A comparative study of epithelial hyperplasia after PRK: Summit versus VISX in the same patient

Epithelial hyperplasia has been found to occur after photorefractive keratectomy in eyes treated with small (5 mm or less) ablation zone diameters with the Summit laser, but not with large zones (6 mm) with the VISX laser (Gauthier et al. 1995a). The aim of this study was to further investigate the effect of surgical parameters on epithelial hyperplasia by comparing eyes treated with the same zone diameter but two different lasers. We examined 11 subjects who had photorefractive keratectomy for myopia performed with 5 mm ablation zones with the Summit excimer laser in one eye and the VISX 20/20 laser in the fellow eye an average of 21 months previously. Epithelial thickness and corneal topography were measured. The mean epithelial thickness was not statistically different (p = 0.083) between the eyes treated with the Summit (66 +/- 12 microns) and VISX (60 +/- 14 microns) lasers. Postoperative corneal dioptric power showed a similar profile between the two eyes at the edge of the zone, with the VISX-treated corneas being more shallow centrally. There was a trend towards greater epithelial thickness with deeper ablations. This study supports the hypothesis that epithelial hyperplasia is dependent on ablation zone diameter and ablation depth.