Evaluation of the Long-Term Corneal Biomechanics Following SMILE With Different Residual Stromal Bed Thickness in Rabbits.

Abstract

Purpose: The long-term safety of small-incision lenticule extraction (SMILE) surgery for correcting high myopia with a residual stromal bed thickness (RST) less than 50% of the central corneal thickness (CCT) was investigated from a biomechanical perspective.

Methods: Twelve rabbits were enrolled in this study, in which the right eye underwent SMILE surgery (the corneal cap thickness was one third of the preoperative CCT, approximately 120 µm), and the left eye served as the control. The rabbits were evenly divided into two groups, with the RST of 50% and 30% of the preoperative CCT in each group, respectively. Corneal morphology parameters in vivo and biomechanical properties in vitro were determined at 11 months after SMILE surgery. Moreover, the distribution of displacement and Von Mises stress across the cornea were evaluated using finite element analysis.

Results: At 11 months after SMILE surgery, there was no obvious forward shift in the posterior corneal elevation and no significant increase in the mean keratometry from the posterior corneal surface. The elastic modulus of the RST 30% group increased significantly compared to the control, although no significant differences were found in the creep rate, elongation rate, and equilibrium modulus among all groups. Compared to the control, the displacement was smaller in the RST 30% group, while the maximum stress was obviously higher.

Conclusions: No iatrogenic keratectasia occurred in a rabbit model of high myopic SMILE surgery with an RST of less than 50% of preoperative CCT at 11-month follow-up.

Translational relevance: Our findings could provide valuable insights into the safety of performing SMILE with reduced RST values for high myopia correction and guide SMILE procedures.