Reliability and agreement of the central and mid-peripheral corneal thickness measured by a new Scheimpflug based imaging

BACKGROUND: To assess the intra-observer repeatability and inter-observer reproducibility of central corneal thickness (CCT) and mid-peripheral corneal thickness (MPCT) measurements using a new Scheimpflug imaging instrument (Scansys) and compare the agreement with the rotating Scheimpflug corneal tomographer (Pentacam HR). METHODS: The same well-trained operator performed the measuring using the two devices, after which Scansys measurements were repeated by another operator. Both instruments required three consecutive measurements per subject. Corneal thickness measurements were obtained by each instrument, including CCT, thinnest corneal thickness (TCT), pupil corneal thickness (PCT), and MPCT. Test-retest repeatability (TRT), within-subject coefficient of variation (CoV), and intra-class correlation coefficient (ICC) were used to evaluate repeatability and reproducibility. A paired t-test was used to compare the differences between Scansys and Pentacam, and the agreement was compared with Bland-Altman plots. RESULTS: This study enrolled 112 healthy subjects. The CoV were <0.91% and 0.55% for repeatability and reproducibility, respectively. The ICC was close to 1 in all measurements. For intra-observer repeatability in the CT(2mm) region, TRT was <10.30 µm. Moreover, TRT was <15.26 µm within the CT(5mm) region. The paired t-test showed significant differences in all corneal thickness measurements (P<0.001). The central region and CT(2mm) agreement were high, but the largest range of 95% limits of agreement (LoA) appeared in the CT(nasal-5mm). CONCLUSIONS: The new Scheimpflug imaging instrument showed excellent intra-observer repeatability and inter-observer reproducibility for corneal thickness measurements. The agreement analysis suggested that Scansys and Pentacam could be interchangeably used between the central region and CT(2mm), except CT(5mm).