Effect of larger ablation zone and transition zone on corneal optical aberrations after photorefractive keratectomy

Objective: To evaluate the effects of photorefractive keratectomy on cornea l optical aberrations using a 5.5-mm optical zone and a 7.0-mm transition z one. Methods: Videokeratographs of 72 eyes from 47 patients treated for low to m oderate (1-9 diopters) myopia were obtained at the preoperative and 1-, 3-, 6-, 12-, and 18-month postoperative examinations. The videokeratoscopy dat a files were used to calculate the wavefront variance of the corneas for sm all (3-mm) and large (7-mm) pupils using a previously described method. Results: In general, all optical aberrations decreased postoperatively for 3-mm pupils and increased for 7-mm. pupils compared with preoperative value s. For 3-mm pupils, the 2 common optical aberrations (comalike [S-3] and sp herical-like [S-4]) decreased postoperatively and never returned to preoper ative values. For 7-mm pupils, however, comalike aberrations increased slig htly and spherical-like aberrations increased by nearly an order of magnitu de during the postoperative period. Similarly, for 3-mm pupils, the higher order S-5 and S-6 aberrations decreased throughout the postoperative period , with S-6 values showing an approximately 23-fold reduction at 12 and 18 m onths. For 7-mm pupils, S5 and S6 aberrations increased slightly, more so f or S-5 (approximately 3-fold) than for S-6. Total wavefront aberrations dec reased an average of 2.3 times postoperatively for 3-mm pupils, and increas ed significantly (P < .05) at all postoperative examinations for 7-mm pupil s. Opening the pupil from 3 mm to 7 mm before surgery produced a 14-fold in crease in total aberrations, whereas this same change produced an average 1 13-fold increase after photorefractive keratectomy. Conclusions: Corneal optical aberrations after photorefractive keratectomy with a larger ablation zone and a transition zone are less pronounced and m ore physiologic than those associated with first-generation (5-mm) ablation s with no transition zone. Clinical Relevance: Evaluating the postoperative corneal aberration structu re will help us devise ways to minimize the wavefront aberrations of the ey e through the creation of an ideal corneal first surface, thereby improving visual results for patients undergoing excimer laser ablations for refract ive correction.