Characteristics Influencing Outcomes of Excimer Laser Photorefractive Keratectomy Peter S. Hers h, MD, I.2 Oliver D. Sche in , MD, MPH,3 Roger Ste ine rt , MD ,4 Summit Photore fra ctive Keratectomy Phase III Study Group* Purpose: To identify preoperative and intraoperative characteristics associated with outcomes of photo refractive keratectomy (PRK). Methods: In the phase III multicenter clinical trials of the Summit Technology exci- mer laser for corrections of 1.5 to 6.0 diopters (0) of myopia, three principal outcomes of PRK on 612 patients were examined: (1) uncorrected visual acuity of 20/40 or better, (2) predictability of refractive outcome within 1.0 0 of attempted correction, and (3) stability of refractive result between 12 and 24 months. Multiple logistic regression was used to test for independent associations of multiple preoperative 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 overcorrection (odds ratio = 1.09, 95% CI = 1.06-1.12), but age was not associated with stability of refraction. Greater attempted correction was associated independently with a decreased likelihood of 20/40 or better uncorrected visual acuity (odds ratio = 2.78 for corrections of 3.5-5.5 0, 95% CI = 1.18-6.75; odds ratio = 4.19 for corrections of :2::5.5 0, 95% CI = 1.66-10.58), with decreased predictability (odds ratio = 1.72 for corrections of 3.5-5.5 0, 95% CI = 1.05-2.85; odds ratio = 2.95 for corrections of :2::5.5 0, 95% CI = 1.65-5.26), and with a reduced likelihood of stability of refraction (odds ratio = 3.46 for corrections of :2::5.0 0, 95% CI = 1.32-9.11). No intraoperative character- istics were associated with any of the outcomes assessed. Conclusions: Using this specific excimer laser system with an optical zone of 4.5 or 5.0 mm, patient age and attempted correction are important preoperative characteristics associated with postoperative uncorrected visual acuity and predictability of PRK. Stability of refraction is strongly associated with attempted correction. Such information may help guide patient selection, 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 should be performed before modifying patient treatments using either a 6.0-mm treatment zone or other laser systems. Ophthalmology 1996; 103: 1962-1969 Originally received: October 30, 1995. Revision accepted: July 23 , 1996. J Wilmer Ophthalmologic Inst it ute , Joh ns Hopkins University School of Medicine, Baltimore. * Members o f t he Summit Photorefractive Keratectomy Phase III Study Group are listed in the Appendix section at the end of this article. I Department of Ophthalmology, UMDNJ·New Jersey Medi cal S chool, Newark. 2 Cornea and Laser Institute, Hackensack University Medical Center, Hackensack, New Jersey. 1962 4 Ophthalmic Consultants of Boston, Boston. Presented in part at th e Ameri can Academy o f Ophthalmology Annual Meeting, Atlanta, OctINov 1995 . Supported in part by a nunrestri cted grant to the Department of Ophth al· mology from Research to Prevent Blindness, Inc, New York, New York, and Summit Technology, Inc, Waltham, Massachusetts.