Variation of Lenticule Thickness for SMILE in Low Myopia

PURPOSE: To report the impact of increasing minimum lenticule thickness on the safety and efficacy of small incision lenticule extraction (SMILE) in low myopia up to −3.50 diopters (D). METHODS: SMILE was performed in 76 eyes of 76 patients. Thirty-eight eyes of 38 patients with low myopia were prospectively operated on with a programmed minimum lenticule thickness of 15 to 30 μ m (thicker lenticule group). Thirty-five eyes suitable for analysis were then retrospectively matched by spherical equivalent to 35 eyes operated on with a minimum standard setting of 10 μ m (standard thickness group), as provided in the database of the SMILE Eyes Clinic Linz, Linz, Austria. Comparison of outcomes was performed with the Standard Graphs for Reporting Refractive Surgery and by analysis of higher order aberrations as provided by Scheimpflug imaging. RESULTS: Apart from lenticule thickness, there was no significant difference in preoperative baseline or treatment parameters between both groups. Mean minimum lenticule thickness differed significantly (standard thickness = 10 ± 0 μ m; thicker lenticule = 20 ± 5 μ m; P < .0001). This also translated into a significant difference in maximum lenticule thickness (standard thickness: 54 ± 11 μ m; thicker lenticule: 62 ± 8 μ m; P = .0002). Mean SEQ preoperatively was −2.25 ± 0.51 (standard thickness) and −2.24 ± 0.46 (thicker lenticule) D, respectively, and changed to −0.11 ± 0.50 (standard thickness) and +0.01 ± 0.36 (thicker lenticule) D postoperatively ( P < .0001 for both comparisons). Uncorrected postoperative visual acuity was −0.08 ± 0.35 (standard thickness) versus −0.10 ± 0.09 (thicker lenticule) logMAR ( P = .706). After SMILE, the thicker lenticule group showed better safety (1.20 vs 1.08; P = .025) and efficacy (1.14 vs 0.96; P = .011) indices, translating into more eyes within ±0.50 D from target (91% vs 77%) and with at least 0.0 logMAR visual acuity (97% vs 86%), and fewer eyes losing one (3% vs 17%) and two (0% vs 3%) lines. CONCLUSIONS: Increasing minimum lenticule border thickness seems to improve the safety and efficacy of SMILE in low myopia. [ J Refract Surg. 2018;34(7):453–459.]