Predictive factors for efficacy and safety in refractive surgery for myopia.

PURPOSE:To evaluate the predictive factors for safety and efficacy in laser refractive surgery for myopia. SETTING:A singular refractive surgery center, at a University-affiliated tertiary medical center. DESIGN:Retrospective cohort study. METHODS:Study population-A total 8,775 eyes having laser refractive laser procedures for myopia (in4,623 patients). Observation procedures-Using a prospective database of refractive procedures performed over the span of 13 years, variables such as gender, age, type of surgery, date of surgery, pre-operative corneal thickness and Spherical Equivalent (SEQ) were evaluated. Main outcome measures-Proportion of patients with Safety index higher than 0.85 and Efficacy index higher than 0.80. RESULTS:91.9% and 86.0% of all evaluated eyes were above the safety and efficacy cut-off levels, respectively. Younger age was significantly correlated with safety and efficacy indices above the cut-off levels (p<0.001). Male gender was significantly correlated with efficacy above the cut-off level (p<0.001). Myopic eyes with lower SEQ were associated with both safety (p = 0.002) and efficacy (p<0.001) indices above the cut-offs. The surgical procedure was found to significantly affect the outcome only using univariate analysis: Safety was higher in Photorefractive Keratectomy (PRK), while Efficacy was higher in Laser Assisted In Situ Keratomileusis (LASIK) (p<0.001, respectively) but no difference was found using multivariate analysis. Safety index above the cut-off level increased over the years (p