Eyeworld

EW CORNEA 20 July 2011 A still controversial subject, the ERSS has its pros and cons P rogressive corneal steepen- ing and thinning, coupled with progressive myopic astigmatism, has been termed "post-LASIK ecta- sia," especially if best corrected vi- sual acuity losses are incurred as well. As such, for years, refractive surgeons have been pouring over pa- tient outcomes to determine what the various risk factors may be. Un- deniably, pre-op topography is the most important parameter, and ab- normal topographies may suggest ectatic corneal disorders such as ker- atoconus, forme fruste keratoconus, or pellucid marginal degeneration. Recently, J. Bradley Randleman, M.D., associate professor, Emory University, Atlanta, and colleagues suggested a five-point ectasia risk factor scoring system that identified five primary factors. The top five risk factors (in order of importance) are abnormal pre-op topography, low residual bed thickness, young age, low pre-op corneal thickness, and high myopia. 1 In this system, each eye was evaluated independently, yielding two scores. Thus, a normal contralateral eye to one with forme fruste keratoconus would yield a lower risk score than the eye with keratoconus, although the authors recommended utilizing the worst of both eyes when making surgical planning determinations. The score system classified eyes with a score of 4 or higher as high risk, with a rec- ommendation against LASIK surgery. "The take-home point of the Ectasia Risk Score System [ERSS] is that ectasia is a risk and we do not have a good treatment for it," said Perry S. Binder, M.D., clinical pro- fessor, Gavin Herbert Department of Ophthalmology, University of Cali- fornia, Irvine. "In looking for the potential patients who have the risk, a comprehensive literature review— English papers only—reached certain conclusions about the popu- lation database." Dr. Randleman added the retrospective nature of the study meant not all the information was available for both eyes of all pa- tients, which explains why eyes were evaluated individually. Doyle Stulting, M.D., Woolfson Eye Institute, Atlanta, added, "An- other unique feature of the ERSS is its ability to evaluate multiple risk factors simultaneously. I have pre- sented cases in which the pre-opera- tive topography was absolutely normal, but the patient was young, the corneal thickness well within Dr. Binder's acceptable parameters but lower than average, and the residual stromal bed measured intra-opera- tively was OK—yet ectasia was the result. The ERSS was a strong predic- tor of ectasia in these cases with nor- mal topography and flaps we know were of normal thickness, when the other parameters considered in the ERSS were borderline." On the other hand, Dr. Binder commented that having no risk fac- tors does not guarantee one will not develop ectasia and conversely, if an eye has 4 or more risk factor points, for example, it does not mean that eye will develop ectasia. Drs. Randleman and Stulting are to be commended for their work on the topic and for being the first to try to develop a scoring system that can identify potential risk factors, Dr. Binder said. Their system sug- gests a score of 0-2 identifies people with a low risk of developing ectasia, a score of 3 indicates moderate risk, and a score of 4 indicates a high risk for developing ectasia. (The number of possible points ranged from 0-10 in the original ERSS analysis, Dr. Binder added.) "Basically, we used accepted sta- tistical methodologies to evaluate differences in pre-operative parame- ters between those patients with ec- tasia and those without," Dr. Randleman said. "We used patients with uneventful LASIK with a 1-year follow-up as the control group. Longer follow-up would have been ideal; however, in refractive surgery, we usually don't have consistent routine follow-up longer than that. Ectasia is a more difficult complica- tion to study because it is a rare complication and frequently occurs many years after seemingly unevent- ful surgery." He said it's analogous to the re- lationship between smoking and lung cancer—only 5-10% of those who smoke will develop lung cancer, so if you only look at a group of smokers, very few will have lung cancer, therefore making smoking look like a low risk factor for devel- oping lung cancer. Yet about 90% of those with lung cancer have smoked; thus, when looking at a group with lung cancer, it is clear that smoking is a significant risk for the disease. "It depends on from which di- rection you look at the issue. The ev- idence can show a clear risk, even if the majority of people with that risk never develop the disease," Dr. Randleman said. A differing perspective However, some physicians disagree with recommendations of the ERSS. 2 Evaluating each eye separately is not ideal, said William Trattler, M.D., cornea specialist, Center for Excel- lence in Eye Care, Miami. A scoring system that evaluates ectasia pa- tients with bilateral normal topogra- phies would be more reflective of patients undergoing LASIK in 2011, since patients with forme fruste ker- atoconus, keratoconus, or pellucid marginal degeneration in either eye are excluded from LASIK, he said. Another concern in applying the ERSS to today's patients is that all cases in the ERSS had surgery with a mechanical microkeratome, he said. "In 2011, flap-creating technol- ogy is more advanced than it was when most of the ERSS ectasia cases had surgery," Dr. Trattler said. Fem- tosecond lasers can create thin, planer flaps, which have been shown to cause less corneal weaken- ing than meniscus-shaped flaps cre- ated with metal microkeratomes, he said. In Dr. Stulting's hands, however, using a microkeratome versus a fem- tosecond laser is a non-issue. "I have the same standard deviations in pa- tients who had microkeratome- based flaps as those obtained with femtosecond-based flaps," said Dr. Stulting. "Furthermore, the flaps are planar." Dr. Trattler counters that while the microkeratomes in use today are capable of making planar flaps, those most commonly used from 1996-2003 created meniscus flaps and, as such, had standard devia- tions much greater than is typical of the IntraLase Femtosecond Laser (Abbott Medical Optics, AMO, Santa Ana, Calif.). Dr. Binder added that "most publications comparing mi- crokeratomes have had the opposite conclusion [from Drs. Stulting and Randleman]." He added mechanical microkeratomes can be sensitive to corneal pachymetry, curvature, IOP, and other factors. While some cases of ectasia "have been due to unexpectedly thick flaps, flap thickness is not a pre-operative risk factor and cannot be used to estimate the risk of ecta- sia before surgery," Dr. Stulting said. One of the more controversial issues with the ERSS is that 88% of the patient chart data used was without measured flap thickness, Dr. Binder said. "Without knowing what the measured versus intended flap thickness is, you cannot know by Michelle Dalton EyeWorld Contributing Editor Ectasia risk score system Topography of a patient with post-LASIK ectasia who had pre-op forme fruste keratoconus. The five-point ERSS identifies primary ectasia risk factors Source: William Trattler, M.D.

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