REGRESSION AND ITS MECHANISMS AFTER LASER IN-SITU KERATOMILEUSIS IN MODERATE AND HIGH MYOPIA

Objective: The purpose of the study was to evaluate the degree and mec hanism of regression after laser in situ keratomileusis (LASIK) on mod erate to highly myopic eyes during the first postoperative year, Desig n: A prospective, single-center, clinical trial. Participants: A total of 52 eyes of 38 patients were entered in the study; 47 eyes had comp lete data available at each postoperative visit. Intervention: The int ervention was LASIK using the microkeratome to create an 8.5- to 9.0-m m diameter, 130- to 160-mu m-thick flap. A spherical midstromal multiz one ablation (inner zone, 4.5 mm; outer zone, 5.5-6.0 mm) was then per formed using the Summit OmniMed excimer laser (Summit Technology, Inc, Waltham, MA). The mean preoperative refraction was -14.02 diopters (D ). Retreatment for undercorrection and regression was performed betwee n postoperative months 3 and 6 on 13 eyes. Main Outcome Measures: Mani fest spherical equivalent, mean central corneal power, and central cor neal thickness were the parameters measured. Results: At 3 months, fol low-up data were available on 47 eyes. The mean refractive regression was -1.07 D (7.6%) from the first week to the third month. During the first postoperative year, the mean regression of manifest spherical eq uivalent (MSE), increase in corneal power, and increase in corneal thi ckness were symmetric in magnitude and time course for the 34 eyes tha t did not require retreatment (-0.96 D, +1.03 D, and 15 mu m, respecti vely). Conclusion: Early regression of refractive effect after LASIK a ppears to be a consequence of an increase in corneal thickness associa ted with central corneal steepening. No evidence of progressive cornea l ectasia was observed during the first year of follow-up. Longer foll ow-up is required to confirm these trends.