Measuring anterior chamber depth with the Orbscan Topography System

Purpose: To assess the reliability of the Orbscan Topography System in measuring anterior chamber depth (ACD). Setting: Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany. Methods: The Orbscan Topography System is a 3-D, scanning slit beam system for analyzing corneal surfaces as well as structures of the anterior segment, e.g., iris, lens. Reflected surface data points are measured in the x, y, and z axes, creating color-coded true surface topography maps. We measured ACD prior to cataract surgery in 56 eyes of 37 patients (mean age 70.4 years + 13.2 [SD]) using the Orbscan system and, as a control, the Grieshaber Biometric System (ultrasound) and the Jager ACD slitlamp measurement system. Results: Mean ACD values measured with the Orbscan system were 3.23 +/- 0.55 mm; ultrasound measurements were 3.27 +/- 0.54 mm and Jager measurements, 3.10 +/- 0.55 mm. The average difference between Orbscan and ultrasound values was 0.04 +/- 0.15 mm. The correlation coefficient between Orbscan and ultrasound was 0.96 (P < .00001) and between Orbscan and Jager, 0.899 (P < .0001). Conclusion: The ACD measurements by the Orbscan system were equivalent to common reference measurements.