk factor, the surgeon could change the surgery to surface ablation, PRK, and even for high myopia, the PTA value would fall again within a safer range [28]. A recently published study by Sorkin et  al. [29] showed that eyes that would have been considered at higher risk for LASIK just due to a high PTA, and therefore had a high-myopic PRK with the application of MMC, presented safe, effective, and predictable results. For PRK, PTA can be described as: PTA  =  (Epithelium Thickness  +  AD)/ CCT.  Although we should not easily transpose the findings obtained by investigating eyes submitted to LASIK to eyes submitted to PRK, if preoperative topography is normal, the limits may be potentially higher in PRK because of its surgical structural differences (no flap cut and peripheral impairment of corneal fibers) [28, 30]. Considering the knowledge obtained so far, we still advise against any surgery in any surgical setting with high PTA. Although a safe procedure, the exact prevalence of ectasia in eyes subjected to PRK is not known. It should be noted that when choosing PRK for high myopia, the patient’s topography must be evaluated even more carefully since this high myopia is often accompanied by suspicious topographical patterns (or mildly altered) and thinner corneas. These in themselves are risk factors, and PRK is not a protective factor for ectasia (even with low PTA). Even though the risk is

M. R. Santhiago and L. P. Sampaio

likely lower than LASIK, cases should be evaluated with caution [31, 32]. The ideal scientific context to specifically investigate the role of PTA on ectasia after PRK would have eyes that developed ectasia after PRK with strictly preoperatively bilateral normal topography. However, most of these specific cases of ectasia after surface ablation occurred in eyes with suspicious preoperative or clearly abnormal topography or tomography [32–34].

 igher-Order Aberration Induction H after PRK for High Myopia The amount of induced coma in LASIK, PRK, and SMILE in the high-myopic groups are greater than in moderate myopia group when they are compared [35]. However, there is less induction of HOAs with PRK than with LASIK [36]. The evaluation of Femtosecond laser-assisted LASIK versus PRK for high myopia after 6  months of surgeries in terms of visual acuity and quality showed that the visual quality was worse in the LASIK group and patients had more induced coma aberration and reduced contrast sensitivity. Final visual acuity was better in the LASIK group than in the PRK group after 6 months, but those differences were not statistically different [37]. When the results comparing those techniques after 18  months were evaluated, we concluded that they also showed more HOAs in the LASIK group than in the PRK group. Because the regression rate after PRK was higher than LASIK, even without a statistical difference, some authors still recommended LASIK if possible in high-myopic patients [38]. To reduce visually significant induction of HOAs it is important to consider the final corneal curvature. We estimate that for each 1D treated of myopia we flatten corneal curvature by 0.9D, according to previous studies that showed 0.85D flattening in high myopia groups. A safe value that we should aim for the final correction for corneal curvature should be between 35 and 49D [39].

4  PRK for High Myopia

 efractive Regression after PRK R for High Myopia Undercorrection and refractive regression are more frequent in cases of high myopia. Ultraviolet (UV) light exposure during the initial postoperative period, use of oral contraceptives, and exacerbated scarring with haze formation are factors associated. In the first 3–4 weeks after surgery, if suspected, undercorrection should be treated by increasing the dose of topical corticosteroids with slow withdrawal [40, 41]. After the laser advances, we have better predictability of the surgery [42, 43]. Also, there was no correlation between amount of myopia and retreatment rate. The retreatment rate increased if patients were hyperopic or had astigmatism > or − 1.00D [44].

Retinal Detachment Risk with PRK Another concern among highly myopic patients is an increased baseline risk of rhegmatogenous retinal detachment (RRD). Detailed peripheral fundoscopy is mandatory in these patients. However, no studies have found an increased risk of RD after PRK, and a recent long-term study that analyzed more than 3000 patients concluded that PRK and LASIK did not affect the RRD prevalence in operated patients when compared to non-operated myopic eyes [45].

Conclusions PRK is a safe and predictable option for patients with high myopia, but a comprehensive screening exam is mandatory that includes evaluation of peripheral retinal pathology and corneal imaging. Furthermore, it is important to respect maximum ablation limits, PTA calculation, and final corneal curvature limits. The MMC 0.02% application after the excimer laser ablation for 20–30 s is also important for all high myopic ablations and can decrease the risk of haze formation.

35

References 1. Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, et al. Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology. 2016;123(5):1036–42. 2. McDonald MB, Liu JC, Byrd TJ, Abdelmegeed M, Andrade HA, Klyce SD, Varnell R, Munnerlyn CR, Clapham TN, Kaufman HE.  Central photorefractive keratectomy for myopia. Partially sighted and normally sighted eyes. Ophthalmology. 1991;98(9):1327–37. 3. Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg. 1988;14(1):46–52. 4. Shapira Y, Mimouni M, Levartovsky S, Varssano D, Sela T, Munzer G, Kaiserman I. Comparison of Three Epithelial Removal Techniques in PRK: Mechanical, Alcohol-assisted, and Transepithelial Laser. J Refract Surg. 2015;31(11):760–6. 5. Medeiros CS, Marino GK, Santhiago MR, Wilson SE.  The corneal basement membranes and stromal fibrosis. Invest Ophthalmol Vis Sci. 2018;59(10):4044–53. 6. Wilson SE. Biology of keratorefractive surgery- PRK, PTK, LASIK, SMILE, inlays and other refractive procedures. Exp Eye Res. 2020;198:108136. 7. Marino GK, Santhiago MR, Santhanam A, Torricelli AAM, Wilson SE. Regeneration of defective epithelial basement membrane and restoration of corneal transparency after photorefractive keratectomy. J Refract Surg. 2017;33(5):337–46. 8. Mohan RR, Hutcheon AE, Choi R, et al. Apoptosis, necrosis, proliferation, and myofibroblast generation in the stroma following LASIK and PRK.  Exp Eye Res. 2003;76:71–87. 9. Santhiago MR, Netto MV, Wilson SE.  Mitomycin C: biological effects and use in refractive surgery. Cornea. 2012;31(3):311–21. 10. Medeiros CS, Marino GK, Lassance L, Thangavadivel S, Santhiago MR, Wilson SE.  The impact of photorefractive keratectomy and Mitomycin C on corneal nerves and their regeneration. J Refract Surg. 2018;34(12):790–8. 11. Song JS, Kim JH, Yang M, et  al. Concentrations of mitomycin C in rabbit corneal tissue and aqueous humor after topical administration. Cornea. 2006;25:S20–3. 12. Song JS, Kim JH, Yang M, et al. Mitomycin C concentration in cornea and aqueous humor and apoptosis in the stroma after topical mitomycin- C application. Effects of mitomycin-C application time and concentra- tion. Cornea. 2007;26:461–7. 13. Tananuvat N, Winaikosol P, Niparugs M, Chaidaroon W, Tangmonkongvoragul C, Ausayakhun S. Twelve-­ month outcomes of the Wavefront-optimized photorefractive keratectomy for high myopic correction

