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 piano 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 (r(2) = 0.81; P <=.001). The mean corneal spherical aberration was +0.21 +/- 0.08 mu m in myopic eyes and +0.36 +/- 0.11 mu m in hyperopic eyes preoperatively and +0.36 +/- 0.17 mu m and 0.00 +/- 0.29 mu m, respectively, postoperatively. The corneal spherical aberration changes were correlated with the amount of preoperative refractive error (r(2) = 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.