Comparison of corneal measurements in keratoconus using swept-source optical coherence tomography and combined Placido–Scheimpflug imaging

Purpose: The aim of this study was to provide a comprehensive comparison of reliability of corneal topographic measurements in keratoconic eyes using swept-source optical coherence tomography (OCT) and a combined Placido–Scheimpflug imaging. Methods: A total of 30 eyes of 30 patients were included. The mean age was 31.2 ± 8.4 years. Two consecutive topographic measurements were obtained for one eye of each patient using swept-source OCT (CASIA) and combined Placido–Scheimpflug imaging (TMS-5). Test–retest reliability of CASIA and TMS-5 measurements including central corneal thickness (CCT) and thinnest corneal thickness (TCT), keratometry at steep (Ks) and flat (Kf) axes, average keratometry (Avg K), cylinder, and, best-fit spheres (BFS) of the anterior and posterior corneal surfaces were evaluated. Results: There was no systematic or scaling bias in any parameter in both devices. Systematic differences between CASIA and TMS-5 were found in posterior corneal Kf, Avg K and BFS, CCT and TCT (p ≤ 0.002); scaling differences between CASIA and TMS-5 were also found in CCT and TCT (p ≤ 0.002). Both machines illustrated adequate reliability. Intraclass correlation coefficients (ICC) ≥0.952 was recorded for all parameters measured with CASIA and ICC ≥ 0.914 was recorded for all parameters on TMS-5. CASIA showed significantly higher ICCs in CCT and TCT, and posterior corneal BFS (p < 0.001). Conclusions: This study showed significant differences in posterior corneal surface and corneal thickness measurements between swept-source OCT and combined Placido–Scheimpflug imaging in eyes with keratoconus. Swept-source OCT might be preferred over Placido–Scheimpflug imaging owing to better repeatability of measurements.