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P. S. Kollbaum, M. E. Jansen, C. M. Riley; Repeatability of Orbscan Elevation Measurements in Keratoconic and Normal Eyes. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4964.
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Clinicians often utilize anterior and posterior elevation data obtained with the ORBSCAN to characterize and detect keratoconic (KC) disease. The repeatability of these measures in eyes with KC is not well described, potentially limiting the interpretation of longitudinal changes. We aim to determine the repeatability of ORBSCAN anterior and posterior elevation measurments in normal and KC eyes.
Three repeated ORBSCAN exams from 40 KC and 20 normal, healthy eyes were acquired in the morning and afternoon on three consecutive days. The clinical diagnosis of KC was based on the presence of biomicroscopic signs. Standard settings were used on the ORBSCAN to determine the maximum anterior and posterior elevations above the best-fit sphere. Within session, within day, and across day reapeatbaility was characterized by Bland-Altman and coefficient of variation (CV) analysis.
The average±std maximum anterior elevation for the KC and normal eyes was 46±31 and 16±4 microns, while the maximum posterior elevation was 98±53 and 32±10 microns, for the KC and normal eyes respectively. The within session CV was 0.15±0.15 and 0.19±0.15 for the maximum anterior elevation value, while it was 0.16±0.15 and 0.19±0.12 for maximum posterior elevation value, for the KC and normal eyes respectively. The within day CV was 0.14±0.17 and 0.21±0.16 for the maximum anterior elevation value, while it was 0.13±0.12 and 0.18±0.09 for maximum posterior elevation value, for the KC and normal eyes respectively. The across day CV was 0.19±0.23 and 0.26±0.24 for the maximum anterior elevation value, while it was 0.15±0.15 and 0.20±0.08 for maximum posterior elevation value, for the KC and normal eyes respectively.
Repeatability of anterior and posterior elevation measurements were similar within a measurement session, within a day, and across days for both normal and KC eyes. Repeatability of anterior and posterior elevation measurements were no worse in eyes with KC compared to normal eyes.
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