title: Theoretical and clinical effect of preoperative corneal curvature on excimer laser photorefractive keratectomy for myopia.
abstract: BACKGROUND
  Individual clinical and optical variables may influence the effect of excimer laser photorefractive keratectomy. A theoretical model 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 improve the predictability of the procedure.
  
  
  METHODS
  Using a mathematical analysis based on the change in sagittal depth of the central ablation zone following photoablation, we predict the effect of initial corneal curvature on the ultimate outcome of a standardized photorefractive keratectomy. Refractive results from the Phase III US Food & Drug Administration clinical trials of photorefractive keratectomy were analyzed to confirm these mathematical predictions.
  
  
  RESULTS
  We find that the initial corneal power, theoretically, is not expected to significantly affect the refractive change that results from a given ablation. Similarly, the corneal astigmatism present before photorefractive keratectomy is expected to be only minimally altered by a spherical excimer laser treatment. Clinically, there is no detectable difference in predictability 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 settings. The predicted lack of clinical association between initial corneal curvature and predictability of photorefractive keratectomy is confirmed.
authors.affiliation: Center for Lightwave Science and Technology, Fairleigh Dickinson University, Teaneck, NJ.
authors.forename: J W
authors.initials: JW
authors.lastname: Blaker
authors.forename: P S
authors.initials: PS
authors.lastname: Hersh
mesh_terms: D001251:Astigmatism / Q000473:pathology; D003315:Cornea / Q000473:pathology* / Q000601:surgery*; D006801:Humans; D053685:Laser Therapy; D008433:Mathematics; D008962:Models, Theoretical; D009216:Myopia / Q000601:surgery*; D016896:Treatment Outcome