In Vivo Identification of the Posttrabecular Aqueous Outflow Pathway Using Swept-Source Optical Coherence Tomography

The purpose of this study was to investigate a novel imaging technique to identify the continuous posttrabecular aqueous outflow pathway from a single B-scan, using swept-source optical coherence tomography (SS-OCT). Three-dimensional volume scans of the temporal or nasal side of the anterior segment area at the limbus were acquired from 11 eyes of 11 healthy subjects, using SS-OCT. The aqueous outflow pathway was identified using an en face OCT image and reconstructed images of the vasculature (vasculature map). Delineation of the whole aqueous outflow pathway in a single B-scan was accomplished by reslicing the volume scan. The posttrabecular aqueous outflow pathway was successfully identified in 10 eyes (90.9%). Combined with a flattening technique, the en face video and vasculature map showed a clear blood stream that could not be observed on a sequential stack of B-scans. In the en face images, the vessels were widely branched in the episclera venous plexus, perpendicularly penetrating the scleral stroma. Vessels running parallel to Schlemm's canal and the collector channels were observed in the deeper region of the sclera. The average longitudinal diameter of the vessel was 29.7 ± 6.6 μm at the episcleral venous plexus, and it was significantly larger than that in the deep scleral aqueous plexus (22.0 ± 4.8 μm; P = 0.0002). The continuous posttrabecular aqueous outflow pathway could be identified from a single B-scan and quantitatively analyzed using SS-OCT with en face imaging and volume scan reslicing.