Evaluation Of Posterior Corneal Curvature Changes After Small Incision Lenticule Extraction

Correct estimation of the corneal dioptric power will result in post-keratorefractive procedure emmetropia. The change in diotoric power is noted in both the anterior and posterior surfaces of the cornea post kreatorefractive procedures. The change in the posterior surface is largely unaccounted during the calculations targeting emmetropia. The study aimed to evaluate the changes occurring in the posterior surface of the cornea in eyes undergoing SMILE for correction of a mild, moderate, and high degree of myopia. It also aimed to evaluate the correlation between such changes and residual MRSE.

A single centre prospective trial to observe changes following SMILE for a follow-up period of 3 months to study the changes in posterior corneal curvature in participants undergoing SMILE for myopia.

Minimum sample size was 225 eyes and with the institutional drop-out rate of follow-up taken into account, 280 eyes were recruited in the study. All the participants underwent preoperative evaluation and routine corneal topography with Orbscan IIz. A standard operative protocol for SMILE was maintained throughout the study period. The corneal topography with Orbscan IIz was done at 1-week, 1-month and 3-month follow-up. The posterior corneal curvature changes were assessed. Shapiro-Wilk test for the normalcy of data, ANOVA analysis for baseline comparison between the groups, paired t-test for comparing preoperative and postoperative changes in posterior corneal power changes were employed.

248 eyes of 124 participants were analysed while assigned into mild, moderate and high group based on the amount of MRSE. The posterior keratometric readings increased significantly among all the groups at the postoperative 1-week follow-up with p-value less than 0.001 in all three groups, which did not change significantly at 1-month and 3-month. Increase in the negative dioptric power of posterior surface is significantly related with higher residual MRSE in the mild myopia group (r=0.301, p=0.007), while correlation was not significant in moderate and high myopia group.

This study systematically evaluates the changes in a mild, moderate, and high degree of myopia, and its correlation with the residual MRSE. The is a positive significant correlation between MRSE and an increase in negative dioptric power which may have an impact on the calculations for target emmetropia.