A Comparison of Induced Astigmatism in Conventional and Wavefront–Guided Laser in situ Keratomileusis

Abstract

Abstract: : Purpose: To compare the magnitude and axis of surgically induced astigmatism (SIA) after conventional and wavefront–guided (WG) laser in situ keratomileusis (LASIK). Methods: In this single–center retrospective study, two laser platforms, VISX S4 and LADAR 4000, were used to deliver conventional and custom treatments for a total of 208 eyes (52 consecutive eyes in each group). The primary outcome measure was manifest refraction, which was evaluated preoperatively and at 1 week, 1 month, and 3 months postoperatively. The magnitude and axis of the SIA were calculated using vector analysis. The Student t–test was used to compare the magnitude of the SIA while the axial shift was compared using the chi–square test. Results: The mean preoperative manifest cylinder was 0.74 +/– 0.34 D for conventional VISX, and 0.60 +/– 0.51 D for WG–VISX (P=0.1), and 0.74 +/– 0.56 D for conventional LADAR and 0.62 +/– 0.37 D for WG–LADAR (P=0.12). The mean values for the SIA at 3 months were 0.04 +/– 0.26 D for conventional VISX and 0.08 +/– 0.34 D for WG–VISX (P=0.56), and 0.04 +/– 0.26 D for conventional LADAR and 0.06 +/– 0.24 D for WG–LADAR (P=0.63). The mean SIA axis of rotation at 3 months was 4 degrees for conventional VISX and 17 degrees for WG–VISX, and 7 degrees for conventional LADAR and 9 degrees for WG–LADAR. The differences were not statistically significant. Conclusions: Wavefront–guided ablation tends to increase the magnitude and axis of surgically induced astigmatism more than conventional post LASIK though not to a statistically significant degree. Care should be emphasized in registration, centration, and flap alignment to minimize SIA in WG–LASIK.

Keywords: astigmatism • refractive surgery: LASIK