A COMPARATIVE-STUDY OF EPITHELIAL HYPERPLASIA AFTER PRK - SUMMIT VERSUS VISX IN THE SAME PATIENT

Epithelial hyperplasia has been found to occur after photorefractive k eratectomy in eyes treated with small (5 mm or less) ablation zone dia meters 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 furt her investigate the effect of surgical parameters on epithelial hyperp lasia by comparing eyes treated with the same zone diameter but two di fferent lasers. We examined 11 subjects who had photorefractive kerate ctomy for myopia performed with 5 mm ablation zones with the Summit ex cimer laser in one eye and the VISX 20/20 laser in the fellow eye an a verage of 21 months previously. Epithelial thickness and corneal topog raphy were measured. The mean epithelial thickness was not statistical ly different (p = 0.083) between the eyes treated with the Summit (66 +/- 12 mu m) and VISX (60 +/- 14 mu m) lasers. Postoperative corneal d ioptric power showed a similar profile between the two eyes at the edg e of the zone, with the VISX-treated corneas being more shallow centra lly, There was a trend towards greater epithelial thickness with deepe r ablations, This study supports the hypothesis that epithelial hyperp lasia is dependent on ablation zone diameter and ablation depth.