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

Background: Small incision lenticule extraction (SMILE) is a popular procedure for correcting myopia and myopic astigmatism; however, the cornea thins to varying degrees following SMILE surgery, and its postoperative stability may be affected. We investigated the safety and efficacy of SMILE in patients with high myopia and analyzed the factors influencing corneal posterior elevation variation (PCE). Methods This was a prospective non-randomized clinical study. Patients with a corneal thickness -6.00D; group B: ≤-6.00D, >-10.00D) who underwent SMILE surgery between January 1, 2020, and May 31, 2021. We compared the difference in postoperative vertex PCE between the two groups and assessed the correlation between PCE variation (△PCE) and corneal biomechanical parameters. Results 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 µm, and △PCE was 0.93 ± 1.13 and − 1.43 ± 1.07 µm in groups A and B, respectively, showing significant differences (P < 0.05). △A2L and △A2V (r=-0.41, -0.36; P = 0.02, 0.04) were correlated with △PCE. Stepwise regression analysis showed that △A2L was the predictor variable of △PCE (AIC = 0.8, P = 0.02). Conclusions 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 leads to less PCE backward displacement.