36 compared with low-to-moderate myopia. Clin Ophthalmol. 2021;22(15):4775–85. 14. D’Oria F, Fernández-Buenaga R, Casanova L, García-Corral MJ, Vega A, Alio JL.  Surface ablation outcomes in high myopia with different epithelium removal techniques. J Cataract Refract Surg. 2021;47(9):1175–82. 15. Alio JL, Soria FA, Abbouda A, Peña-García P. Fifteen years follow-up of photorefractive keratectomy up to 10 D of myopia: outcomes and analysis of the refractive regression. Br J Ophthalmol. 2016;100(5):626–32. 16. Alió JL, Muftuoglu O, Ortiz D, Artola A, Pérez-­ Santonja JJ, de Luna GC, et al. Ten-year follow-up of photorefractive keratectomy for myopia of more than −6 diopters. Am J Ophthalmol. 2008;145(1):37–45. 17. Wen D, McAlinden C, Flitcroft I, Tu R, Wang Q, Alió J, et  al. Postoperative efficacy, predictability, safety, and visual quality of laser corneal refractive surgery: a network meta-analysis. Am J Ophthalmol. 2017;178:65–78. 18. Shortt AJ, Allan BDS, Evans JR.  Laser-assisted in-­ situ keratomileusis (LASIK) versus photorefractive keratectomy (PRK) for myopia. Cochrane Database Syst Rev. 2013;1:CD005135. 19. Gershoni A, Mimouni M, Livny E, Bahar I. Z-LASIK and trans-PRK for correction of high-grade myopia: safety, efficacy, predictability and clinical outcomes. Int Ophthalmol. 2019;39(4):753–63. 20. Hashemi H, Miraftab M, Asgari S. Comparison of the visual outcomes between PRK-MMC and phakic IOL implantation in high myopic patients. Eye (Lond). 2014;28(9):1113–8. 21. Garcia R, Torricelli AA, Mukai A, et al. Predictors of early postoperative pain after photorefractive keratectomy. Cornea. 2016;35:1062–8. 22. Palochak CMA, Santamaria J, Justin GA, Apsey DA, Caldwell MC, Steigleman WA, et  al. Assessment of factors associated with postoperative pain after photorefractive keratectomy. Cornea. 2020;39(10):1215–20. 23. Steigleman WA, Rose-Nussbaumer J, Al-Mohtaseb Z, Santhiago MR, Lin CC, Pantanelli SM, et  al. Management of Pain after photorefractive keratectomy: a report by the American Academy of Ophthalmology. Ophthalmol [Internet]. 2023;130(1):87–98. 24. Taylor KR, Caldwell MC, Payne AM, Apsey DA, Townley JR, Reilly CD, et al. Comparison of 3 silicone hydrogel bandage soft contact lenses for pain control after photorefractive keratectomy. J Cataract Refract Surg. 2014;40(11):1798–804. 25. Chen X, Stojanovic A, Liu Y, Chen Y, Zhou Y, Utheim TP.  Postoperative changes in corneal epithelial and stromal thickness profiles after photorefractive keratectomy in treatment of myopia. J Refract Surg. 2015;31(7):446–53. 26. Sedaghat MR, Momeni-Moghaddam H, Gazanchian M, Reinstein DZ, Archer TJ, Randleman JB, Hosseini SR, Nouri-Hosseini G.  Corneal epithelial thickness

M. R. Santhiago and L. P. Sampaio mapping after photorefractive keratectomy for myopia. J Refract Surg. 2019;35(10):632–41. 27. Santhiago MR, Smadja D, Gomes BF, Mello GR, Monteiro ML, Wilson SE, Randleman JB. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol. 2014;158(1):87–95. 28. Santhiago MR, Wilson SE, Hallahan KM, Smadja D, Lin M, Ambrosio R Jr, Singh V, Sinha Roy A, Dupps WJ Jr. Changes in custom biomechanical variables after femtosecond laser in situkeratomileusis and photorefractive keratectomy for myopia. J Cataract Refract Surg. 2014 Jun;40(6):918–28. 29. Sorkin N, Rosenblatt A, Smadja D, Cohen E, Santhiago MR, Varssano D, Yatziv Y. Early refractive and clinical outcomes of high-myopic photorefractive keratectomy as an alternative to LASIK surgery in eyes with high preoperative percentage of tissue altered. J Ophthalmol. 2019;28(2019):6513143. 30. Santhiago MR, Smadja D, Wilson SE, Krueger RR, Monteiro ML, Randleman JB. Role of percent tissue altered on ectasia after LASIK in eyes with suspicious topography. J Refract Surg. 2015;31(4):258–65. 31. Santhiago MR.  Percent tissue altered and corneal ectasia. Curr Opin Ophthalmol. 2016;27(4):311–5. 32. Randleman JB, Caster AI, Banning CS, Stulting RD.  Corneal ectasia after photorefractive keratectomy. J Cataract Refract Surg. 2006;32:1395–8. 33. Santhiago MR, Giacomin NT, Smadja D, Bechara SJ.  Ectasia risk factors in refractive surgery. Clin Ophthalmol. 2016;10:–20. 713. 34. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115(1):37–50. 35. Miraftab M, Hashemi H, Aghamirsalim M, Fayyaz S, Asgari S.  Matched comparison of corneal higher order aberrations induced by SMILE to femtosecond assisted LASIK and to PRK in correcting moderate and high myopia: 3.00mm vs. 6.00mm. BMC Ophthalmol. 2021;21(1):1–7. 36. Langrová H, Derse M, Hejcmanová D, Feuermannová A, Rozsíval P, Hejcmanová M.  Effect of photorefractive keratectomy and laser in situ keratomileusis in high myopia on logMAR visual acuity and contrast sensitivity. Acta Medica (Hradec Kral). 2003;46(1):15–8. 37. Hashemi H, Miraftab M, Ghaffari R, Asgari S.  Femtosecond-assisted LASIK versus PRK: comparison of 6-month visual acuity and quality outcome for high myopia. Eye Contact Lens. 2016 Nov;42(6):354–7. 38. Hashemi H, Ghaffari R, Miraftab M, Asgari S. Femtosecond laser-assisted LASIK versus PRK for high myopia: comparison of 18-month visual acuity and quality. Int Ophthalmol. 2017;37(4):995–1001. 39. Lombardo M, Lombardo G, Ducoli P, Serrao S. Long-­ term changes of the anterior corneal topography after photorefractive keratectomy for myopia and

4  PRK for High Myopia myopic astigmatism. Invest Ophthalmol Vis Sci. 2011;52(9):6994–7000. 40. Mohammadi S-F, Nabovati P, Mirzajani A, Ashrafi E, Vakilian B. Risk factors of regression and undercorrection in photorefractive keratectomy: a case-control study. Int J Ophthalmol. 2015;8(5):933–7. 41. Kitazawa Y, Tokoro T, Muramatsu R, Usui M, Sakimoto S, Sawa M.  Clinical results and complications of refractive surgery. Nihon Ganka Gakkai Zasshi. 1999;103(3):208–14. 42. Pokroy R, Mimouni M, Sela T, Munzer G, Kaiserman I.  Predictors of myopic photorefractive keratectomy retreatment. J Cataract Refract Surg. 2017;43(6):825–32.

