EyeWorld India December 2013 Issue

40 EWAP CORNEA December 2013 Ectasia screening remains center of attention for refractive surgeons by Michelle Dalton EyeWorld Contributing Writer A spate of new studies brings attention back to this potentially devastating complication P ost-LASIK ectasia is rather uncommon (with estimates of the incidence well under 1%), but it can be a devastating complication, which may explain why so much effort has been put into trying to identify and weigh various risk factors. In 2008, the Ectasia Risk Study Score (ERSS) was published 1 and validated, yet the debate continues. The ERSS identified “multiple variables in a weighted fashion to improve screening strategies beyond topographic pattern and residual stromal bed thickness,” wrote Renato Ambrosio Jr., MD, and J. Bradley Randleman, MD, 2 but still generated 8% false negatives and 4% false positives in the original study populations. The ERSS (also known as Randleman’s Risk Score System, or RRSS) uses a combination of preoperative central corneal thickness, axial curvature maps of the front corneal surface, degree of myopia, the anticipated residual stromal bed, and the patient’s age to assess risk. The original ERSS acknowledged cutoff values for Views from Asia-Pacific Cordelia CHAN, MD Head and Senior Consultant, Refractive Surgery Service, Singapore National Eye Centre 11 Third Hospital Avenue, Singapore 168751 cordelia_chan@snec.com.sg P ost-LASIK ectasia: Still a bugbear of every LASIK surgeon “To do or not to do?” That is the question LASIK surgeons often ask themselves. At every preoperative evaluation for LASIK suitability, surgeons are essentially performing a risk assessment of each patient, determining the likelihood of the patient developing complications after surgery. The “comfort level” or “threshold” for LASIK varies from surgeon to surgeon, and is sometimes subjective rather than objective. The incidence of keratectasia after LASIK is estimated to be well below 1%, but due to its devastating consequences, post- LASIK ectasia remains one of the most feared complications of LASIK. The lower limit of residual stromal bed thickness (RSB)—which has been identified to be an important risk factor for ectasia—has, interestingly, increased over the years: from 200 microns in the early days of LASIK, to 250 microns, and now to 300 microns. However, cases of ectasia have been described with RSB over 300 microns, indicating therefore that there are other factors in play. In 2008, Randleman and co-workers published and validated an Ectasia Risk Study Score (ERSS), which identified multiple variables in a weighted fashion to improve ectasia screening, going beyond looking at topographic patterns and RSB. 1 The risk factors identified, in order of importance, were abnormal preoperative topography, low RSB thickness, young age, low preoperative corneal thickness, and high myopia. Although shortcomings exist in this scoring system, many surgeons including myself rely on it to help make that important decision on whether to proceed with LASIK. Ambrosio and co-authors in 2011 published tomography-derived pachymetric parameters to differentiate normal from keratoconic corneas. 2 Named Ambrosio’s Relational Thickness (ART), the parameters described as ART-Ave and ART-Max with cut-offs at 424 microns and 339 microns, respectively, serve as useful guidelines in determining “at-risk” corneas for LASIK. It is important to have a heightened awareness of “at-risk” patients, but it is also necessary not to overzealously exclude patients who may safely benefit from the life-changing spectacle and contact-lens independence that LASIK provides. It is a judgment call on the part of the LASIK surgeon. Certainly, when doubt exists, it is preferable not to proceed. References 1. Randleman JB, Woodward M, Lynn M, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmol. 2008;115:37-50. 2. Ambrosio R, Caiado AL, Guerra FP, et al. Novel pachymetric parameters based on corneal tomography for diagnosing keratoconus. J Refract Surg . 2011 Oct;27(10):753-8. Editors’ note: Dr. Chan has no financial interests related to her comments. continued on page 42