CORNEAL TOPOGRAPHY OF PHASE-III EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY - CHARACTERIZATION AND CLINICAL EFFECTS

Purpose: To define qualitative patterns of corneal topography after ex cimer laser photorefractive keratectomy (PRK), assess changes in patte rns, associations with clinical outcomes, and the accuracy of videoker atography in predicting results, and define quantitatively the optical zone contour. Methods: Computer-assisted videokeratography data obtai ned from 181 patients after PRK was analyzed. Topography patterns at t wo time points were characterized, and associations with clinical outc omes were tested. Power change predicted by topography was compared wi th refractive change, and cross-sectional power contours were analyzed . Results: Seven topography patterns were defined. At 1 year, 58.6% of corneas showed a homogeneous topography, 17.7% showed a toric-with-ax is configuration, 2.8% showed a toric-against-axis configuration, 13.8 % showed an irregularly irregular topography, 2.8% showed a keyhole/se micircular pattern, and 4.4% showed focal topographic variants. No cen tral island patterns were found. Of the maps, 41% changed over time. U ncorrected vision, predictability, and patient satisfaction were best in the homogeneous group. Astigmatism increased in the irregular and t oric-against-axis groups and decreased in the toric-with-axis group. T here was no relation of topography pattern to best-corrected vision or subjective glare/halo. Cross-sectional power profiles showed a homoge neous power change for the central 3 mm with a diminution in correctio n toward the periphery. The topography unit tended to overestimate ref ractive change for corrections of 5 diopters or less and underestimate the change for corrections greater than 5 diopters. Conclusions: Topo graphy patterns after PRK are identifiable, time dependent, and may af fect clinical outcomes. Understanding the actual corneal optical conto ur resulting from PRK may aid in improving both laser techniques and o ptical results in the future.