Comparison of higher-order aberration and optical quality after Epi-LASIK and LASIK for myopia

Background Epipolis laser in keratomileusis (Epi-LASIK) and laser in situ keratomileusis (LASIK) are two main surgical techniques for myopia in refractive surgery at present. However, the visual outcome and optical quality after the two procedures are not clear. We conducted the current prospective study to compare ocular higher-order aberrations and evaluate optical quality after Epi-LASIK and LASIK. Methods Sixty-two eyes were included. Thirty-two eyes were treated using Epi-LASIK and thirty eyes using LASIK. Best-corrected visual acuity, uncorrected visual acuity, manifest refraction, and wavefront aberrations were measured and analyzed preoperatively and 4–6 months postoperatively. Wavefront aberrations were measured by Wavescan (VISX, Santa Clara, CA, USA) using a Hartmann–Shack sensor. Results The mean changes in RMS for the 5th order (S5) were 0.022±0.009 ìm and 0.050±0.010 ìm, which was significantly smaller in the Epi-LASIK group than in the LASIK group for a 6-mm pupil (P=0.048, analysis of covariance). The mean changes in C5 .1and C5 5 were significantly smaller in the Epi-LASIK group than in the LASIK group at both 3-mm and 6-mm pupil sizes (P=0.027, 0.045 and 0.024, 0.027, analysis of covariance). Also, the changes in the contribution of coma-like and spherical-like aberration at 6-mm pupil size were statistically significantly different after both procedures (P=0.000, randomized block design analysis of covariance). Conclusions Both Epi-LASIK and LASIK show their own characteristics in increased higher-order aberration at smaller and larger pupil sizes, and may create different effects on optical quality for photopic (smaller pupil) and scotopic conditions (larger pupil). We speculate that the visual performance in the Epi-LASIK group may be better than in the LASIK group for the larger pupil size.