Corneal asphericity and spherical aberration after refractive surgery

PURPOSE: To evaluate changes in corneal asphericity (Q) and spherical aberrations after refractive surgery using Scheimpflug imaging. SETTING: University of California, San Diego, Shiley Eye Center, La Jolla, California, USA. DESIGN: Cohort study. METHODS: After wavefront-guided laser in situ keratomileusis, patients within ±0.50 diopter of plano and with an uncorrected distance visual acuity of at least 20/20 were evaluated. The Q values and corneal spherical aberration Zernike values were obtained using Scheimpflug imaging preoperatively and 1 to 3 months postoperatively. RESULTS: The study enrolled 177 myopic eyes and 32 hyperopic eyes. The mean Q value was −0.28 ± 0.11 (SD) and −0.22 ± 0.15, respectively, preoperatively and +0.35 ± 0.44 and −0.64 ± 0.31, respectively, postoperatively. The asphericity change was highly correlated with preoperative spherical equivalent (r2 = 0.81; P≤.001). The mean corneal spherical aberration was +0.21 ± 0.08 μm in myopic eyes and +0.36 ± 0.11 μm in hyperopic eyes preoperatively and +0.36 ± 0.17 μm and 0.00 ± 0.29 μm, respectively, postoperatively. The corneal spherical aberration changes were correlated with the amount of preoperative refractive error (r2 = 0.34; P<.001). There was a tendency for Q values and spherical aberrations to become more positive after myopic ablation and more negative after hyperopic ablation. CONCLUSIONS: Myopic and hyperopic corrections induced changes in the Q value and spherical aberrations in opposite directions (ie, positive and negative, respectively). The changes depended on the magnitude of the refractive correction. Financial disclosure: No author has a financial or proprietary interest in any material or method mentioned.