37 43. Mimouni M, Kaiserman I, Spierer R, Spierer O, Rabina G, Varssano D, et  al. Factors predicting the need for re-treatment after laser refractive surgery in patients with high astigmatism: a large database analysis. J Refract Surg. 2021;37(6):366–71. 44. Randleman JB, White AJJ, Lynn MJ, Hu MH, Stulting RD. Incidence, outcomes, and risk factors for retreatment after wavefront-optimized ablations with PRK and LASIK. J Refract Surg. 2009;25(3):273–6. 45. Arrevola-Velasco L, Beltrán J, Rumbo A, Nieto R, Druchkiv V, Martínez de la Casa JM, et  al. Ten-­ year prevalence of rhegmatogenous retinal detachment in myopic eyes after posterior chamber phakic implantable collamer lens. J Cataract Refract Surg. 2023;49(3):272–7.

5

SMILE for High Myopia E. N. Wong and Jodhbir S. Mehta

Introduction Small Incision Lenticule Extraction (SMILE) is a refractive procedure involving the creation of an intrastromal lenticule with the VisuMax® (Carl Zeiss, Meditec, Jena Germany) femtosecond laser. Tightly focused patterns of femtosecond laser pulses are applied to form contiguous cut surfaces within the corneal stroma. The technology behind the SMILE procedure won Dr. Gerard Mourou and Dr. Donna Strickland the 2018 Nobel Prize in Physics for their method of generating high-intensity ultrashort optical pulses [1]. Four separate cuts are performed in succession— (1) lenticule posterior surface cut (horizontal plane); (2) lenticule side cut (vertical plane); (3) lenticule anterior surface cut/ cap cut (horizontal E. N. Wong Corneal and External Diseases Department, Singapore National Eye Centre, Singapore, Singapore Tissue Engineering and Cell Therapy Group, Singapore Eye Research Institute, Singapore, Singapore J. S. Mehta (*) Corneal and External Diseases Department, Singapore National Eye Centre, Singapore, Singapore Tissue Engineering and Cell Therapy Group, Singapore Eye Research Institute, Singapore, Singapore Department of Ophthalmology and Visual Science, Duke-National University of Singapore (NUS) Graduate Medical School, Singapore, Singapore

plane); and (4) opening incision side cut (vertical plane). Surgical extraction of the precisely shaped lenticule results in achievement of the desired refractive correction in the remaining intact ­cornea [2]. SMILE has gained wide acceptance as a safe and effective alternative to other established refractive procedures [3–6], with the company reporting more than 6 million procedures performed globally [7]. Unlike laser in situ keratomileusis (LASIK), there is no corneal flap creation or ablation of the corneal surface. This confers biomechanical advantages, improved ocular surface healing and reduced inflammation, and avoids potential flap-related complications [8–10]. In addition, there is reduced disruption of the sub-basal stromal nerve plexus, allowing for faster recovery of corneal surface innervation, and reduced postoperative dry eye [11]. Uncorrected myopia is the leading cause of visual impairment worldwide, with a projected 4.8 billion individuals with myopia and 938 million individuals with high myopia by 2050, according to one estimate [12]. The use of SMILE in patients with high myopia is of particular interest. For the purpose of this chapter, we define high myopia as a refractive error of −6.00D or more. This is a cohort of patients for whom conventional refractive surgery carries higher risk, and yet has the potential to bestow greater benefit. In a subset of patients with extremely high myopia of −10.00D or more, LASIK and advanced surface

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. B. Randleman (ed.), Refractive Surgery for High Myopia, Essentials in Ophthalmology, https://doi.org/10.1007/978-3-031-40560-0_5

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40

E. N. Wong and J. S. Mehta

Fig. 5.1  Example of a patient with high myopia, with axial lengths of 26.69 mm (OD) and 26.75 mm (OS), but shallow anterior chamber depths of 2.49  mm (OD) and

2.44 mm (OS), respectively. Such a patient would not be eligible for implantable collamer lens

ablation (ASA) are less commonly employed today. Phakic intraocular lens (pIOL) implantation, such as Implantable Collamer Lenses (ICL), is often considered in this setting. However, pIOL may not be suitable in all cases of high or extremely high myopia, such as in cases of long axial length but shallow anterior chamber depths, such as have been reported in Chinese popula-

tions (Fig. 5.1) [13]. SMILE is being explored as a safe and effective corneal-based refractive option to meet the needs of these individuals. Herein, we review and summarize the current understanding of the use of SMILE in high myopes in terms of visual and safety outcomes, complications, and current limitations and future directions for SMILE for high myopia.

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5  SMILE for High Myopia

 isual and Safety Outcomes V of SMILE in High Myopia Refractive and Visual Outcomes As of 2018, the US FDA approval for SMILE was for the reduction or elimination of myopia in patients aged 22 years or older, with stable manifest refraction over 1 year, spherical refractive error from −1.00D to −10.00D; cylinder from −0.75D to −3.00D; and mean spherical equivalent (MSE) no greater than −10.00D in magnitude [2]. Treatment range, according to the Zeiss website, is permitted up to a cylinder of 5.00D and MSE up to −12.50D [14]. FDA approval was granted based on a 12-month, prospective, multicenter, open-label, non-randomized clinical trial in 357 subjects that demonstrated excellent safety, predictability in regard to the intended outcome, improvement in

uncorrected distance visual acuity (UDVA), and refractive stability. At 12 months, 95.3% of eyes were within 0.50D of emmetropia, 89.0% achieved UDVA of 20/20 or better, and 99.0% had UDVA of 20/40 or better [15]. Outcomes of the use of SMILE in high myopia, however, may not be as predictable. A review of visual outcomes from 12 studies of SMILE in high myopia (−6.00D or more) performed from 2012 to 2018 found a range of results [16]. In eight of the studies, which had follow-up from 3  months to 1  year, the percentage of subjects with UDVA of 20/20, and spherical error (SE) within ± 0.50D, at study endpoint varied from 37 to 100% and 73 to 96%, respectively [17–24]. In the remaining four studies, which had longer-­ term follow-up from 2–5  years, those percentages ranged from 30 to 100% and 59 to 94%, respectively [16, 25–27]. Table  5.1 summarizes

