Corneal Biomechanical Properties after Small Incision Lenticule Extraction Surgery on Thin Cornea.

PURPOSE: To explore the biomechanical changes in thin corneas after the small incision lenticule extraction (SMILE) surgery. METHODS: This prospective survey screened patients scheduled for the SMILE surgery from November 2017 to March 2018. Patients with thin corneas (central corneal thickness [CCT] ≤500 µm) and those with normal corneal thickness (CCT > 500 µm) were enrolled. Corneal biomechanics were examined by the ocular response analyser and Corvis ST, preoperatively and at 1 day, 3 weeks, and 3 months postoperatively. RESULTS: Twenty-seven patients (46 eyes) with mean spherical equivalent of -5.1 ± 1.7 D were assigned to the thin cornea group, and 28 (45 eyes) cases with mean spherical equation of -5.3 ± 1.8 D were assigned to the control group. Safety and efficacy did not differ between the two age- and refraction-matched groups (safety index, 1.15 ± 0.14 vs 1.14 ± 0.17 [P = .7]; efficacy index, 1.11 ± 0.13 vs 1.16 ± 0.22 [P = .2]). All biomechanical parameters changed significantly after SMILE. The thin cornea group showed less decrease in the second applanation time (A2 Time), stiffness parameters at first applanation (SP-A1). Pooling data from two groups, lower CCT was correlated with less A2 Time change (r = 0.37, P < .01) and less SP-A1 change (r = -0.33, P < .01). Less bIOP change was correlated with higher residual stromal thickness index and thicker CCT (P = .003, R2 = 0.12). CONCLUSION: Over a short-term observation period, less corneal biomechanic deterioration may have contributed to the safety of SMILE on thin cornea.