Evaluation of different residual stromal bed thickness on long-term in vivo corneal biomechanics following SMILE in rabbits.

Abstract

This study aims to evaluate the long-term biomechanical safety of SMILE in vivo, focusing on the continuous changes in corneal biomechanics over an extended period for the correction of high myopia with a residual stromal bed thickness (RST) less than 50 % of the preoperative CCT. Twelve rabbits were included in this study. The right eye of each rabbit underwent SMILE surgery, with the corneal cap thickness at one-third of the preoperative CCT, approximately 120 μm, while the left eye served as the control. The rabbits were evenly divided into two groups (n = 6 per group), with the RST of 50 % and 30 % of the preoperative CCT in each group, respectively. Corneal biomechanical and morphological parameters were assessed using Corvis ST and Pentacam HR at preoperative, 1, 3, and 11 months postoperatively. In the RST 50 % group, the Stress-Strain Index (SSI) decreased significantly at 1 month, while Deflection Amplitude Maximum (DA max) and DA ratio (2 mm) decreased at 11 months. In the RST 30 % group, the Horizontal Curvature Ratio (HCR) increased at 1 month, the Inflection Ratio (IR) decreased at 1 month, and HCR further increased at 3 months. At 3 months, the RST 30 % group exhibited higher biomechanical stability than the RST 50 % group. At 11 months, both groups showed no significant differences in biomechanical or morphological parameters compared to controls, indicating a return to normal corneal resistance to deformation. Postoperative CCT decreased initially but gradually increased, with the RST 30 % group showing a greater increase between 1 and 3 months. No evidence of iatrogenic keratectasia was observed in either group. The in vivo corneal biomechanical properties exhibited sustained changes throughout the follow-up period. Moreover, no iatrogenic keratectasia occurred in a rabbit model of high myopic SMILE surgery with RST of less than 50 % of preoperative CCT at 11-month follow-up.