Table 5.1  Demographic data on patients included in the study UDVA

No. Pre-op SE of (D) Mean Authors Year eyes Follow-up (range) Reinstein 2022 187 12 months −10.55 et al. [27] (−9.00 to −12.99) Zhao et al. 2022 40 5 years −7.49 [28] (−6.25 to −9.00) Tian et al. 2022 41 5 years −7.16 [3] (−4.25 to −10.00) Damgaard 2021 69 7 years −7.53 ±1.18 et al. [29] Lang et al. 2021 60 5 years −7.29 [31] (−6.00 to −9.13) Xia et al. 2020 35 4 years −10.06±0.64 [32] Elmassry 2020 495 3 years −12.84 et al. [33] (−10.00 to −14.00) Taneri 2020 62 3 months −9.10 et al. [35] (−8.00 to −11.38) Yang et al. 2019 53 15 months −9.78 [34] (−9.38 to −11.00)

Accuracy

Refractive stability

Lost ≥1 line (%) 4.00

SE ≤± 0.50D (%) 66.00

SE ≤± 1.00D (%) 93.00

Average regression (D/year) −0.08

≥20/20 (%) 57.00

≥20/25 (%) 82.00

CDVA Same or gained ≥1 line (%) 96.00

75.00

90.00

92.50

7.50

67.50

100.00 –

90.24

95.12

98.00

2.00

87.80

95.12

−0.03

51.90 67.00 81.00 19.00 59.40 (n = 14) (n = 14) 73.00 97.00 100.00 0.00 82.00

81.20

−0.05

95.00

−0.05

89.00

97.00

100.00 0.00

69.00

94.00

−0.06

–

–

94.00

6.00

–

–

−0.15

69.00

82.00

–

–

76.00

98.00

–

57.00

83.00

96.00

4.00

72.00

89.00

−0.19

E. N. Wong and J. S. Mehta

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the visual outcomes of more recent studies, not captured by the above review [28–36]. Follow-up duration varied from 12  months to 7  years. At study exit, the percentage of subjects with UDVA better or equal to 20/20 and 20/25 ranged from 57.0 to 90.2% and 82.0to 97.0%, respectively. In terms of refractive accuracy, the percentage of subjects falling within ±0.50D and ±1.00D of refractive target ranged from 59.4to 87.8% and 81.2to 100.0%, respectively. Correspondingly, rates of under-correction post-SMILE are increased in high myopes, as compared to mild and moderate myopes [19, 21, 35, 37, 38] and high myopia is a known risk factor for enhancement [39]. It has been suggested that the use of nomograms may improve outcomes [21, 40]. Burazovitch et al. used a correction factor of 8% of the initial total SE value, but despite this, still demonstrated eyes with a final under-correction [37]. Machine learning may play a role, and was shown to outperform an experienced surgeon's efficacy indices, with equivalent safety indices [41]. The higher prevalence of under-correction necessitates the employment of re-treatment strategies. The options are as follows: perform ASA, perform thin-flap LASIK within the anterior cap, or convert the cap into a FS-LASIK flap with a larger diameter than the original cap by using the VisuMax CIRCLE software [16]. ASA is often preferred as it preserves both the flapfree approach and the intended higher residual stromal thickness of the original procedure (Fig. 5.2) [39]. Astigmatic correction in high myopes has also been investigated. The lack of cyclotorsion control with the SMILE platform has raised concerns about the accuracy of astigmatic correction [16]. Pedersen et  al. found an under-correction of approximately 11% per diopter of attempted cylindrical correction in a cohort of 101 patients with myopic astigmatism [42]. This should be addressed in future developments of the laser platform. In terms of speed of visual recovery, there is evidence to suggest that in the immediate postoperative period (up to 2 weeks), this may be slower

for high myopes as compared to low and moderate myopes [37]. This is likely due to a delay in cap-to-bed realignment following the extraction of a thicker lenticule in high myopes. SMILE has been shown to have no impact on stereoacuity or accommodation in high myopia [43–45]. However, Zheng et al. reported a significant decrease in accommodative lag (i.e., improved accommodation) in a study of 32 patients with a mean (SD) age of 23.34 ± 2.90 years, and this was hypothesized to contribute to high patient satisfaction post-SMILE [46]. Overall, studies have shown that refractive outcomes in high myopia treated with SMILE are variable, with higher rates of under-correction than in low to moderate myopes, and preoperative counselling must take this into consideration. Despite this lower predictability in refractive outcomes, patient satisfaction rates remain high [47]. This is a cohort of patients for whom even under-correction may represent a dramatic improvement in their overall visual experience. Re-treatment strategies are available in cases of frank under-correction, with good outcomes [39].

Safety Outcomes In the clinical trial upon which FDA approval for SMILE was granted, no eyes had a loss of ≤2 lines of CDVA at 6 months (0 out of 348 eyes) and last visit (0 out of 357 eyes), respectively [2]. Of the nine recent studies in Table 5.1, the percentage of subjects for which CDVA remained the same or improved ranged from 81.0to 100.0%. It is worth noting that the study by Damgaard et al. with 7-year follow-up, was an outlier with a much lower percentage compared to the other eight studies [31]. One possible explanation is that this cohort had the highest average (SD) age, at 37 (8.1) years, therefore a proportion of patients would have been in their fifties at the time of 7-year follow-up. In addition, this study also did not use an optimized nomogram. 7.5% of subjects with high myopia in Zhao et al.’s study lost one line of CDVA, compared with 0.0% of subjects with moderate myopia [29].

5  SMILE for High Myopia

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a

b

Fig. 5.2  Case study. A 39-year-old female with high myopia first underwent maximal correction with SMILE, and subsequently had the residual refractive error corrected with ASA.  Initial refraction was −10.75/−1.75 × 175° (20/20) OD and −9.50/−2.50 × 180° (20/20) OS, with a central corneal thickness of 580  μm (OD) and 588 μm (OS). The following SMILE correction was programmed: −10.00/−1.75  ×  175° and −10.00/−2.50  ×  180°. Both eyes had an anterior cap of 110 μm and programmed optical zone of 6.2 mm. At 3 and 6  months post-SMILE, her refraction was stable at

−2.25/−0.75 × 20° (20/20) (OD) and −1.75/−0.75 × 10° (20/20) (OS). She then underwent SMILE enhancement, with advanced surface ablation using the Wavelight EX500 with a programmed correction of 2.25/−0.75 × 20° (OD) and −1.75/−0.75  ×  10° (OS). Three-month post-­ enhancement refraction was +0.50/−0.50  ×  25 (20/20) (OD) and +0.75/−0.25  ×  155 (20/20) (OS). The patient was 20/20 OU unaided. Final central corneal thickness was 466  μm (OD) and 402  μm (OS). (a, b) show the patient’s pre-SMILE and post-enhancement Pentacam images for her left eye, respectively

44

In a large study of 1574 eyes with preoperative MSE of −7.25 ± 1.84 D investigating safety outcomes, Ivarsen et al. found that at 3 months, 14% had a loss of one or more lines of corrected distance visual acuity (CDVA), and 1.5% of eyes lost two or more lines of CDVA. 50% of these eyes lost CDVA due to irregular topography and 12.5% were associated with a difficult lenticule extraction. However, at 18 months, all eyes were within one line of preoperative CDVA [48]. It was noted that a significant number of eyes with loss of CDVA occurred within the first 100 cases of the author, suggesting that surgeon experience may be a significant factor. Of the 24 eyes with loss of CDVA, 21 had recovered to preoperative levels at a late follow-up visit. Interestingly, topographic irregularities remained constant, suggesting that late compensatory mechanisms, such as epithelial remodelling or neuronal adaptation, may play a role in helping to mitigate the visual loss in these eyes [48]. Overall, SMILE in high myopia is a safe procedure. In instances of loss of CDVA, however, this is likely to be transient or treatable.

