Influence of Cap Thickness on Corneal Curvature and Corneal Biomechanics After SMILE: A Prospective, Contralateral Eye Study

PURPOSE: To evaluate the impact of cap thickness for small incision lenticule extraction (SMILE) on changes in corneal curvature and biomechanics. METHODS: One hundred eyes (50 patients) were enrolled in this prospective contralateral eye study. The difference in manifest refraction spherical equivalent (MRSE) in the same patient was less than 0.50 diopters. SMILE was performed with a randomized cap thickness of 110 µm in one eye and 140 µm in the other eye. MRSE, uncorrected distance visual acuity (UDVA), and corneal curvature and biomechanics were evaluated. The anterior and posterior surfaces of the corneal curvature (mean keratometry [Km] values 2, 4, and 6 mm from the pupil center) were measured by Pentacam HR (Oculus Optikgeräte, Wetzlar, Germany) and changes in corneal biomechanics at 6 months postoperatively by Scheimpflug technology. RESULTS: There was no significant between-group difference in UDVA or MRSE postoperatively. Postoperative changes in Km at the anterior surface (ΔKm-ant) in the 4-mm zone were significantly higher in the 110-µm group than in the 140-µm group at 1 day and 1, 3, and 6 months postoperatively ( P = .043, .045, .003, and .049, respectively); at 3 months, the ΔKm-ant in the 6-mm zone was higher in the 110-µm group ( P = .035). The changes in second appla-nation time, deformation amplitude, and integrated radius were significantly less in the 110-µm group ( P = .031, .049, and < .001, respectively). CONCLUSIONS: A thicker corneal cap caused less change in anterior surface curvature after SMILE for moderate or low myopia, with no significant difference in UDVA and MRSE. [ J Refract Surg . 2020;36(2):82–88.]