EyeWorld Asia-Pacific June 2021 Issue

REFRACTIVE 40 EWAP JUNE 2021 bed (RSB) thickness, age, preoperative corneal thickness (CT), and manifest refraction spherical equivalent (MRSE). “It’s a useful summary of the basics you want to look at, but it’s not the only thing you want to look at. “The addition of imaging systems like Pentacam [Oculus] and Galilei [Ziemer] that provide information on the posterior cornea is the other widespread revolution in understanding high-risk patients for LASIK. More recently the addition of epithelial mapping has been another valuable tool,” Dr. Schoenberg said, adding that he doesn’t have much experience with epithelial mapping yet. “Another tool that I don’t use routinely but I have in my arsenal is genetic testing. … We tend to think that most patients who get post- LASIK ectasia after successful surgery are probably patients who would have had some degree of subclinical or clinical keratoconus anyway.” Dr. Cosentino brought up irregular corneal topography as an important risk factor to watch out for. “Randleman et al. reported corneal topographic irregularity in 50% of the patients with corneal ectasia,” she said. 6 Candidacy for a refractive procedure is more than just preop testing. Dr. Schoenberg emphasized the safe ranges to which the cornea can be altered. Dr. Cosentino also mentioned the operative risk factors—a thin preoperative cornea and/or thick LASIK flap. Cordelia Chan, MD Consultant eye surgeon & partner, Eye Surgeons @ Novena Mount Elizabeth Novena Specialist Centre 38 Irrawaddy Road #09-28, Singapore 329563 drcordeliachan@gmail.com ASIA-PACIFIC PERSPECTIVES I remember clearly the day, fifteen years ago, when I diagnosed corneal ectasia in a patient I had performed LASIK on 2 years earlier. I was as sad and as devastated as the patient. The subsequent management of this one unfortunate patient was an invaluable journey of learning for me, and it has shaped the way I practice refractive surgery today. Fortunately, the incidence of ectasia after laser refractive surgery has decreased over the years, and this was discussed in the article “Technology, screening improvements decrease already low refractive surgery ectasia risk” originally published in the March 2021 issue of EyeWorld magazine. In 2001, the incidence of post-LASIK ectasia was reported to be 0.66%. 1 This decreased gradually over the years to 0.57%, then to 0.2%, and then 0.005%. 2–4 A recent large-scale retrospective review of 30,167 LASIK cases by Bohac et al. in 2018 puts the incidence of ectasia at 0.033%. 5 The declining incidence of ectasia can be attributed to a heightened awareness of the disease among refractive surgeons and the generation of better topography-tomography risk calculation indices and algorithms for detection of at-risk eyes. The use of the femtosecond laser for LASIK flap creation is also a contributory factor, with femto-flaps having better thickness predictability and planar flaps causing less biomechanical corneal weakening compared to the meniscus flaps of the microkeratome. Treatment preferences too have changed over the years with many refractive surgeons moving back to surface ablations, especially for eyes with suspicious topography or thin cornea. For higher myopic treatments, the procedure of choice has shifted to modern day posterior chamber phakic intraocular lenses which have excellent safety and efficacy profiles. Despite more than two decades of ectasia research, there is still uncertainty on the exact pathophysiological mechanisms governing the disease. We have seen cases with low preoperative risk factors going on to develop ectasia, while others with high odds remain stable, and ectasia has been known to occur in cases with no risk factors. 5,6 For most cases however, conventional risk factors exist, and in order to keep ectasia rates low, we must remain vigilant. In my practice, when assessing patients for refractive surgery suitability, I pay most attention to irregularities in topography and tomography, are more cautious in young patients with high myopia and/or astigmatism, and avoid LASIK in patients with cornea thickness of less than 500 µm. I also emphasize to my patients the importance of avoiding rubbing their eyes postoperatively, as eye rubbing has been postulated to be the triggering factor for ectasia in cases where classic risk factors are absent or not apparent. 5,7 The future of ectasia risk assessment lies in refining and combining existing risk-calculation algorithms, 6 with artificial intelligence and machine-learning systems likely to play a significant role. 7 Each case should be screened carefully using an individualized approach. With this, it is hoped that we will be able to further reduce the incidence of ectasia to as close to zero as possible. References 1. Pallikaris IG, et al. Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg . 2001;27:1796–1802. 2. Spadea L, et al. Corneal ectasia after myopic laser in situkeratomileusis: a long-term study. Clin Ophthalmol . 2012;6:1801–1813. 3. Rad AS, et al. Progressive keratectasia after laser in situ keratomileusis. J Refract Surg . 2004;20:S718–22. 4. Moshirfar M, et al. Rate of ectasia and incidence of irregular topography in patients with unidentified preoperative risk factors undergoing femtosecond laser-assisted LASIK. Clin Ophthalmol . 2014;8:35–42. 5. Bohac M, et al. Incidence and clinical characteristics of post LASIK Ectasia: A review of over 30,000 LASIK cases. Semin Ophthalmol . 2018;33:869–877. 6. Chan C, et al. Analysis of cases and accuracy of 3 risk scoring systems in predicting ectasia after laser in situ keratomileusis. J Cataract Refract Surg . 2018 Aug;44(8):979–99. 7. Ambrósio R Jr. Post-LASIK Ectasia: Twenty Years of a Conundrum. Semin Ophthalmol . 2019;34(2):66-68. Editors’ note: Dr. Chan declared no relevant financial interests.