Comparison of 110- and 145-µm Small-Incision Lenticule Extraction Cap Thickness: A Randomized Contralateral Eye Study

Abstract

Purpose: To investigate the visual, refractive, and biomechanical outcomes of small incision lenticule extraction (SMILE) with two different cap thicknesses.Methods: Thirty-four patients were included in this prospective, randomized, contralateral eye study. Subjects were randomized to receive SMILE surgery with a 110-m cap thickness in one eye and 145-mm cap thickness in the fellow eye. Uncorrected and corrected distance visual acuity, contrast sensitivity (CS), total higherorder aberrations (THOAs) and corneal biomechanical properties were compared 3 months after surgery. Results: Postoperative refractive and visual outcomes, CS andTHOAs were similar between the two groups (P . 0.05 for all parameters). At 3 months postoperatively, there was a significant difference in Corvis ST Biomechanical Index (CBI); stiffness parameter at first applanation (SP A1), and Integrated Radius between the two groups (all P , 0.05). Conclusions:Eyes with thicker SMILE corneal caps showed no advantage regarding visual acuity, CS and THOAs over eyes with thinner caps. However, higher cap thickness may result in better corneal biomechanical properties postoperatively.

Corneal subbasal nerve plexus reinnervation and stromal cell morphology with different cap thicknesses in small incision lenticule extraction

“…This finding is consistent with the corneal biomechanical characteristics anatomically and theoretically. The anterior stroma contributes more to the biomechanical stability of the cornea than the posterior stroma, and a thicker corneal cap could spare more anterior stroma and minimize changes in the biomechanics after SMILE [ 9 , 33 ] although Liang [ 34 ] concluded that there was no significant difference in biomechanics among corneal caps with different thicknesses.…”

“…Therefore, for some patients with thin corneas, the surgeon may choose a thinner cap thickness design rather than a randomized cap thickness in clinical practice. Some contralateral eye studies that adopted a randomized study design pertaining to cap thickness demonstrated that mean CCT should be more than 550 μm preoperatively to ensure the safety of the surgery [ 9 , 11 , 33 ]. Second, it would be a better statistical design that data collected and analyzed from one eye per patient.…”