THEORETICAL AND CLINICAL EFFECT OF PREOPERATIVE CORNEAL CURVATURE ON EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA

BACKGROUND: Individual clinical and optical variables may influence th e effect of excimer laser photorefractive keratectomy. A theoretical m odel to describe the influence of initial corneal power, astigmatism, and topography on the expected results of photorefractive keratectomy would be useful in identifying those variables that may ultimately imp rove the predictability of the procedure. METHODS: Using a mathematica l analysis based on the change in sagittal depth of the central ablati on zone following photoablation, we predict the effect of initial corn eal curvature on the ultimate outcome of a standardized photorefractiv e keratectomy. Refractive results from the Phase III US Food & Drug Ad ministration clinical trials of photorefractive keratectomy were analy zed to confirm these mathematical predictions. RESULTS: We find that t he initial corneal power, theoretically, is not expected to significan tly affect the refractive change that results from a given ablation. S imilarly, the corneal astigmatism present before photorefractive kerat ectomy is expected to be only minimally altered by a spherical excimer laser treatment. Clinically, there is no detectable difference in pre dictability of the procedure amongst groups stratified by initial mean keratometric power. CONCLUSIONS: Our analysis provides a methodology to predict the optical effects of photorefractive keratectomy upon the cornea and may be applied to a variety of hypothetical clinical setti ngs. The predicted lack of clinical association between initial cornea l curvature and predictability of photorefractive keratectomy is confi rmed.