EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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52 EW RESIDENTS January 2013 EyeWorld journal club Review of "Photorefractive keratectomy in patients with suspected keratoconus: Five-year follow-up" by Abigail T. Fahim, M.D., Lee M. Kiang, M.D., Andrew Stacey, M.D., Patricia A. Ple-Plakon, M.D., Blake V. Fausett, M.D., Courtney Kauh, M.D., Melisa Nika, M.D., Nicholas D. Chinskey, M.D., Alexandra O. Apkarian, M.D., Travis C. Rumery, D.O., Ira H. Schachar, M.D., Mehnaz Khan, M.D., Monica Michelotti, M.D., Vinod P. Mitta, M.D., Ryan Fante, M.D., Denise S. Kim, M.D., Crandall E. Peeler, M.D., S. Asha Balakrishnan, M.D., Michael L. Bullard, M.D., Molly L. Fuller, M.D., Kristen Harris Nwanyanwu, M.D., Duna Raoof-Daneshvar, M.D., and Shahzad Mian, M.D., residency program director Shahzad Mian, M.D., residency program director, W.K. Kellogg Eye Center, University of Michigan, Ann Arbor Does this paper provide the answer to an important question? This month, the W.K. Kellogg Eye Center, University of Michigan residents reviewed this interesting study of longer-term PRK outcomes in patients with early or forme fruste keratoconus. David F. Chang, M.D., chief medical editor Abigail Fahim, M.D., Lee Kiang, M.D., Patricia Ple-Plakon, M.D., Andrew Stacey, M.D. (back), Blake Fausett, M.D., Courtney Kauh, M.D., Melisa Nika, M.D., Nicholas Chinskey, M.D., Alexandria Akpkarian, M.D., Travis Rumery, M.D., Ira Schachar, M.D. P hotorefractive keratectomy (PRK) is a corneal surface ablation technique that consists of sculpting the corneal surface to alter the refractive power. Keratoconus (KC) is a relatively common non-in- Photorefractive keratectomy in patients with suspected keratoconus: Five-year follow-up Mikael Guedj, M.D., Alain Saad, M.D., Etienne Audureau, M.D., Damien Gatinel, M.D. J Cataract Refract Surg (January) 2013; 39:66-73 Purpose: To assess the long-range outcomes of photorefractive keratectomy (PRK) using functional and topographic criteria in myopic eyes with suspected keratoconus. Setting: Rothschild Foundation, Paris. Design: Retrospective interventional case series. Methods: Eyes of patients classified as keratoconus suspects or keratoconus by the Corneal Navigator software of the OPD-Scan II device were included. They were treated with myopic PRK using an EC-5000 excimer laser between 2004 and 2007. The main outcome measures were refractive stability, mean corneal keratometry, mean central pachymetry, mean thinnest point value, and the occurrence of post-operative complications such as corneal ectasia. Results: The study evaluated 62 eyes of 42 patients. The mean patient age was 34.6 years±15.1 (SD) and the mean spherical equivalent (SE), −3.96 ± 3.05 diopters (D). The mean central pachymetry was 529.4±32.8 µm and the mean simulated keratometry, 45.75±1.75 D. The percentage of similarity to keratoconus suspects or keratoconus was positive in all 62 eyes and exceeded a 50% similarity score in 30 eyes (48.4%). The mean follow-up was 4.8±1.4 years. The mean magnitude of the SE was −0.53±1.35 D over the follow-up. Two patients required glasses post-operatively because of significant myopic regression. No case of corneal ectasia was reported. Conclusion: Photorefractive keratectomy in eyes with suspected keratoconus based on a Placido neural network may be safe and effective for myopia and astigmatism in carefully selected patients. Source: Shahzad Mian, M.D. flammatory disorder, in which the apical cornea becomes progressively thin and takes on the shape of a cone. Surface ablation procedures are contraindicated in patients with known keratoconus; however, PRK is currently under study in patients with subclinical keratoconus or forme fruste keratoconus (FFKC). The authors1 present a retrospective case series evaluating the long-term safety, effectiveness, and occurrence of complications following PRK performed between 2004 and 2006 in 62 eyes of 42 patients with keratoconus or keratoconus suspect (KCS) as diagnosed by Placido topography analysis using the OPD-Scan II Corneal Navigator neural-network software (Nidek, Fremont, Calif.) at the Rothschild Foundation in Paris. The percentage of similarity to keratoconus suspects or keratoconus was positive in all eyes pre-op and exceeded 50% similarity score in 30 eyes. The mean follow-up period was 4.8 years. We commend the authors for undertaking the difficult task of helping to answer a question that many refractive surgeons are faced with, that of PRK safety in keratoconus suspects; however, there are many limitations of this study. One of the most important limitations of the study is that the authors do not define which criteria are used to diagnose keratoconus or keratoconus suspects. Videokeratography derived quantitative indices to detect early forms of keratoconus have been devised in the past with good clini- cal correlation. To detect keratoconus topographically, the use of multiple quantitative parameters is desirable. Rabinowitz2 suggests that a central K-value above 47.2 D and an I-S value greater than 1.4 D are suggestive of keratoconus. Maeda and Klyce3 suggest that a keratoconus prediction index (derived from eight other indices) greater than 0.23 is indicative of keratoconus. Rabinowitz/Rasheed4 suggest that a KISA% value between 60100% suggests the diagnosis of KCS (KISA% value is derived from the product of four indices: the K-value, an expression of central corneal steepening; the I-S value, an expression of inferior-superior dioptric asymmetry; the AST index, which quantifies the degree of regular corneal astigmatism; and the skewed radial axis index, an expression of irregular astigmatism). The authors in this paper do not use any of the above-mentioned indices in the study, which makes it difficult to define the patients being evaluated in the study and therefore the benefit of treatment. In addition, the mean percentage similarity scores for patients with KC or KCS are not impressive (33.13 and 27.84 for KC and KCS, respectively). Since the inclusion criteria are not well defined, the study is subject to selection bias. In addition, this is a retrospective case series study, which does not provide a comparison group, and therefore is unable to satisfy the requirement that treatment and control groups share similar prognosis, and leads to the