Comparison of effective optical zone after small-incision lenticule extraction and femtosecond laser-assisted laser in situ keratomileusis for myopia

Purpose: To compare the effective optical zone (EOZ) after small-incision lenticule extraction (SMILE) and femtosecond laser- assisted laser in situ keratomileusis (FS-LASIK). Setting: Jinan Mingshui Eye Hospital, Jinan, China. Design: Retrospective case series. Methods: Myopic patients who had small-incision lenticule extraction or FS-LASIK were enrolled in this retrospective study. Effective OZs were measured at 1 week, 1 month, and 3 months postoperatively, using the tangential curvature difference map of the Scheimpflug tomography system. Correlations between the changes in the EOZ and relevant parameters were analyzed 3 months postoperatively. Results: The study comprised 76 patients (76 eyes). The mean EOZs at 1 week, 1 month, and 3 months postoperatively were 5.39 +/- 0.27 mm, 5.33 +/- 0.30 mm, and 5.34 +/- 0.23 mm in the small-incision lenticule extraction group and 5.06 +/- 0.36 mm, 4.98 +/- 0.39 mm, and 5.01 +/- 0.31 mm in the FS-LASIK group, when the programmed OZ was 6.5 mm. The magnitude of decreases in EOZ was significantly smaller in the small-incision lenticule extraction group than in the FS-LASIK group at all timepoints after surgery (P < .01). There were significant correlations between changes in EOZ and corneal asphericity (P < .01). Epithelial thickening was positively correlated with EOZ reduction in the small-incision lenticule extraction group (r = 0.479, P < .01); however, no correlation was found between epithelial thickening and EOZ reduction in the FS-LASIK group (r - = .324, P > .05). Conclusions: Both small-incision lenticule extraction and FS-LASIK resulted in EOZ reduction during correction of myopia. However, small-incision lenticule extraction resulted in less reduction than FS-LASIK and was associated with corneal asphericity changes and epithelial thickening. (C) 2018 Published by Elsevier Inc. on behalf of ASCRS and ESCRS