Anterior Chamber Angle Imaging with Swept-Source Optical Coherence Tomography: An Investigation on Variability of Angle Measurement

Purpose.: To evaluate the reproducibility of anterior chamber angle measurements obtained by swept-source optical coherence tomography (OCT) and to identify factors associated with its measurement variability. Methods.: One eye from each of 30 healthy subjects was randomly selected for anterior segment OCT imaging (Casia SS-1000 OCT; Tomey, Nagoya, Japan) in three separate visits within a week. The angle opening distance (AOD), the trabecular iris space area (TISA), and the trabecular-iris angle (TIA) at the superior (90°), nasal (0°), inferior (270°), and temporal (180°) angles were measured. The intraobserver and interobserver reproducibility coefficient (RC) and intraclass correlation coefficient (ICC) were calculated. Generalized linear latent and mixed modeling was used to examine the association between the variance of angle measurements and each of the following: angle width, pupil diameter, pupil diameter variance, iris thickness, iris thickness variance, axial length, anterior chamber depth, scan location, scleral spur visibility, and age. Results.: The intervisit, intraobserver RCs ranged between 0.140 mm and 0.252 mm for AOD, 0.050 mm2 and 0.090 mm2 for TISA, and 7.7° and 9.5° for TIA, and the interobserver RCs were between 0.103 mm and 0.187 mm, 0.049 mm2 and 0.101 mm2, and 8.5° and 13.7°, respectively. The ICCs were all ≥0.83. Increased iris thickness, increased iris thickness variance, angle measured at the superior and inferior quadrants, increased angle width, and long axial length were associated with increased variance of angle measurements. Conclusions.: Although the swept-source OCT had high reproducibility for angle measurement, differences in iris thickness, angle width, measurement location, and axial length may influence its variability.