Comparison of posterior corneal elevation after SMILE and FS-LASIK in correcting myopia over −9.0 diopters

BACKGROUND: To compare the changes in posterior corneal elevation after small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in correcting myopia over −9 diopters (D). METHODS: In this prospective comparative study, 82 eyes of 82 patients scheduled for refractive correction were recruited. Eyes were randomly assigned to the SMILE group (45 eyes, −10.43±0.92 D) or FS-LASIK group (37 eyes, −10.97±1.37 D). The posterior corneal surface was measured using a Scheimpflug camera (Pentacam, Oculus, Germany) preoperatively and at 1 day, 1 month, and 6 months after surgery. Posterior corneal elevation in the central point and central 4-mm area, and in various optical zones above the best-fit sphere, was analyzed. A P value of less than 0.05 was considered statistically significant. RESULTS: All surgeries were completed successfully. The safety index and efficacy index were 1.20 and 1.00, respectively, in the SMILE group, and was 1.10 and 0.90, respectively, in the FS-LASIK group. No significant difference existed in all analyzed data before and at 6 months after surgery in both the SMILE group and the FS-LASIK group. Changes in posterior corneal elevation after FS-LASIK were greater than after SMILE, with no statistical significance (P≥0.07). In the SMILE group, residual bed thickness was found to be moderately negatively correlated with changes in the elevation in the central area (P≤0.045); whereas it was positively correlated in the peripheral area (P=0.002). CONCLUSIONS: SMILE and FS-LASIK presented stable posterior corneal surface in correction of myopia over −9.0 D at the follow-up visit of 6 months.