Evaluation of indices for the assessment and classification of keratoconus based on optical coherence tomography and Scheimpflug technology.

Abstract

Purpose: To compare the parameters and indices of a novel swept-source optical coherence tomography device (SS-OCT, ANTERION) with those of a rotating Scheimpflug camera (RSC)-based tomograph (Pentacam) in normal and keratoconic (KC) eyes.

Methods: This prospective, monocentric, cross-sectional study included individuals with unoperated normal and KC eyes, selecting one eye per subject. Ectasia-specific parameters analysed with the SS-OCT were difference in mean keratometry (K_mean) in the inferior and superior meridians, maximum keratometry value (K_max), elevation of the posterior surface at the thinnest point, screening corneal objective risk of ectasia (SCORE) and thinnest point thickness. With the RSC, parameters determined were Belin/Ambrosio total deviation value (BAD-D), index of height decentration and index of vertical asymmetry. KC classification with the SS-OCT was based on the anterior and posterior radii of curvature and thinnest point thickness according to the ABCD classification of the RSC system.

Results: This study included 117 individuals with healthy eyes and 335 eyes with KC. The indices with the highest diagnostic discriminatory ability between the two cohorts were SCORE, difference of K_mean in the inferior and superior meridians and posterior elevation of the thinnest point (SS-OCT), as well as the index of height decentration, index of vertical asymmetry and BAD-D (RSC). The classifications using SS-OCT defined mild-stage KC as K_max, posterior elevation of the thinnest point and thinnest point thickness as ≤50.9 D, ≤30 and ≥472 μm, respectively. Moderate stage values were 51-55.9 D, 31-69 and 471-438 μm, respectively, while respective advanced stage were ≥56 D, ≥70 and ≤437 μm.

Conclusion: The diagnostic capabilities for both devices were found to be comparable. KC classification using SS-OCT can be independently based on the anterior surface, posterior surface and corneal thickness.