Comparison of Anterior Segment Optical Coherence Tomography and Ultrasound Biomicroscopy in the Assessment of the Anterior Chamber Angle

Abstract

Purpose: : To compare anterior segment optical coherence tomography (AS-OCT) with ultrasound biomicroscopy (UBM) in the assessment of the anterior chamber angle (ACA) using gonioscopy as the reference standard.

Methods: : This was a prospective observational study of 296 phakic subjects who were imaged by a single operator with AS-OCT followed by UBM. In all eyes, the nasal, temporal, superior and inferior quadrants were imaged. Gonioscopy was performed by an independent glaucoma specialist who was masked to the imaging tests. The area under the receiver operating characteristic curve (AUC) was generated to assess the performance of these measurements in detecting eyes with angle closure. Horizontal scans of right eyes were analyzed for the temporal and nasal angle opening distance 500µm from the scleral spur (AOD-500) using the Zhongshan Angle Assessment Program (ZAAP).

Results: : The mean age of the subjects was 56.2 years (range 27 to 91 years) and 129 subjects (43.6%) were male. 259(87.5%) subjects were Chinese, 20 (6.8%) subjects were Malays, 7(2.4%) were Indians and 10(3.3%) were of other races. Overall, there were less gradable UBM images than AS-OCT images (1158 vs. 1182 p<0.001). Scleral spur detectability was greater in UBM images than AS-OCT images (89.4% vs. 73.2%, p<0.001). The sensitivity and specificity for detecting eyes with angle closure for AS-OCT were 84.3% and 50.4% (AUC 0.67) respectively, while that for UBM were 86.2% and 46.7% (AUC 0.66). For eyes with a gonioscopically open angle in all 4 quadrants, AS-OCT identified at least one closed quadrant in 49.6% and UBM in 53.3%. The majority of AOD-500 measurements were in agreement within a 95% confidence interval for the two instruments.

Conclusions: : Using gonioscopy as the reference standard, there was good sensitivity but low specificity for both UBM as well as AS-OCT in detecting eyes with angle closure. The scleral spur was better visualized with UBM. Angle measurements by the 2 instruments showed moderate agreement.

Keywords: anterior segment • outflow: trabecular meshwork • imaging/image analysis: clinical