Validity and Repeatability of Anterior Chamber Depth Measurements With Pentacam and Orbscan

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Abstract
The purpose of this study was to determine the validity and repeatability of anterior chamber depth (ACD) measurements obtained with a novel rotating Scheimpflug camera (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) to scanning slit topography (Orbscan; Bausch & Lomb, Rochester, NY). ACD in 60 healthy eyes was measured twice by two independent observers with each modality in random order. A total of eight measurements was performed on each eye. The mean differences between measurements, between observers, and between modalities were calculated, and 95% limits of agreement (LoA) were given as mean ± 1.96 * standard deviation (SD) of the mean. The mean ACD values as determined with the different modalities (± SD) were 3.18 ± 0.38 mm for Pentacam imaging and 3.23 ± 0.40 for Orbscan. The mean difference between the two modalities was 0.047 mm (LoA: 0.176 to -0.081 mm). Within each modality, the limits of agreement of the differences between individual measurements and between different observers were within 0.073 mm or 4% of total ACD. The total variance in the observed data was 0.145. The variance resulting from interindividual differences in ACD was 85%, as a result of the two different modalities 15%, as a result of different observers 0.007%, and as a result of different measurements 0.007%. In the assessment of normal eyes, the differences of ACD values measured with Orbscan and Pentacam were within clinically acceptable levels, and inter- and intraobserver variability was considerably below clinically significant levels. Thus, these two modalities can be regarded as interchangeable.

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