Changes in posterior corneal elevation and associated factors following small incision lenticule extraction in patients with high myopia and thin cornea: a prospective randomized clinical study

To investigate the safety and efficacy of SMILE in patients with high myopia and analyzed the factors influencing corneal posterior elevation variation (PCE). This was a prospective, comparative, randomized, clinical study. Patients with a corneal thickness < 530 mu m at the thinnest point of the right eye with a spherical equivalent (SE) <=-3.00D (group A: <=-3.00D, >-6.00D; group B: <=-6.00D, >-10.00D) who underwent SMILE surgery between January 1, 2020, and May 31, 2021 were randomly selected. We compared the difference in postoperative vertex PCE between the two groups and assessed the correlation between PCE variation (triangle PCE) and corneal biomechanical parameters. The preoperative SE was - 4.74 +/- 0.63D and - 7.38 +/- 1.22D in groups A (41 eyes) and B (37 eyes), respectively. PCE was 0.61 +/- 2.07 and 0.16 +/- 2.19 mu m, and triangle PCE was - 0.93 +/- 1.13 and - 1.43 +/- 1.07 mu m in groups A and B, respectively, showing significant differences (P < 0.05). triangle A2L and triangle A2V (r=-0.41, -0.36; P = 0.02, 0.04) were correlated with triangle PCE. Stepwise regression analysis showed that triangle A2L was the predictor variable of triangle PCE (AIC = 0.8, P = 0.02). SMILE surgery is safe and effective for correcting high myopia with a thin cornea. A2L may affect the variation of vertex PCE following SMILE surgery. The higher reduction in A2L indicates less PCE backward displacement.