To compare the astigmatism induced surgically (SIA) by spherical hyperopic laser in situ keratomileusis (H-LASIK) versus myopic laser in situ keratomileusis (M-LASIK) in nonastigmatic eyes.Methods:
A retrospective study of patients who underwent LASIK surgery between 2005 and 2014 at the Care-Vision Laser Center, Israel. We calculated the mean absolute SIA and performed risk factor analysis for induced astigmatism. Differences between H-LASIK and M-LASIK were analyzed.Results:
Eyes of 3877 patients who underwent M-LASIK and of 549 patients who underwent H-LASIK were nonastigmatic preoperatively and received a nonastigmatic treatment. Three months after surgery, hyperopic treatment induced more SIA (0.49 ± 0.48 D) than did myopic treatment (0.36 ± 0.4 D) (P < 0.001). In the H-LASIK group, the risk factors for induced astigmatism of >0.5 D were a higher preoperative refractive error (P = 0.003) and larger optical zone (7 vs. 6 mm). In the M-LASIK group, eyes with SIA >0.5 D tended to have steeper corneas preoperatively (43.8 ± 1.5 vs. 43.6 ± 1.4 D; P = 0.001), a higher spherical equivalent (−3.43 ± 1.53 Vs. −3.07 ± 1.45 P < 0.001), and smaller treatment zones (6 vs. 7 mm). In H-LASIK, the mean induced astigmatic axis was at 74.6 degrees.Conclusions:
There was a consistent trend toward more SIA in H-LASIK and in higher refractive error correction. In H-LASIK larger optical zones induce more SIA and in M-LASIK smaller ones caused it.