Assessment of measurement repeatability by keratoconus severity using an OCT and Placido-based tomographer.

Abstract

Purpose: Current criteria for assessing keratoconus progression rely heavily on Scheimpflug technology. However, this technology has demonstrated limitations in measurement repeatability, particularly in advanced keratoconus, and it applies a uniform standard across all disease stages. We aim to evaluate the repeatability of diagnostic indices for keratoconus screening using an anterior segment OCT coupled with Placido disc tomographer (MS-39) across different keratoconus stages to establish severity-based thresholds for progression.

Design: Retrospective, multicentre cohort study.

Methods: This retrospective study included 1103 eyes diagnosed with keratoconus, with three scans per eye acquired using the MS-39. The repeatability of curvature, elevation, and thickness indices was assessed using the coefficient of variation (CV%), confidence interval (CI), and coefficient of repeatability (CR). The study analysed the variability of these indices across different stages of keratoconus severity.

Results: The MS-39 demonstrated high repeatability across most indices. Variability increased in advanced stages of keratoconus, particularly in posterior elevation and thickness parameters. For K flat and K steep, CR values remained below 1 D, with the highest CR for K flat being 0.53 up to a keratometry reading of 50 D, and for K steep being 0.74 up to a reading of 56 D. A thinnest point CR below 6 μm was observed for corneas up to 460 μm, while below 420 μm, the CR increased to 10.8 μm.

Conclusion: OCT coupled with Placido disc tomographers offers an overall high repeatability of keratoconus diagnostic indices. Our findings allow us to establish new progression criteria tailored to the severity of the disease.