Long-Term Refractive Stability For prospective patients seeking spectacle independence over the medium to long-term, refractive stability is a key consideration and should factor into pre-operative counselling. In a long-term study of 69 eyes with high myopia that underwent SMILE, Damgaard et al. found that while visual outcomes remained stable over the follow-up period, there was significant refractive regression at 7  years. On average, −0.34 ±0.69 D was present, when compared to refraction 3  months post-SMILE.  This included data from three outliers with high myopic correction of < − 9.63 D and considerable regression (≥-1.50 D), but the finding was still significant, though reduced (−0.25 ± 0.49 D) even after they had been excluded [31]. Central corneal thickness, total corneal refractive power, and anterior average keratometry all significantly increased over that time period as well [31]. Numerous

E. N. Wong and J. S. Mehta

other studies have concurred, with varying rates of regression reported (see Table 5.1). There are a number of possible causes for regression, particularly in high myopes. Firstly, in some cases, the myopia may be progressive, with an increase in axial length. Ideally, this is screened for appropriate patient selection and when assessing preoperative refractive stability. Notably, Lang et  al. reported no significant changes in axial length following SMILE in highly myopic eyes over 5 years [32]. Secondly, epithelial and stromal remodelling may occur, causing a rebound steepening of anterior corneal curvature [49]. Small, but significant, amounts of regression may occur in the long term. This has been shown to happen to a greater extent in high myopia as compared to low and moderate myopia [49]. Epithelial remodelling, eye rubbing, and atopy may be factors too.

I mpact on Higher-Order Aberrations and Optical Quality The development of increased Higher-Order Aberrations (HOAs) following SMILE is well documented [19, 30, 50–52]. Significant increases in total HOA are predominantly driven by increased spherical aberration (SA), vertical coma, and trefoil. These then tend to remain unchanged, even up to the 5 year time point [30]. Microdistortions in Bowman’s layer have been observed in high myopes up to 2  years post-­ SMILE, the prevalence of which appears to be slightly higher than that previously reported in lower myopes (Fig. 5.3) [53–55]. It has been shown that the objective scatter index (OSI) significantly increases, while modulation transfer function cut-off frequency (MTFcutoff) and Strehl ratio (SR) significantly decreases up to 1 year post-SMILE [30, 50] but this appears to return to baseline levels at one and 5 years [30], and possibly earlier [56]. Also, more HOA, SA and trefoil were observed in patients with smaller optical zones (≤6.0 mm) compared to larger optical zones (> 6.0 mm) [57]. This is of

5  SMILE for High Myopia

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a

b

c

d

Fig. 5.3 Higher-order aberrations (HOAs) tend to increase more post-SMILE in high myopes than in low-­ moderate myopes. (a, b) pre- and post-SMILE HOAs in the right eye of a patient with MSE −11.63 D.  Positive spherical aberration increased from 0.150 μm to 0.287 μm,

and the absolute value of vertical coma increased from −0.099 μm to −0.653 μm. (c, d) –pre- and post-SMILE HOAs in a patient with MSE −3.00 D. Spherical aberration decreased from 0.110 μm to −0.201 μm, and vertical coma decreased from 0.155 μm to −0.121 μm

relevance, as some surgeons may opt to reduce the optical zone to conserve tissue for larger corrections in cases of high myopia. Changes in posterior cornea HOAs have not been demonstrated [19, 33, 58]. Given these increases in HOAs, it is unsurprising that a recent study found an increase in self-­ reported “quality of vision” (QoV) symptoms, particularly glare and starbursts. However, patient satisfaction levels and acceptance of QoV symptoms remained high (47), indicating that satisfaction is driven predominantly by visual acuity and residual refractive error.

Comparison to Spectacles and Contact Lenses A study compared visual image quality in high myopes treated with SMILE, spectacles, or contact lenses and found no loss of visual quality post-SMILE (based on visual Strehl ratio measured directly with wavefront aberrometry) [59]. The authors did, however, find that this measure was significantly worse in the patients with SMILE when compared to contact lens use, but not spectacle use. This finding was largely attributed to small residual uncorrected refractive error

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in the post-SMILE group [59]. These tests were carried out under scotopic conditions with large pupil sizes, and likely have minimal bearing on real-world visual experience. Indeed, in the same study, CDVA and contrast sensitivity between groups showed no differences. Furthermore, other studies have shown that self-reported vision-related quality of life is significantly better with SMILE compared to spectacle use [32, 60].

Comparison to Phakic IOL Insertion I mplantable Collamer Lens Implantable collamer lens insertion is an established alternative to corneal-based refractive surgery, and therefore is particularly useful in correcting high myopia [61]. The popularity of ICL insertion improved with the introduction of Central Flow technology (a 0.36-mm central port for aqueous flow). This has decreased the risk of cataract formation and eliminated the need for a peripheral iridotomy [62]. A meta-analysis of 12 studies involving 1390 eyes investigated outcomes between the Visian implantable collamer lens (ICL V4c, STAAR Surgical) and SMILE. No difference in efficacy or predictability was found, but ICL had a ­significantly higher safety index, lower HOAs, coma, and spherical aberrations. These differences were more prominent in patients with high myopia in the first 6  months post-operatively. After 6  months, differences in safety index and total HOAs became non-significant [62]. Contrast sensitivity (CS) and disc halo size have been shown to improve in both ICL and SMILE, with a greater improvement in CS at higher spatial frequencies [63]. In terms of patient-reported QoV outcomes, haloes appeared to be more common in the ICL group [63, 64], and starbursts in the SMILE group [63]. Moshirfar et al. compared outcomes between toric ICL and SMILE in patients with myopic astigmatism. Sub-group analysis of patients with very high myopia (−10.00 D or more) showed a significant difference in percentage of eyes achieving postoperative SE within ±0.50 D between the toric ICL eyes (66%) and SMILE

E. N. Wong and J. S. Mehta

eyes (100%). Furthermore, SMILE was better than toric ICL for cylinder correction within ±0.25 D, ±0.50 D, and ±1.00 D [65]. One possible explanation offered by the authors for this surprising finding was that in this subset, there were only 10 eyes that underwent SMILE, versus 68 eyes that underwent toric ICL [65]. However, the results from this study underlie the fact that SMILE is a valid alternative to toric ICL in very high myopes. SMILE has also been studied in comparison to the Artiflex pIOL in high myopic correction, with the Artiflex demonstrating slightly better safety and efficacy over 6  years, but with significant mean endothelial cell loss of 11.09% [66]. Both SMILE and ICL insertion have high safety and efficacy in correcting high myopia. Current best evidence seems to suggest that ICL insertion may have an edge in terms of safety indices in the short term, and the increase in HOA with SMILE needs to be taken into consideration.

