OCT 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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36 36 EW REFRACTIVE SURGERY October 2012 Tackling residual refractive error with PRK after corneal transplantation by Maxine Lipner Senior EyeWorld Contributing Writer Considering PRK in place of LASIK I t's one of those problems that perpetually face practitioners after performing a corneal transplant for keratoconus— what to do about residual re- fractive error, a virtual staple of the procedure. Almost all patients will have some refractive error following a penetrating keratoplasty, according to Gerard Sutton, M.D., Sydney Medical School Foundation profes- sor of corneal and refractive surgery, Save Sight Institute, Sydney Univer- sity, and Vision Eye Institute, Syd- ney. "It is a major problem following penetrating and also deep anterior lamellar transplant," Dr. Sutton said. Astigmatism is the leading difficulty here, he finds. "It averages out at 3-4 D in most series," he said. "In my published series of 2008 of 100 con- secutive corneal transplants for kera- toconus, the mean astigmatism was 2.8 D." He found that in the series, 42% of patients attained 20/40 uncorrected. However, with the aid of glasses, by the 3-month mark this had climbed to over 95%. Exploring PRK here The natural answer seemed to be refractive surgery to correct residual error. While LASIK seemed feasible, Dr. Sutton had concerns. "We had previously investigated and pub- lished on the use of LASIK for refractive errors after penetrating keratoplasty," he said. "The results were reasonable, but there were con- cerns about post-LASIK ectasia, pre- dictability, and epithelial ingrowth." Dr. Sutton and fellow investigators postulated that PRK when used with mitomycin-C would be superior in all of these areas. To help consider this, investiga- tors launched a consecutive case series that included 47 eyes of 41 patients. In retrospectively reviewing the data, patients were divided into two groups. Those with pre-op re- fractive cylinder of less than or equal to 6 D were placed in the low cylin- der group and those with greater than 6 D in the high cylinder group. "In this study we waited until Corneal graft in the early post-op period following surface ablation there had been refractive stability after suture removal at an average of 12 months," Dr. Sutton said. "We then attempted to treat 90% of the spherical error and all of the astig- matism." To reduce post-op haze, investigators applied mitomycin-C for 30 seconds and left a bandage contact lens in situ for 4 days. In addition, ciprofloxacin eye drops were used for 1 week and fluo- rometholone for 3. Results published in the Journal of Refractive Surgery1 showed that Corneal graft with sutures Source (all): Christopher Hodge after treating these patients with PRK, the spherical equivalent decreased from –4.24 D pre-op to just –0.71 D 12 months post-op in the low cylinder group and from –4.19 D to –2.45 D in those with high cylinder pre-op. When it came to refractive cylinder following PRK treatment, this decreased from –4.27 D to –1.71 D for those with low cylinder and from –7.78 D to –4.6 D for those in the high cylinder group. Patients did face some complica- tions. Investigators found that 8.3% of patients had lost two lines of cor- rected distance visual acuity. "There were no cases of corneal haze greater than 2+ or of graft rejection," Dr. Sutton said. He sees the most troubling prob- lem here as the loss of distance acu- ity in some. "The main issue was loss of best corrected vision in 8% of patients," he said. "I think that this can be improved upon with the use of topographically guided treat- ments." With this in mind, investi- gators are now looking at a modified approach. "We have begun a study looking at how judicious use of topographic-based treatments could improve outcomes in these pa- tients," Dr. Sutton said. He hopes that this will ensure that many such patients do not lose uncorrected lines of correction. PRK preferences Dr. Sutton views PRK as likely safer here than LASIK, but from a clinical perspective, the latter does have one advantage. "The main advantage of LASIK is speed of recovery," he said. There is, however, another tradeoff, with outcomes tending to be more variable with LASIK in cases where all of the treatment is done at once. "The creation of the cap adds a variable in cylindrical corrections, which is difficult to control for in unstaged treatments," Dr. Sutton said. He hopes that practitioners come away from the study with the understanding that PRK is a viable option in such corneal transplant cases. "PRK with mitomycin-C is effective in reducing post-graft refractive errors," he said. When compared with the published litera- ture, investigators concluded that this was probably safer than LASIK for these patients. Going forward, Dr. Sutton hopes that in the future, acuity for such patients can be further improved. "I think that the use of surface topo- graphically guided or ray tracing- based treatments will greatly improve outcomes," he said. EW Reference 1. Hodge C, Sutton G, Lawless M, et al. Photorefractive keratectomy with mitomycin-C after corneal transplantation for keratoconus. J Cataract Refractive Surg. 2011: 37:1884-94. Editors' note: Dr. Sutton has no finan- cial interests related to this article. Contact information Sutton: gerard.sutton@vgaustralia.com

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