Assessment of Circumferential Angle-Closure by the IriseTrabecular Contact Index with Swept-Source Optical Coherence Tomography

Purpose: To evaluate the diagnostic performance of the irisetrabecular contact (ITC) index, a measure of the degree of angle-closure, using swept-source optical coherence tomography (SSOCT, CASIA SS-1000, Tomey Corporation, Nagoya, Japan) in comparison with gonioscopy. Design: Prospective observational study. Participants: A total of 108 normal subjects and 32 subjects with angle-closure. Methods: The SSOCT 3-dimensional angle scans, which obtain radial scans for the entire circumference of the angle, were performed under dark conditions and analyzed using customized software by a single examiner masked to the subjects' clinical details. The ITC index was calculated as a percentage of the angle that was closed on SSOCT images. First-order agreement coefficient (AC1) statistics and area under the receiver operating characteristic curve (AUC) analyses were performed for angle-closure on the basis of the ITC index in comparison with gonioscopy. Main Outcome Measures: Angle-closure on gonioscopy was defined as nonvisibility of posterior trabecular meshwork for at least 2 quadrants. Agreement of the ITC index with gonioscopically defined angle-closure was assessed using the AC1 statistic. Results: Study subjects were predominantly Chinese (95.7%) and female (70.7%), with a mean age of 59.2 (standard deviation, 8.9) years. The median ITC index was 15.24% for gonioscopically open-angle eyes (n 108) and 48.5% for closed-angle eyes (n 32) (P 0.0001). The agreement for angle-closure based on ITC index cutoffs (> 35% and >= 50%) and gonioscopic angle-closure was 0.699 and 0.718, respectively. The AUC for angleclosure detection using the ITC index was 0.83 (95% confidence interval, 0.76-0.89), with an ITC index > 35% having a sensitivity of 71.9% and specificity of 84.3%. Conclusions: The ITC index is a summary measure of the circumferential extent of angle-closure as imaged with SSOCT. The index had moderate agreement and good diagnostic performance for angle-closure with gonioscopy as the reference standard.