Comparison to Femtosecond-LASIK (FS-LASIK) FS-LASIK is the most commonly performed refractive procedure in the world, with excellent safety profile, refractive outcomes, and rapid rehabilitation [67]. However, it carries the potential for flap-related complications, as well as the risk of ectasia following large ablations, often required in correcting high myopia. A meta-analysis of 12 studies [40, 58, 68–76] comparing SMILE and FS-LASIK, involving 1400 eyes with high myopia (≤-6.00 D), found that while both techniques were safe and efficacious with equivalent UDVA and mean refractive SE, the SMILE group had statistically significant superiority in terms of better CDVA, suggesting that there may be a safety advantage in SMILE over FS-LASIK in patients with high myopia. One of the included studies investigating patients with MSE from −10.00 D to −14.00 D additionally found less under-correction and less regression in SMILE patients over a relatively short follow-up period of 6  months [71]. Xia

5  SMILE for High Myopia

et al. also found significantly lower regression in SMILE compared to FS-LASIK over 3  years [68]. SMILE has been shown to induce lower total HOA and SA than FS-LASIK [51, 57, 77]. Other studies have concurred with the finding of lower total HOAs post-SMILE compared to FS-LASIK [78]. However, SMILE may induce more vertical coma [57, 68, 79, 80], and trefoil [51, 79], although contradictory findings have also been published [50]. This may be related to issues with centration of the lenticule intraoperatively. In terms of optical quality outcomes, SMILE has been shown to have lower reduction in Strehl ratio (SR), MTFcutoff and less increase in OSI than FS-LASIK [50]. It has been reported that there is a smaller decrease in functional optical zone (FOZ) with SMILE as compared to FS-LASIK [71]. This FOZ shrinkage has been shown to increase in a non-linear fashion with higher corrections [81, 82]. The FOZ is the area of the corneal surface that provides adequate quality of vision, and should, at minimum, be the size of the scotopic entrance pupil. Essentially, the FOZ is the area of the cornea that receives full correction [82]. A smaller decrease in FOZ with SMILE, compared to FS-LASIK, indicates that SMILE may be able to achieve better mesopic or scotopic vision for high myopes [71, 83]. This is especially relevant in the younger patients, who form the majority of refractive candidates and tend to have larger mesopic pupil size [84]. While there is evidence to suggest this difference in FOZ between SMILE and FS-LASIK may not translate to actual visual significance [85], one implication is that this parameter may be safely reduced in SMILE while maintaining a sufficiently large FOZ. The range of the programmed optical zone (POZ) in SMILE is 5.0–8.0  mm, but is commonly set between 6.0 and 7.0  mm [86]. The option to reduce the POZ in selected cases of high myopia would allow for greater preservation of residual stromal thickness. Figure 5.4 shows an example of a patient with high myopia undergoing SMILE, for whom a smaller OZ of 5.8  mm was used, compared to a more typical OZ of 6.5 mm.

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a

b

Fig. 5.4  Comparison of optical zones. (a) Conventional programmed optical zone of 6.5  mm; (b) reduced programmed optical zone of 5.8 mm used in a case of high myopia

There is a theoretical biomechanical advantage of SMILE over FS-LASIK, postulated to be due to the fact that the anterior stromal layers are left intact in SMILE [9]. A recent meta-analysis of 19 studies comparing biomechanical parameters in SMILE and other refractive surgeries found that corneal biomechanical strength was preserved better in SMILE than either LASIK or FS-LASIK, when measured with the ocular response analyzer (ORA). This difference was even greater after 12  months post-procedure, suggesting the possibility of better wound healing in SMILE [87]. However, the same meta-­ analysis found no significant difference in biomechanical outcomes when measured by the Corvis ST system, a finding that was consistent

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with the majority of this subset of studies [76, 88–90]. This inter-device discrepancy may be due to inherent limitations in the Corvis ST. Both SMILE and FS-LASIK are safe and efficacious treatments in high myopes. However, there appear to be clear advantages of SMILE, particularly in terms of lower regression, lower HOAs, and likely improved biomechanical strength.

E. N. Wong and J. S. Mehta

the early postoperative period and therefore has emerged as the more attractive option in this cohort.

 omplications of SMILE in High C Myopia Perioperative Complications

SMILE is a more technically demanding procedure as compared to other refractive surgeries. There is a steeper surgical learning curve that may be associated with an increased rate of periAdvanced Surface Ablation (ASA) shares similar operative complications [48]. Peri-operative biomechanical advantages and absence of flap-­ complications are related to lenticule creation related complications as SMILE. However, many and extraction, such as suction loss, opaque bubsurgeons shy away from the procedure over con- ble layer formation, black spots (Fig.  5.5), epicerns over slow recovery, longer medication regi- thelial abrasions, small tears at the incision, men, and risk of haze [91]. The risk of haze is of difficult lenticule extraction, and cap perforation. particular significance since it has been shown that the deeper ablation required in high myopes a increases this risk, as does myopic astigmatism [92]. Haze formation may be mitigated by the use of mitomycin-C intraoperatively, or by a prolonged course of topical steroids post-operatively [93]. Given these considerations, and that the FDA approval for photorefractive keratectomy and other advanced surface ablation techniques is for −6.0 D to −8.0D sphere and grade II

>grade III

ECD endothelial cell density, ICL implantable collamer lens, AD aqueous depth, AC anterior chamber

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6  Phakic Intraocular Lens (pIOL) in the Treatment of High Myopia Table 6.3  ECD and AD criteria for US FDA approved pIOLs

Age 21–25 26–30 31–35 36–40 41–45 >45

Visian ICL, EVO+ Minimum ECD AD ≥3.0 mm (cells/mm2) 3875 3425 3025 2675 2350 2075

