Repeatability and agreement of a Scheimpflug–Placido tomography and a Partial Coherence Interferometer in keratoconus and normal eyes

Abstract PURPOSE To assess the repeatability and agreement of anterior segment measurements obtained using a partial coherence interferometry − based optical biometry device (AL − Scan) and a combined Scheimpflug − Placido disc system corneal topography device (Sirius) in keratoconic and normal eyes. METHODS Central corneal thickness (CCT), anterior chamber depth (ACD), white-to-white distance (WTW), and keratometry values were measured in keratoconic and normal eyes using AL − Scan and Sirius. The agreement, repeatability, and reliability of the measurements were assessed. RESULTS The study included a total of 82 keratoconus patients (82 eyes) and 100 healthy subjects (100 eyes). The mean CCT and the mean ACD values of Sirius were significantly higher than those of AL − Scan in both groups (p  0.05). In keratometric comparisons between devices, there was mostly no significant difference in normal eyes, whereas almost all of them were significantly different in keratoconic eyes. Reliability was excellent in all parameters for both devices (intra-class-correlation [ICC] > 0.9). Repeatability was excellent in all parameters for all devices (coefficient-of-variation [CoV] < 1%) except for the CCT in keratoconic eyes (CoV) < 3%). CONCLUSIONS Both the AL − Scan and the Sirius are devices providing highly repeatable and reliable measurements, not only in healthy eyes but also in keratoconus. However, the agreement between these devices in eyes with keratoconus is very poor for parameters other than WTW.