Clinical Efficacy and Posterior Corneal Elevation of Small Incision Lenticule Extraction in High Myopes

Abstract

Objective: To investigate the safety, efficacy, predictability, stability and posterior corneal elevation of small incision lenticule extraction (SMILE) for high myopia. Methods: This study was a descriptive longitudinal study. A retrospective analysis was performed on 37 patients (67 eyes) with high myopia (spherical equivalent, -10.75--6.25 D) who underwent SMILE in the Ophthalmology Department of Xiangya Hospital, Central South University in 2016. Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), refractive error, intraocular pressure (IOP), axial length, and corneal topography were measured preoperatively and postoperatively at 1 day, 1 month, 3 months and 6 months. The data before and after surgery and the influencing factors were analyzed by a generalized estimation equation. Results: The UCVA (LogMAR) of the high myopes was -0.1 (-0.2, 0), the effective index was 0.83±0.20, the BCVA (LogMAR) was -0.2 (-0.2, -0.2), and the safety index was 1.03±0.16 at 6 months after SMILE. The degree of myopia increased gradually from 1 month to 6 months postoperatively. The refractive error was -0.25 (-0.50, 0) D and regression was -0.25 (-0.50, 0) D at 6 months after SMILE. UCVA was positively correlated with age, refractive error and regression and was negatively correlated with age after surgery. The difference value of the posterior corneal surface was 0.030±0.006 mm before and 0.046±0.012 mm 6 months after surgery, which was lower than that in the first month, and was not statistically different at 3 months. Difference and Δdifference at 6 months were positively correlated with mPTA (modified percent tissue altered). Conclusions: This study demonstrates SMILE to be a safe, effective, predictable and stable procedure for the treatment of high myopia, with a slight myopic regression at 6 months after surgery, especially in elders. The posterior corneal surface shifts forward postoperatively and partially recovers after 3 months; the amounts are associated with mPTA. Key words: small incision lenticule extraction; high myopia; posterior corneal surface