Minimum ECD AD ≥3.2 mm (cells/mm2) 3800 3375 2975 2625 2325 2050

Minimum ECD AD ≥3.5 mm (cells/mm2) 3250 2900 2625 2350 2100 1900

Verisyse Minimum ECD AD ≥3.2 mm (cells/mm2) 3350 3175 2825 2500 2225 2000

ECD endothelial cell density, AD aqueous depth

tive. One year results indicated pIOL implantation was an effective and successful means of correcting refractive error without affecting best corrected visual acuity. Alio et al. also showed pIOLs (specifically Verisyse and Artiflex) can provide excellent visual results in patients with keratoconus with no significant difference in results [15]. A 3-year follow-up study indicated the safe, efficacious, predictable, and stable use of Visian toric lenses in patients with high myopic astigmatism and keratoconus (mean spherical equivalent −9.70 ± 2.33 D and astigmatism −3.21 ± 1.56 D) [16]. In a complex study of patients with severe keratoconus and post-LASIK ectasia (Stages II and III of Amsler-Krumeich classification), 31 eyes of 24 patients underwent a three-­ step surgical treatment with intracorneal ring segment implantation, corneal cross-linking, and implantation of toric pIOL, which improved visual acuity, high order aberrations (HOAs), and corneal shape [15]. These advanced procedures in complex patients require an experienced refractive and corneal surgeon with careful ­planning on a case-by-case basis along with close observation follow-up. Unstable or progressive keratoconus has been defined by some when the following occurs within 1  year: increase in astigmatism ≥1.0 D, significant changes in refractive axes orientation, an increase of 1.0 D or more in optical power of steepest meridian, decrease of 25 μm or more in corneal thickness [16]. In such circumstances, the mainstay treatment is corneal cross-linking,

which strengthens the collagen fibers in the cornea and stabilizes the progression of keratoconus. Patients will still have myopia after this procedure, and pIOLs may be a better alternative to LASIK and PRK surgeries for correcting refractive errors due to the unpredictability of corneal topography even after corneal cross-linking [17]. Izquierdo et al. utilized Artiflex pIOL in patients with progressive keratoconus (Amsler-Krumeich classification Grades I and II) following corneal collagen cross-linking, where 12-month follow­up showed 0.3 logMAR or better and statistically significant reduction in mean maximum and minimum keratometry values [18]. Phakic IOLs may also be used in patients who have undergone penetrating keratoplasty (PKP) or corneal transplant [19, 20]. A study by Alfonso et  al. describes 15 eyes receiving Visian Toric ICL or Visian ICL with stable refraction at least two years after PKP. Twenty-four month follow­up after ICL implantation showed 66% of patients were within ±0.50 D refraction goal. The endothelial cell loss in these patients was a mean of 4% loss per year over 2  years compared to the FDA ICL study showing a 3.2% loss per year over 3  years [11, 19]. A study of patients with only PKP showed a loss of 7.8%/year over a span of 3–5 years [21]. A study having 11 eyes with high ametropia after deep anterior lamellar keratoplasty (DALK) showed pIOLs were effective and safe over 3 years of follow-up. Average endothelial cell loss was 4.4%/year over 3 years, however, at a 5-year follow-up, one of these patients

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was sent for explantation due to significant endothelial cell loss [22]. Overall, patients with at least a year of stable refraction post-PKP may be candidates for an ICL implantation considering the non-significantly increased rate of endothelial cell loss. However, this is on a case-by-case basis and best clinical judgment must be utilized by the refractive surgeon. Long-term studies looking into post-PKP eyes with a pIOL implant should be assessed. Patients with presbyopia and myopia may be considered for a new type of phakic IOL for presbyopia called Implantable Phakic Contact Lens (IPCL), with refractive optic and diffractive trifocal pattern. These new types of lenses have multiple holes to facilitate aqueous flow from posterior to anterior. In a study of sixteen eyes, the most common complication was cataract formation in three eyes, one of which required cataract surgery. The endothelial cell loss at 12  months follow-up was 2.01% [23]. Another IPCL in 17 eyes, showed no cataract formation with an average cell loss of 9.9%/year over 2  years follow-up. The visual and refractive results were successful with high patient satisfaction due to freedom from spectacles [24]. However, authors note reversibility was a strong psychological factor for patients. Patients in both studies had some difficulties in dim light conditions, up to 40%. Only one patient suffered from glares and halos. Patients who have undergone prior LASIK but require further correction may be candidates for pIOLs implantation. A history of previous LASIK is not a contraindication to the use of pIOLs [25]. A multicenter study of 21 patients and 31 eyes undergone previous LASIK indicates EVO-­ Visian lens as providing safe, efficacious, and predictable outcomes and a surgical option for correcting residual refractive errors. At 6 months follow-up, 81% and 100% of eyes were within ±0.5 D and 1.0 D, respectively [26].

Contraindications for pIOL Patients must meet the criteria for specific pIOL implantation while meeting the ECD and AD

qualifications. In addition to these requirements, patients must be carefully assessed for any factors which may be contraindications for pIOL implant, including active anterior segment disease, cataracts, recurrent or chronic uveitis, glaucoma or elevated intraocular pressure > 21 mmHg, retinal pathology, iris or pupil function abnormalities, and previous ocular surgery [27]. Systemic diseases, which may alter the healing process, should also be assessed, including diabetes mellitus, and connective tissue or autoimmune diseases. See summary of pIOL inclusion and exclusion criteria in Table 6.4 [27].

Preoperative Testing and Lens Calculations To assess patient indications and contraindications, preoperative testing must be conducted including a comprehensive slit lamp, optical biometry, topography, and glaucoma and retinal evaluations [28]. It is important to note that the optical biometry, white-to-white (WTW) measurement, AS-OCT, and UBM discussed in this section Table 6.4  Summary of inclusion and exclusion criteria for pIOL implantation Inclusion criteria • Age ≥ 21 years (Verisyse) and 21–45 years (Visian). • Stable MRSE for 6 months (Verisyse) and 1 year (Visian). • Not a suitable candidate for refractive laser surgery based on MRSE or corneal depth. • AD ≥3.0 mm. • ECD, see Table 6.3. • AC angle (if ICL), see Table 6.2. • Mesopic pupil size 21 mmHg. • Retinal pathology. • Iris or pupil anomaly or function abnormalities. • Prior corneal or intraocular surgery, case-by-case. • Pregnant or nursing. • Uncontrolled systemic diseases such as diabetes mellitus, connective tissue disease, autoimmune disorders.

6  Phakic Intraocular Lens (pIOL) in the Treatment of High Myopia

occurs for the fitting of the ICL that is placed in the posterior chamber. The iris-fixated lens, Verisyse, placed in the anterior chamber, does not need any extensive size testing but simply needs to be symmetrical with the iris anatomy and achieve proper enclavation [13]. A slit lamp examination is used to evaluate lids, conjunctiva, cornea, anterior chamber, iris, and pupil morphology, while ruling out any cataract and zonular weakness. Optical biometry aids in the determination of important anatomical parameters such as axial length, AD, and white-to-white measurement. WTW measurement may be calculated manually or via a digital caliper. Topography is an essential tool for mapping before any refractive surgery where measurements such as corneal toricity, type of astigmatism present, and keratometry readings are required. These tools also help detect any corneal pathologies not suitable for surgery. The number of topography scans may vary among various clinical practices. For example, in a patient with keratoconus, stability must be ensured before even considering pIOL calculation due to risk and complications involved, in addition to change of future refraction. A stable topography is required over a minimum of two visits, with a stable refraction for 6  months, and no surgery for 2  years. Additionally, for patients who have undergone corneal cross-linking, pIOL would only be considered after at least 1 year of stable refraction and topography scans [29, 30]. For keratoconus

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patients, other criteria include a centralized cone, clear central cornea, and keratometric values ≤52.00 D. Glaucoma screening is necessary to detect any disc changes with or without tension and gonioscopy is essential to rule out angle closure or recession. A retinal evaluation would involve a dilated fundus exam to detect any degeneration and to rule out retinal and macular pathology. A comprehensive patient refraction must be measured in an undilated and dilated setting for each eye separately. Cycloplegic refraction is important to suspend accommodation since residual accommodation may produce suboptimal refractive results. It is also important to assess scotopic pupil size preoperatively to assess for patient predisposition to HOAs such as halos, starbursts, and glare in low-light conditions which may alter surgical planning and selection of pIOL with a larger optical zone size such as Verisyse Model 204 and Visian EVO+ ICL.  However, it is good to note many have argued against this concept. A varied number of exams, including those discussed above, may be conducted with an undilated or dilated exam shown in Table 6.5.

