Semiautomated SD-OCT Measurements of Corneal Sublayer Thickness in Normal and Post-SMILE Eyes

Abstract

Purpose: 

To test the reliability of a novel algorithm for measuring corneal epithelial thickness (ET) and stromal thickness of normal eyes and post–small incision lenticule extraction (SMILE) corneas with spectral-domain optical coherence tomography.

Methods: 

In this prospective observational study, a customized semiautomated software algorithm was developed and applied to measure corneal ET and stromal thickness along the horizontal corneal meridian. Measurements were performed by 2 examiners in a randomized fashion on a sample of 40 eyes with previous SMILE for treatment of myopia and a control group composed of 40 normal eyes. The intrauser repeatability and interuser reproducibility were analyzed by calculating typical indices including the coefficient of variation and intraclass correlation coefficient. Corneal sublayer thickness profiles were compared between normal and post-SMILE eyes.

Results: 

In both groups, coefficients of variation were 3.2% or lower and intraclass correlation coefficients were 0.929 or higher indicating excellent reliability of the measurement method. Central ET was on an average 6 μm greater in post-SMILE corneas (58.8 ± 5.4 μm) compared with normal eyes (52.8 ± 4.0 μm), with P < 0.01. Also, there was greater interindividual variability in ET in post-SMILE corneas and their horizontal epithelial profile seemed to show a lenticular appearance.

Conclusions: 

Highly favorable indices of measurement reliability were achieved for this novel method of measuring corneal sublayer pachymetry not only in normal eyes but also in eyes with previous SMILE. The corneal ET profile was significantly altered in post-SMILE eyes compared with normal corneas.