CHARACTERISTICS INFLUENCING OUTCOMES OF EXCIMER-LASER PHOTOREFRACTIVEKERATECTOMY

Purpose: To identify preoperative and intraoperative characteristics a ssociated with outcomes of photorefractive keratectomy (PRK). Methods: In the phase III multicenter clinical trials of the Summit Technology excimer laser for corrections of 1.5 to 6.0 diopters (D) of myopia, t hree principal outcomes of PRK on 612 patients were examined: (1) unco rrected visual acuity of 20/40 or better, (2) predictability of refrac tive outcome within 1.0 D of attempted correction, and (3) stability o f refractive result between 12 and 24 months. Multiple logistic regres sion was used to test for independent associations of multiple preoper ative and intraoperative characteristics with each of these outcomes. Results: Older age was independently associated with lesser likelihood of achieving 20/40 or better uncorrected visual acuity (odds ratio = 1.08 per incremental year of age, 95% confidence interval [CI] = 1.04- 1.12) and with decreased predictability, specifically with overcorrect ion (odds ratio = 1.09, 95% CI = 1.06-1.12), but age was not associate d with stability of refraction. Greater attempted correction was assoc iated independently with a decreased likelihood of 20/40 or better unc orrected visual acuity (odds ratio = 2.78 for corrections of 3.5-5.5 D , 95% CI = 1.18-6.75; odds ratio = 4.19 for corrections of greater tha n or equal to 5.5 D, 95% CI = 1.66-10.58), with decreased predictabili ty (odds ratio = 1.72 for corrections of 3.5-5.5 D, 95% CI = 1.05-2.85 ; odds ratio = 2.95 for corrections of greater than or equal to 5.5 D, 95% CI = 1.65-5.26), and with a reduced likelihood of stability of re fraction (odds ratio = 3.46 for corrections of greater than or equal t o 5.0 D, 95% CI = 1.32-9.11). No intraoperative characteristics were a ssociated with any of the outcomes assessed. Conclusions: Using this s pecific excimer laser system with an optical zone of 4.5 or 5.0 mm, pa tient age and attempted correction are important preoperative characte ristics associated with postoperative uncorrected visual acuity and pr edictability of PRK. Stability of refraction is strongly associated wi th attempted correction. Such information may help guide patient selec tion, determine timing of fellow eye treatment, and suggest changes in the laser treatment algorithm for individual patients. Although these findings may be representative of PRK in general, similar analyses sh ould be performed before modifying patient treatments using either a 6 .0-mm treatment zone or other laser systems.