Specular Microscopy Specular microscopy is a noninvasive and important test for calculating ECD to detect any endothelial cell dysfunction, pathology, or cell loss. Due to

Table 6.5  Preoperative exams to be conducted in the undilated and dilated patient [28]

Undilated Manifest refraction Specular microscopy Corneal topography Glaucoma evaluation i-Trace Manual WTW measurement Optical biometry - UBM - AS-OCT

Dilated Dilated refraction Macular OCT Retina Evaluation

Note, the exams in orange are for the fitting of the Visian lens only, whereas the exams in black print are for both Visian and Verisyse lenses. In green is newer technology not yet widely utilized

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Fig. 6.2  A clinical specular microscopy image showing the number of endothelium in the right and left eye, along with values such as coefficient of variation (CV), hexagonality shape variability (HEX), number of cells in the

image (NUM), the thickness of cornea (PACH), and the size of cells with average (AVE), maximum (MAX), minimum (MIN), and standard deviation (SD)

a certain expected decrease in endothelial cell count after pIOL surgery, there is a minimum requirement for the endothelial cell count before any ocular surgery to prevent corneal edema. Thus, specular microscopy is used to exclude unsuitable candidates (Table 6.3) [13, 28, 31]. Fig. 6.2 shows a sample clinical specular microscopy image.

White-to-White The white-to-white (WTW) is an important measurement of the horizontal corneal diameter, measured from limbus to limbus as shown in Fig. 6.3. With newer technology, WTW can be automatically measured, which has been shown to be more accu-

6  Phakic Intraocular Lens (pIOL) in the Treatment of High Myopia

Fig. 6.3  Measurement of the WTW as shown by the green line drawn across the horizontal length of the cornea from limbus to limbus

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rate than manually due to examiner and patient variability with measurement and movement, respectively. Chen et  al. showed WTW measurements obtained by automatic devices to be smaller than those from manual calipers [32]. However, a recent study indicated the most accurate technique is to utilize automated and mechanical measurements [33]. It is recommended to cross-check automated and manual values at least three times [28]. Figure  6.4 shows the multiple automated values obtained by the device.

Fig. 6.4  Multiple automated measurements of WTW that are averaged together

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Ultrasound Biomicroscopy Ultrasound biomicroscopy (UBM) is another technique used to image the anterior segment of the eye, specifically the sulcus-to-sulcus (STS) distance that can be used to assess the predicted vault size and appropriate pIOL sizing with certain pIOL calculators. Figure 6.5 shows an example. UBM is considered to offer a more sensitive measurement compared to other techniques. Additionally, the UBM can be used to diagnose iridociliary cysts before and after surgery, although preliminary research by Chen et  al. found no relation between presence of cysts and ICL outcomes [34].

AS-OCT Anterior segment optical coherence tomography (AS-OCT) is a non-invasive technique measuring corneal shape, anterior chamber angle, angle to angle diameter, anterior chamber width, lens vault, and crystalline lens rise. These values all help determine the proper size and placement of the PC-pIOL.  The vault size is the distance

Fig. 6.5  A UBM scan of the right eye showing various measurements such as the anterior chamber width (ACW) at 11.72 mm which is the distance from sulcus-to-sulcus, angle recess area (ARA) at 55.9° and 44.5 °, the lens vault

M. Moshirfar et al.

between the crystalline lens and the posterior surface of the PC-pIOL.  The placement of the Visian, the posterior chamber pIOL, needs proper placement for an ideal vault size, shown in Fig.  6.6, between 250-750  μD, which can be determined by AS-OCT postoperatively [35]. Aberrometry or i-Trace is an advanced diagnostic machine that uses optical ray tracing to measure corneal, total and internal aberrations. It can also measure keratometric values. By isolating the internal aberrations, it allows for an evaluation of dysfunctional lens and can improve refractive and cataract surgery outcomes and improve the planning of intraocular lens implantation. However, it is important to note that this helpful tool is not required to perform pIOL implantation and is mainly utilized in settings of pseudophakic eyes. Various nomograms have been developed to aid in selecting the appropriate pIOL size, including the FDA Nomogram (also known as the manufacturer’s nomogram), Parkhurst Nomogram, Dougherty-Rivera Nomogram, and Optimized White-to-White nomogram. Each nomogram has different criteria to determine the selection of ICL size (Table 6.6). A study of 142 eyes and 73

(LV) at 0.60 mm, the distance from the lens to the posterior cornea, ACD (anterior chamber distance), and anterior cornea at 3.37 mm and 3.98 mm, respectively

6  Phakic Intraocular Lens (pIOL) in the Treatment of High Myopia Cornea Cross Line

Signal Strength Index 64

67 Right / OD

IR

Fig. 6.6  An AS-OCT scan of the right eye after placement of the ICL shows the Vault, longest distance between the back surface of the ICL and the front surface of the

natural lens, as 580 μm and other measurements between the two curvatures of the ICL and natural lens as 503 μm and 473 μm

Table 6.6  Shown are the FDA (Manufacturer’s), Optimized White-to-White, Dougherty-Rivera, and Parkhurst Nomograms along with their requirements for ICL size selection FDA (Manufacturer’s) nomogram White-to-White (mm) 3.5 All ≤3.5 >3.5 All ≤3.5 >3.5 All All

Recommended ICL size (mm) Not recommended Not recommended 12.1 12.1 12.1 12.6 12.6 12.6 13.2 13.2 13.2 13.7 13.7 Not recommended

ICL size (mm) 12.1 12.6 13.2 13.7 ICL size (mm) 12.1 12.6 13.2 (continued)

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68 Table 6.6 (continued) FDA (Manufacturer’s) nomogram White-to-White (mm) >13.0 If power of ICL is −3.00 to −7.50, use a larger threshold; if power is −8.00 to −16.00, use a smaller threshold Parkhurst nomogram If lens rise is normal (650,900 microns)

If lens rise is >900 microns

If lens rise is