FACTORS AFFECTING EPITHELIAL HYPERPLASIA AFTER PHOTOREFRACTIVE KERATECTOMY

Purpose: To determine the effect of patient age, postoperative time, a blation zone diameter and depth, attempted correction, and corneal top ography on postoperative corneal epithelial thickness after photorefra ctive keratectomy (PRK).Setting: Private clinic and university hospita l, Stockholm, Sweden. Methods: This retrospective, unmasked study comp rised 136 myopic patients treated unilaterally with PRK. Seventy eyes had been treated with the Summit excimer laser 27 months +/- 7 (SD) ea rlier using ablation zone diameters of 4.1 to 5.0 mm. Sixty-six eyes h ad been treated with the VISX excimer laser 6 +/- 3 months earlier usi ng a 6.0 mm zone diameter. The untreated fellow eyes served as control s. Epithelial thickness was measured at a standardized central corneal area with a modified optical pachymeter, and corneal topography was d etermined using computerized videokeratoscopy. Results: In the Summit group, the epithelial layer in the PRK eyes was 12.0 mu m (21%) thicke r than in the control eyes (P<.001; 95% confidence interval [CI] 9.35 to 14.3 mu m). This thickness differential correlated significantly wi th increased ablation depth and attempted correction. In the VISX grou p, the epithelium in the treated eyes was 7.0 mu m (7%) thinner (P=.00 09; 95% CI-1.9 to -6.7 mu m) and thickness did not correlate with abla tion depth or attempted correction. There was no correlation between e pithelial hyperplasia and patient age or postoperative followup. With the laser groups combined, epithelial hyperplasia was greater with sma ller zone sizes and a greater rate of change in power at the edge of t he ablation zone. Conclusion: The factors associated with an increase in epithelial thickness were small ablation zones, greater attempted c orrections, and deeper ablations. Larger,smoother ablation profiles ma y result in less epithelial hyperplasia.