Diagnostic analysis of angle-closure using the iris-trabecular contact (ITC) index of CASIA2 swept source anterior segment optical coherence tomography

Purpose: To evaluate the diagnostic performance of the iris-trabecular contact (ITC) index measured with the CASIA2 anterior segment optical coherence tomography (AS-OCT) device, in the determination of angle-closure compared with gonioscopy, and to study the degree of agreement between both methods. Methods: A total of 135 eyes (76 open-angle subjects and 59 patients with gonioscopic angle-closure) underwent ITC analysis (the percentage of angle-closure over the 360° circumference) with the CASIA2 AS-OCT device. Dynamic gonioscopy was performed and angle-closure was defined as non-visibility of the trabecular meshwork in ≥ 2 quadrants. The area under the curve (AUC) of the receiver operating characteristic curve for the ITC index was calculated. Sensitivity, specificity, and positive and negative predictive values were determined for various ITC cut-off points. The degree of agreement between the ITC index and gonioscopy was analyzed. Results: The mean ITC index was 3.5 ± 7.8% for eyes with open angle and 34.1 ± 22.2% for gonioscopic angle-closure cases (p < 0.001). The AUC was 0.88 for an ITC cut-off point ≥ 20%, with sensitivity and specificity values of 93.2% and 83.5%, respectively. The overall agreement between CASIA2 and gonioscopy was 85.2%, with false positive and negative rates of 7.4% each. The ITC index showed a direct strong correlation with the number of quadrants gonioscopically defined as angle-closure (r = 0.68). Conclusions: CASIA2 showed excellent diagnostic performance of the ITC index for the assessment of angle-closure and moderate agreement with gold standard gonioscopy. This promising approach provides precise information on the actual situation of the anterior chamber angle.