EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/78708
32 32 EW REFRACTIVE SURGERY June 2012 A refractive surgery case study Refractive editor's corner of the world by Faith A. Hayden EyeWorld Staff Writer One patient, three opinions L ASIK has come a long way since its arrival in the mid 1990s. We have progressed from broad beam abla- tion to scanning or variable spot movements. The lasers all now use tracking devices to follow eye movements. Wave- front-guided and optimized procedures are now mainstream. Mechanical microker- atomes have improved, and currently fem- tosecond lasers are the most frequently used devices to create flaps. All of these developments have led to improved safety and better outcomes for our patients. Diagnostic devices have also im- proved. We now have improved Placido disc imaging and scanning optical slits and Scheimpflug imaging to best evaluate the posterior corneal surface and corneal eleva- tions. While we have improved ability to screen for at-risk patients, especially pa- tients at risk for corneal thinning, forme fruste keratoconus, and an unpredictable outcome, our screening is not and cannot be 100%. Without the ability to actually biopsy a cornea and examine the tissue, and until we can use non-invasive tech- niques more effectively, corneal topography continues to be the gold standard LASIK screening device. Inherent in theses devices are flags or warning signs that many feel will over-call things. What to do in these circumstances? While there may not be much perceived clinical risk, there can be medico-legal risk. Is this an informed con- sent issue? These commonplace questions arise weekly in almost every refractive practice. In this month's "Refractive corner of the world," we present a fairly standard case of a 21-year-old low-moderate myope who desires LASIK refractive surgery. Her topography looks fairly typical for what we see in everyday practice. Yet there are a few "yellow flags," in this case, the progression of pachymetry from the BAD screen on the Pentacam. Can this patient be treated with LASIK? Is this an informed consent issue? Is there a medico-legal issue, a patient safety issue, or both? I am pleased to have three experts, Michael W. Belin, M.D., Louis Probst, M.D., and Richard L. Lindstrom, M.D., provide some insight into these diagnostic dilemmas. Kerry Solomon, M.D., refractive editor A 21-year-old female soft contact lens wearer pres- ents in your practice as a candidate for refractive surgery. Her contacts have been out for 2 weeks and the refrac- tion is about –3.25 sphere in both eyes. EyeWorld presented this history along with two topographies to three refractive surgeons and asked for their recommendation on the following question: Is the patient acandidate for refractive surgery? Michael W. Belin, M.D., profes- sor of ophthalmology and vision sci- ence, University of Arizona, Tucson; Louis Probst, M.D., chief laser sur- geon, senior medical advisor, TLC Laser Eye Centers, Chicago; and Richard L. Lindstrom, M.D., adjunct professor emeritus, ophthal- mology department, University of Minnesota, Minneapolis, and founder and attending surgeon, Minnesota Eye Consultants, Minneapolis, weighed in. Dr. Belin: "This is a young fe- male moderate myope who presents for a refractive surgery evaluation. She has four maps (two for each eye) from the Humphrey Atlas [Carl Zeiss Meditec, Dublin, Calif.]. I no longer use, and have not used for over 5 years, any Placido-derived topogra- phies, believing that accurate eleva- tion systems have for the most part supplanted the need for Placido analysis. "The four-map composite dis- play (anterior curvature, anterior and posterior elevation, and corneal thickness) is a commonly used dis- play by many. The third display ('refractive') is one that I do not rec- ommend using, as it was designed with anterior curvature indices to mimic a Placido system and does so with the same false positives and false negatives associated with Placido-derived anterior curvature. "The BAD display shows a nor- mal anterior elevation, which is why you have a normal reading Placido analysis and a normal posterior ele- vation. The thinnest points are 516 and 524 OD/OS, and the elevation values at the thinnest point are well within normal levels. "The area of concern is in the pachymetric progression. Both eyes have PTI (Percentage Thickness In- crease) tracings that fall below the 95% confidence interval, and the An image from the Pentacam using the BAD II analysis Source (all): Kerry Solomon, M.D. Progression Index (max) OD is 1.53, which is high. The Ambrosio Rela- tional Thickness (ARTmax) (thinnest point/PImax) is 337. These values (PTI graph, PImax, and ARTmax) are borderline values, which is why the overall reading of these maps is roughly 1.8 SD from the norm and flagged as 'yellow.' "Based on the current exams, I would not perform LASIK, in part due to the age of the patient com- bined with the borderline BAD dis- play. The overall correction (SE –3.62/–3.46) is low enough to easily consider surface treatment, but I would still want documented tomo- graphic stability over time before proceeding. If treated, I would also consider conventional treatment (for tissue saving) as both the cylin- der and high order aberrations are very low. When the U.S. catches up with the rest of the world, this may be a good example of where prophy- lactic crosslinking would be applica- ble." Dr. Probst: "This is a fantastic demonstration of the conundrum that is created with our advanced screening tools. As a low myope with reasonable pachymetry and normal topographies, this patient appears to be an excellent candidate for LASIK. While the [Carl] Zeiss continued on page 35 Atlas topography with Pathfinder II analysis. This shows normal topography with a high likelihood of a "normal" topography and no signs statistically of suspect keratoconus