Posterior corneal elevation changes after small incision lenticule extraction

Abstract Background: To investigate posterior corneal surface (PCS) elevation changes and influencing factors after SMILE. Methods: A total of 285 patients (559 eyes) were analyzed. The PCS elevation before the operation, 1 day, 1 week and 1 month after the operation were recorded, including cornea apex and the 2 mm, 4 mm, and 6 mm circle. Analyzed the correlation between the changes with age, equivalent spherical refraction, corneal thickness, lenticule thickness, corneal cap thickness, lenticule diameter, residual corneal thickness, corneal cap thickness/corneal thickness, lenticule thickness/corneal thickness and PCS curvature. Results: There were significant differences in the PCS elevation of the center and 2 mm, 4 mm, and 6 mm circles at 1 day, 1 week and 1 month postoperation (P<0.0001) comparing to preoperation. There were no significant changes after 1 day (P>0.05). At the center and 2 mm circle, the PCS moved backward after the operation, which were positively correlated with preoperative values of K1, K2 and Km on the PCS (r>0, P<0.05). At the 4 mm and 6 mm circles, the PCS moved forward after the operation, while it was negatively correlated with the preoperative K1, K2 and Km of the PCS (r<0, P<0.05). There was no other influencing factors. Conclusions: The PCS elevation changed significantly on the first day after SMILE surgery and then stayed stable. Within the safe range, the possibility of PCS expansion after SMILE is rare. SMILE surgery should be carefully selected for patients with excessive or excessively small PCS curvature.