Response of the cornea for up to four years after photorefractive keratectomy for myopia

PURPOSE: To analyze the long-term corneal topographic changes 4 years after myopic photorefractive keratectomy (PRK). METHODS: This study comprised 15 patients (30 eyes) who had PRK surgery with a scanning-spot excimer laser (Chiron Technolas 217C; Bausch & Lomb, Dornach, Germany) and were followed up to 4 years after surgery. The eyes were subdivided into three groups according to the preoperative spherical equivalent refraction. Corneal topographic maps were obtained for all eyes with a Placido disc topographer. Preoperative and follow-up topographical data were imported into a custom software program, which computed the average composite corneal maps and difference maps for each study group to quantify the anterior corneal changes following laser ablation. The software delineated three concentric zones of the corneal surface to characterize the regional corneal remodeling following the surgery. RESULTS: A significant central corneal steepening (approximately 0.25 D, P <.001) was calculated between the 1- and 4-year postoperative maps in all study groups. A significant steepening (P <.001) of the corneal periphery was also noted for the lower myopic ablations whereas a peripheral flattening (P <.001) was observed for the deeper ablations between 1 and 4 years after surgery. CONCLUSIONS: The anterior corneal surface was observed to remodel for up to 4 years after surface ablation, steepening a mean of approximately 0.25 D.