Eyeworld

EW CORNEA 21 what's left in the cornea post-opera- tively." As a result, the ERSS is highly theoretical, he added. "Even my own studies on my patients show wide ranges for given/attempted thickness with a mechanical microkeratome," Dr. Binder said. "Mechanical microker- atomes cut deeper into the periph- ery, for the most part. Structurally, that could weaken the cornea even more, making it more susceptible to ectasia." Countered Dr. Randleman: "We do need further screening protocols. To the extent that Drs. Binder and Trattler looked into the subject, we applaud that. But looking at 1,700 patients without ectasia for 1 year does not invalidate the scoring sys- tem. In fact, in the three reported ectasia cases with abnormal topogra- phies from the Binder paper, all three manifested ectasia more than 2 years after surgery." Drs. Binder and Trattler, using Dr. Binder's patient data from a 13- year period between 1995 and 2008 with follow-up of "in excess of 30 months," used the ERSS on 1,702 eyes with myopic errors and bilateral normal topographies. 2 They found the ERSS would have eliminated 5.4% of eyes with a score of 4 or more from LASIK surgery and would have recommended the surgeon to advise an additional 6.8% of eyes with a score of 3 that they were at a "moderate risk." A total of 208 eyes (12.2%) with a risk factor score of 3 or higher with bilateral normal topographies would have been ex- cluded, yet not one developed ecta- sia, Dr. Binder said. In patients with bilateral normal topographies, the ERSS does not ap- pear to be an effective screening tool, Dr. Trattler said. "This is most likely based on the fact that a significant number of the eyes examined in the Randleman pa- pers had abnormal topography or were the contralateral eye to an eye with abnormal topography," he said. In Dr. Binder's patient data, three eyes of two patients developed ecta- sia, but all three had abnormal to- pography. The implication of the Binder/ Trattler paper "is that you should operate on people with elevated risk scores," Dr. Stulting said. "They sug- gest that you can operate safely on eyes that are potentially going to de- velop complications. My response is that as physicians, we should do no harm. We have a scientifically de- rived methodology to identify pre- operatively patients who are at higher risk to develop ectasia, and we should accept the low rate of false positives, 5% or so, that the system has in order to avoid a disas- trous complication in eyes at risk." Dr. Stulting added that he is not recommending people who have higher risk factors be considered in- eligible for surgery. "We can cer- tainly consider PRK and phakic IOLs for at least some of those eyes," he said. Moderate risk? "The ERSS suggests that those with a 3-point score would be at moderate risk, but we've never found out how many of those initial patients went on to develop ectasia," Dr. Binder said. "The ERSS also suggests you might want to recommend some- thing other than LASIK for those pa- tients with a score of 3 or more. But some other options may not be the best available." Clinicians need to evaluate the ERSS critically, Dr. Binder said. "An individual risk factor alone cannot determine whether or not an eye is at risk of developing ectasia. In my patient database, of those with a residual stromal bed of less than 240 microns and a risk of 3, none devel- oped ectasia," he said. What should clinicians consider the "most important point of the ERSS? That an abnormal topography is the single most important risk fac- tor," Dr. Binder said. "What's abnor- mal topography though? Surgeons aren't always in agreement about that. I may choose to operate on someone while another surgeon would opt not to based on that same topography. If topography is normal and the family history is normal, and the patient has no other abnor- malities in the eye when compared to the contralateral eye, the pre-op- erative central corneal thickness is 480 microns, etc., it's pretty safe to say that patient is not going to get ectasia." Dr. Stulting said, "Drs. Binder and Trattler repeatedly focus on flap thickness and topography as the only risk factors for ectasia. We don't think flap thickness alone is the only factor in predicting ectasia. In addition, thick flaps are not pre-op- erative risk factors, which the ERSS sought to identify." Dr. Trattler said that thick flaps "have been reported as a cause of ec- tasia in eyes with bilateral normal pre-operative topography." In his opinion, because flap thickness was not available in a majority of the eyes with normal topography (88% in the original ERSS database), the resulting ectasia may be classified as derived from pre-op risks or intraop- erative complications, but cannot be unequivocably stated as one or the other. Both Drs. Binder and Trattler agreed surgeons need a "better met- ric to define who is at risk," Dr. Binder said. The ectasia incidence in the U.S. has dropped dramatically as the field becomes more aware of the risk in eyes with abnormal topogra- phies, technology has helped clini- cians better interpret topography, and flap creation has become more standardized. Refractive surgeons worldwide are paying more atten- tion to topography overall, Dr. Binder said. "We need something better than the ERSS, but for now it's been an incredible help in pushing the issue to the forefront," he said. The two "hottest" areas of de- bate on the current ERSS remain pre- op corneal thickness and patient age, Dr. Randleman said. "They've been looked at in both papers," he said. "Neither paper says a relatively thin cornea excludes a continued on page 22 July 2011

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