Orbscan Global Pachymetry: Analysis of Repeated Measures

PURPOSE: The Orbscan II is a hybrid slit-scanning and Placido disc corneal topographer capable mapping global pachymetry over a 10-mm corneal diameter. In this study, the repeatability of the Orbscan global pachymetry was determined. METHODS: Five consecutive Orbscan examinations were performed on one eye of 20 healthy volunteers by one examiner in one session. Mean, standard deviation, range of readings, and coefficient of variance were calculated for the central, thinnest point and global pachymetry. RESULTS: Orbscan repeatability for the central pachymetry was 3.62 microm (95% confidence interval [CI], 0.57-6.66) with a coefficient of variance of 0.67% (95% CI, 0.09-1.25) and intraclass correlation coefficient (ICC) of 0.978 (95% CI, 0.959-0.990). Thinnest point pachymetry had a repeatability of 4.25 microm (95% CI, 1.19-7.31) with a coefficient of variance of 0.80% (95% CI, 0.19-1.42) and ICC of 0.973 (95% CI, 0.950-0.988). Global pachymetry had a coefficient of variance <1.5% in the central 4 mm and <<2.5% across the entire cornea. Global pachymetry showed an area of greatest repeatability (<< +/- 5 microm) within a central 3.0-mm horizontal and 4.0-mm vertical diameter. DISCUSSION: Orbscan is capable of giving repeatable pachymetry readings that are comparable to the ultrasound pachymeter within the central and thinnest point of the cornea. There is a gradual loss of repeatability toward the peripheral cornea possibly as a result of a lack of overlapping data points.