Repeatability and comparability of anterior segment biometry obtained by the Sirius and the Pentacam analyzers

To assess the repeatability and comparability of six anterior segment biometry parameters obtained with a novel Scheimpflug camera with a Placido disc topographer (Sirius) and slit-scanning tomography with a Scheimpflug camera (Pentacam), in a sample of 16 unoperated eyes of healthy subjects. The anterior segment was analyzed by a single examiner using the Sirius and the Pentacam analyzers. Mean simulated keratometry (Sim K), flat and steep axis keratometry (K f and K s ), central and thinnest corneal thicknesses (CCT and TCT), and anterior chamber depth (ACD) measurements were evaluated. Repeatability of three sets of measurements from each device was assessed using the coefficient of variation (CV), within-subject standard deviation, and intraclass correlation coefficient (ICC). Bonferroni-adjusted t-tests, and Bland and Altman plots were used to establish agreement between devices. For both devices the CV of repeated measurements was <0.79 %. The ICC was >0.95 in all measurements except for Sirius K s (ICC = 0.869). For all parameters evaluated, the Pentacam systematically yielded higher values, although differences were statistically significant in only three parameters-0.31 diopters for K s , 10.1 μm for CCT and 12.4 μm for TCT. In the assessment of normal corneas both devices showed overall high repeatability. Although good agreement was found in three parameters (Sim K, K f and ACD) these devices do not seem to be interchangeable for pachymetric determination.