Changes in corneal asphericity and spherical aberration after femtosecond laser in situ keratomileusis

Abstract

Purpose The aim of this study was to evaluate the changes in corneal asphericity (Q value) and spherical aberration after femtosecond laser in situ keratomileusis using Scheimpflug imaging.Patients and methods This is a prospective nonrandomized study that included 170 myopic eyes and 30 hyperopic eyes. All patients had wave front-optimized femtosecond laser in situ keratomileusis using the EX-500 and FS200 machines (WaveLight, Alcon). Patients within ±0.50 diopter (D) of plano-refraction 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 (Oculyzer II) preoperatively and 1–3 months postoperatively.Results The mean preoperative Q value was −0.28±0.11 and −0.22±0.15 in myopic and hyperopic eyes, respectively, and became +0.35±0.44 and −0.64±0.31, respectively, postoperatively. The asphericity change was highly correlated with the preoperative spherical equivalent (r2=0.81, P≤0.001). The mean preoperative corneal spherical aberration was +0.21±0.08 µm in the myopic eyes, and +0.36±0.11 µm in the hyperopic eyes and became +0.36±0.17 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<0.001). There was a tendency for the 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 (i.e. positive in myopic and negative in hyperopic eyes). The changes depend on the magnitude of the refractive correction.