ROLE OF EPITHELIAL HYPERPLASIA IN REGRESSION FOLLOWING PHOTOREFRACTIVE KERATECTOMY

Aim-To determine the relation between epithelial hyperplasia and regre ssion of effect after photorefractive keratectomy (PRK). Methods-Seven ty unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes serve d as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was perfor med. Results-The epithelium was 21% thicker in the treated eye (p<0.00 01). The relation between refractive regression and epithelial hyperpl asia was significant (r=0.41; p<0.001). Conclusions-Epithelial hyperpl asia after PRK correlated with the myopic shift (including hyperopia r eduction) after treatment with the Summit laser. A model is proposed s uggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 mu m of epithelial hyper plasia contributing each dioptre of regression.