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

PurposeThe 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. MethodsA total of 30 eyes of 30 patients were included. The mean age was 31.28.4years. 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 reliabilityof CASIA and TMS-5 measurements including central corneal thickness (CCT) and thinnest corneal thickness (TCT), keratometry at steep (Ks)andflat (Kf) axes, average keratometry (Avg K), cylinder, and, best-fit spheres (BFS) of the anterior and posterior corneal surfaces were evaluated. ResultsThere 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 (p0.002); scaling differences between CASIA and TMS-5 were also found in CCT and TCT (p0.002). Both machines illustrated adequate reliability. Intraclass correlation coefficients (ICC) 0.952 was recorded for all parameters measured with CASIA and ICC0.914 was recorded for all parameters on TMS-5. CASIA showed significantly higher ICCs in CCT and TCT, and posterior corneal BFS (p<0.001). ConclusionsThis 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.