Effect of Angle of Incidence on Anterior Chamber Angle Metrics From Optical Coherence Tomography. Issue 1 (January 2016) - Pan, Xiaojing
Abstract : Purpose: To evaluate the local variability of anterior chamber angle (ACA) metrics obtained by time domain (TD) and spectral domain (SD) optical coherence tomography (OCT). Materials and Methods: Anterior-segment OCT imaging was performed on 30 normal eyes using Visante TD-OCT and 40 normal eyes using Cirrus SD-OCT. For Visante OCT, a single 16-mm line scan of the inferior angle with 3 slightly different rotations of 265, 270, and 275 degrees was performed. For Cirrus OCT, a 5-line raster of the inferior angle was performed, centering the third scan line at the 6 o'clock position, with 0.25 mm between lines. ACA measurements were taken for angle-opening distance (AOD) and trabecular iris space area (TISA) at 500/750 μm from the scleral spur for Visante OCT and at Schwalbe's line (SL) for Cirrus OCT. Results: For Visante OCT, AOD500 was 0.406 mm (SD=0.143 mm) and TISA500 was 0.139 mm 2 (0.054 mm 2 ). There was no difference in AOD500, AOD750, TISA500, or TISA750 between the 3 scan orientations ( P >0.1 for all comparisons). For Cirrus OCT, AOD500 was 0.850±0.318 mm and TISA500 was 0.325±0.145 mm 2 . No difference was found in SL-AOD and SL-TISA between the 3 scan positions. Conclusions: These findings suggest that small local changes in the position of the OCT line scan spaced up to 1.0 mm apart on Cirrus, or 10-degree apart on Visante, did not significantly alter the inferior ACA metrics in achieving reliable measurements in young healthy eyes. Given the absence of tracking and registration for current anterior-segment OCT instruments, this observation is of relevance for longitudinal and dynamic studies of angle geometry.