A new 3-Dimensional (3D) method for assessment of the anterior chamber angle

Purpose To evaluate the reproducibility and accuracy of the 3-dimensional (3D) corneal and anterior segment optical coherence tomography (CAS-OCT) in assessing the anterior chamber (AC) angle Methods Fifty participants with bilateral occludable angles and 50 participants with bilateral open angles from the Chinese American Eye Study underwent gonioscopy and 3D AC assessment using CAS-OCT (Tomey, Nagoya, Japan). One eye of each participant was randomly selected for analysis. Using the “3D Angle Analysis” mode (Figure 1), a total of 256 cross-sectional images of AC were collected under dark adapted conditions. After the graders manually identified sclera spurs on 16 sample slices, the customized analytic software will export average values of AC parameters and volume parameters based on all 256 slices using splicing technique and calculus (Figure 2). AC parameters include angle opening distance (AOD), trabecular meshwork space area (TISA), trabecular meshwork space volume (TISV), anterior chamber volume (ACV) and iris volume (IV). Thirty participants underwent the first scan by technician 1 and a repeated scan by technician 2 for image acquisition reproducibility analysis. All images were analyzed by grader 1 twice then by grader 2 for intra- and inter-grader repeatability analysis. Intraclass correlation coefficient (ICC) was calculated for all the repeatability. Agreement between OCT and gonioscopy angle grading was evaluated by Spearman correlation coefficient (SCC). Results Presented in the sequence of AOD, TISA, TISV, ACV and IV. The image acquisition reproducibility was 0.89, 0.95, 0.95, 0.99, and 0.92, respectively. For open angle group, the intra-grader repeatability was 0.88, 0.95, 0.95, 0.99, 0.95 and inter-grader repeatability was 0.78, 0.81, 0.83, 0.86, 0.85, respectively. For occludable angle group, intra-grader repeatability was 0.75, 0.79, 0.82, 0.97, 0.79 and inter-grader repeatability was 0.70, 0.71, 0.74, 0.83, 0.73, respectively. Average AOD/TISA derived from 3D AS models showed better correlation with gonioscopy grading (SCC: 0.77/0.70) than those from 2D single scans (SCC: 0.73/0.65). Conclusions With the aid of custom software, 3D CAS-OCT is a promising AS assessment method by providing convenient, repeatable and accurate measurements.