Anterior chamber angle imaging with swept-source optical coherence tomography: detecting the scleral spur, Schwalbe's Line, and Schlemm's Canal.

Objective

To determine the visibility of the scleral spur (SS), Schwalbe's line (SL), and Schlemm's canal (SC) imaged by a swept-source optical coherence tomographer (OCT).

Methods

One eye from each individual was randomly selected from 30 normal subjects and 30 patients with primary open-angle glaucoma for anterior segment imaging with a swept-source OCT. The angles were imaged with 2 protocols: (1) high-density (HD, a raster of 64 B-scans each with 512 A-scans over 8 mm) and (2) low-density scans (LD, 128 radial scans each with 512 A-scans over 16 mm). The visibility of the angle structures was determined by 2 masked observers and compared among the superior (90 degrees), nasal (0 degrees), inferior (270 degrees), and temporal (180 degrees) quadrants.

Results

The interobserver agreement for assessment of visibility of the angle structures was high with agreement coefficients ranging between 0.769 and 0.987. The SS, SL, and SC were visible by both observers in 95% to 100%, 68% to 98%, and 12% to 42% of a total of 240 (4×60) quadrants in 60 HD images, respectively. The visibility was reduced in LD images (50% to 95%, 0% to 10%, and 0%, respectively). The temporal and nasal quadrants generally had superior visibility of the angle structures than the superior and inferior quadrants.

Conclusions

The SS, SL, and SC could be identified with the swept-source OCT although their visibility varied with the scan location and scan density. The SS was best visualized, followed by the SL and then the SC in the OCT images.