EyeWorld India June 2021 Issue

REFRACTIVE EWAP JUNE 2021 41 “In moderate myopes I start talking about and in higher myopes I recommend an implantable collamer lens,” Dr. Schoenberg said. “Rather than recommending a –9 LASIK, which is an on-label treatment, I would typically talk to that patient about an implantable collamer lens. That might be the shift in thinking that can change the [incidence of ectasia].” Dr. Cosentino also addressed percent tissue altered (PTA) as a factor to look at, with 40% PTA or higher being a risk factor for post-LASIK ectasia. “Marcony Santhiago, MD, proposed a metric for calculating the ectasia risk in patients who have undergone the LASIK procedure. 7 This metric can be expressed in terms of the following equation: PTA=(FT+AD) /CCT,” Dr. Cosentino said. As a cornea and refractive keratoconus specialist, Dr. Schoenberg gets a referral for ectasia after refractive surgery every couple of weeks, but he said most of these cases are 10-plus years postop. He said when he has the opportunity to review the preop testing on these patients with a current knowledge base, sometimes they are patients he would not recommend for surgery today. “In one case, the preoperative topography had a huge difference. It was a 3 D inferior vs. superior difference on the map. … The map that was sent to me was printed in 1 D steps. It matters because when you do big steps, everything smooths out,” he said, explaining the importance of using a scale with a high enough granularity to detect abnormalities. Dr. Schoenberg said the long- term safety data on refractive surgery offers confidence to patients, as well as the fact that there are treatments should the rare complication of ectasia arise postop. “I don’t minimize its risk but I do instill confidence about what we’re looking at before surgery and what we can do after surgery because if we have this condition that is unstoppable and scary, that’s very different from a condition that can be controlled and managed,” he said, explaining that crosslinking can effectively stop ectasia before it poses a significant problem. EWAP References 1. Seiler T, Quurke AW. Iatrogenic keratectasia after LASIK in a case of forme fruste keratoconus. J Cataract Refract Surg . 1998;24:1007–1009. 2. Randleman JB, et al. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology . 2003;110:267–275. 3. Rad AS, et al. Progressive keratectasia after laser in situ keratomileusis. J Refract Surg . 2004;20:S718–S722. 4. Pallikaris IG, et al. Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg . 2001;27:1796–1802. 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. Randleman JB, et al. Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening. Am J Ophthalmol. 2008;145:813–818. 7. Santhiago MR, 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;158:87–95. Editors’ note: Dr. Cosentino practices at Instituto de la Vision, University of Buenos Aires, Buenos Aires, Argentina. Dr. Schoenberg practices at Georgia Eye Partners, Atlanta, Georgia. Neither declared any relevant financial interests. Rohit Shetty, MD Vice Chairman and Head, Cornea and Refractive Services Narayana Nethralaya, Bangalore 121/C, Chord Road, 1st R Block, Rajajinagar, Bengaluru Karnataka, India-560010 drrohitshetty@yahoo.com ASIA-PACIFIC PERSPECTIVES Y ears after the introduction of refractive surgery, corneal ectasia is still the most feared complication post refractive procedure. Finding and analyzing most influential variables implicated in the development of ectasia may help us decrease its incidence. Though Randleman came out with risk scoring for ectasia, we have published case reports with normal topographies and biomechanics developing ectasia. Thus, the challenge lies in broadening the horizon on our approach and integrating all that we know. Pentacam and other topographers have multiple indices but we normally restrict ourselves to known indices such as BAD-D. We have published work on how artificial intelligence (AI) can help us predict progressors in keratoconus and this can be extrapolated to detect which topographies can lead to postoperative ectasia. Interestingly, the majority of the indices which were picked up were not indices such as BAD-D but asymmetry indices such as ISV, IHA, and IHD. Biomechanics is a useful tool and understanding indices such as CBI, TBI, SSI, etc. is important. AI does have an important role and we have built ACUSIMX, a simulation software that integrates AI and simulation modelling to predict postoperative stiffness changes post any refractive surgery and could be useful in predicting which corneas develop ectasia. The majority of what has been enumerated does not include a key aspect: the ultrastructural configuration of the cornea. Understanding collagen is important and seemingly normal tomography can still have reduced collagen and this can translate to post refractive ectasia. Custom built Ultrahigh-resolution Polarization Sensitive OCT, which gives us orientation and quantifies collagen, is a useful screening tool and though not all centers can possess one, we need to devise certain surrogate markers in each tool that can indirectly tell us about collagen, be it biomechanical or topographical. Epithelium can be a masquerader, and many times it can mask changes occurring at the stromal level which is where we need to focus. The key is to identify these epithelial irregularities preoperatively using tools such as Optovue or MS39. Even with normal topography and biomechanics, there could be other factors. We have published on the role of Lysyl oxidase (LOX), an endogenous crosslinker which is lowered in patients with corneal ectasia and was analysed using the tear cytokines and gene expression of preserved lenticules in cases of SMILE. Hence, preoperative screening using point-of-care diagnostic kits for levels of LOX and other factors such as MMP-9 can help look at eyes which are at risk for developing ectasia. The future is integrating AI with topography, biomechanics, and collagen and molecular markers for enhancing ectasia detection. Editors’ note: Dr. Shetty declared no relevant financial interests.