Validity and repeatability of anterior chamber depth measurements with Pentacam and Orbscan

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.