Therapy Comparison between SMILE and Off-Flap Epi-LASIK

Abstract

Objective: To compare one-year clinical outcomes between small incision lenticular extraction (SMILE) and off-flap epipolis laser in situ keratomileusis (Epi-LASIK) for myopia. Methods: In this retrospective case-control study, choosing from Nanjing General Hospital of PLA between March 2013 and August 2014, 103 eyes of 52 patients underwent SMILE, and 86 eyes of 43 patients underwent off-flap Epi-LASIK. Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), residual astigmatism, and spherical equivalent (SE) were evaluated preoperatively, at 1 day, 1 week, at 1, 3, and 6 months, and at 1 year postoperatively. Contrast sensitivity (CS), modulation transfer function (MTF), and wavefront aberrations were evaluated at 1 year postoperatively. Data were analyzed using repeated measures analysis of variance, independent-samples t-tests, and Chi-square tests. Results: At 1 day and 1 week after surgery, the UCVA for the SMILE group was significantly better than for the Epi-LASIK group (t=5.065, 5.994, respectively, P<0.001 for both); however for all other follow-up times, there were no significant differences in the UCVA between the two groups. At 1 year postoperatively, there was no significant difference in the frequency of eyes SE within ±0.5 diopter (D) or within ±1.0 D between the two groups respectively. However, the frequency with which the SMILE group attained a cylindrical refractive error within ±0.5 D was clearly higher than for the Epi-LASIK group (χ2=10.734, P=0.001). The CS with glare at low spatial frequency [3 and 6 cycles per degree (cpd)] in the SMILE group was significantly higher than for the Epi-LASIK group (t=4.106, 3.848, P<0.001). However, there were no significant differences in CS at other spatial frequencies, with or without glare between the two groups. Total order aberrations, lower-order aberrations, higher-order aberrations, spherical aberrations, coma, trefoil aberrations, and MTFs at all spatial frequencies with 4.0-mm pupils were not significantly different between the two groups. However with 6.0-mm pupils, higher-order aberrations and spherical aberrations of the SMILE group were significantly lower than in the Epi-LASIK group (t=3.881, 6.843, P<0.001 each). There were no significant differences in the other aberrations between the two groups. The MTFs were significantly higher in the SMILE group than in the Epi-LASIK group with 6-mm pupils at low and high spatial frequency (5, 20, 25, 30 cpd) (t=3.272, P=0.001; t=2.926, P=0.004; t=3.280, P=0.001; t=3.975, P<0.001 respectively). There were no significant differences in the MTFs at residual spatial frequency between the two groups. Conclusions: Both SMILE and off-flap Epi-LASIK are safe, efficient, stable, and predictable for the treatment of myopia. However, SMILE had better correction of astigmatic error, and with 6.0-mm pupils, SMILE had better visual quality than off-flap Epi-LASIK. Key words: small incision lenticule extraction; laser in situ keratomileusis; contrast sensitivity; modulation transfer function; aberration