PRK Enhancement with Mitomycin - C after LASIK - a case series Dr G.B.Kaye MD,FRCSC Dr R. Dalvi MS,DNB Gimbel Eye Centre Edmonton,Canada The Authors have no Commercial Interest to declare

INTRODUCTION Laser in situ keratomileusis (LASIK) is a procedure commonly used for the correction of ametropia. Photorefractive Keratectomy (PRK), however, is often preferred when limited corneal bed thickness is an issue. In this case series, PRK was performed over LASIK due to insufficient residual bed depth for a LASIK enhancement procedure.

PURPOSE To evaluate the efficacy and safety of PRK for the treatment of refractive errors which were residual, or due to regression following previous LASIK surgery in which insufficient bed remained for LASIK enhancement.

MATERIALS & METHODS In this single center, retrospective, observational case series, 6 eyes of 5 patients (mean age 46.6 years) were evaluated that had had PRK for the treatment of residual refractive error or refractive error due to regression following previous myopic LASIK surgery. The NIDEK EC 5000 (Gamagori, Japan) was used for the enhancement procedures. All eyes underwent slit-lamp biomicroscopy, refraction, pachymetry, pupillometry, and corneal topography pre- and post-operatively. All eyes were followed up at 3 days, 1 week, and monthly for 6 months. Mitomycin-C (0.02%) was used in all cases, immediately following the PRK procedure.

TECHNIQUE PRK The standard technique was used as in the case of PRK enhancements. The epithelium was removed using a Paton spatula after soaking the epithelial surface with 50% alcohol for 10 seconds. Care was taken to scrape the epithelium from the corneal surface in the direction away from the hinge of the LASIK flap. This was followed by laser treatment done with the NIDEK EC 5000 laser.   Mitomycin – C (0.02%) was applied to the corneal surface for 30 seconds after completion of the laser treatment. A bandage contact lens was placed after instillation of Vigamox, FML 0.1% and Voltaren drops. The eyes were seen again on the third post operative day. All eyes were placed on a tapering schedule of FML 0.1% drops for 3 to 6 months following the PRK enhancement procedure. Two eyes had had Intralase LASIK rather than blade LASIK as the primary procedure.

RESULTS The mean interval between the LASIK surgery and the PRK enhancement was 35 months (range: 9 to 84 months). At 4 months follow-up (post-PRK), the average UCVA had improved from 20/60(range: 20/25 to 20/125) pre-operatively to 20/25(range: 20/20 to 20/40). Two eyes had grade 1 sub-epithelial haze observed at 2 months postoperatively which resolved spontaneously over the ensuing months. One patient (2 eyes) was diabetic but did not show any post operative complication. Mean spherical equivalent attempted correction with PRK was - 2.00 diopters (D) (range: - 1.00 to - 3.1D) which improved post-operatively to a spherical equivalent of - 0.61D (range: +0.5 to - 0.87D).

SUMMARIZING TABLE Initial Pachymetry Flap thickness   Initial Pachymetry Flap thickness Post LASIK Bed Depth Pre LASIK SE (D) SE (D) Post PRK SE(D) UCVA Pre PRK Final UCVA, 4 months BCVA, Post PRK DF 538 microns 160 microns 268 microns -7.5 -3.125 -0.67 20/125 20/30 20/20 553 microns 263 microns -6.67 -1.75 -0.25 20/40 DG 485 microns 223 microns -5.00 -2.00 -0.87 20/70 20/25 20/15 LH 528 microns 237 microns -7.87 -2.50 1.00 KH 509 microns 110 microns 276 microns -6.12 -1.00 0.00 SS 532 microns 289 microns -6.87 -1.625 -0.12 20/50   Initial Pachymetry Flap thickness Post Lasik Bed Depth Pre LASIK SE (D) Post LASIK Post PRK SE(D) UCVA Pre PRK Final (4 months) BCVA DF 538 microns 160 microns 268 microns -7.5 -3.125 -0.67 20/125 20/30 20/20 553 microns 263 microns -6.67 -1.75 -0.25 20/40 DG 485 microns 223 microns -5.00 -2.00 -0.87 20/70 20/25 20/15 LH 528 microns 237 microns -7.87 -2.50 1.00 KH 509 microns 110 microns 276 microns -6.12 -1.00 0.00 SS 532 microns 289 microns -6.87 -1.625 -0.12 20/50

CONCLUSION PRK enhancement with the adjunctive use of Mitomycin-C (0.02%) is safe for treating myopic regression and residual refractive error following previous LASIK. There was no long term clinically significant haze in any of the eyes in the study. All eyes showed improvement in UCVA following the procedure.  

REFERENCES 1 Photorefractive keratectomy retreatment after LASIK. Neira- Zalentein W , et al. J Refractive Surg 2008 Sep;24(7):710-2   2 Photorefractive keratectomy with 0.02% Mitomycin C for treatment of residual refractive errors after LASIK. Srinivasan S,Drake A, Herzig S. J Refractive Surg 2008 Jan;24(1):S64-7 3  Surface ablation after laser in situ keratomileusis: retreatment on the flap. Beerthuizen JJ, Siebelt E . J Cataract Refractive Surg 2007 Aug;33(8):1376-80