Filtration patterns in human trabecular meshwork appear segmental over both macro-scale and micro-scale dimensions, with only approximately one-third of the trabecular meshwork actively contributing to outflow. Segmental outflow may limit the efficacy of outflow drugs by preventing delivery to non-filtering trabecular regions that may contribute the most to outflow obstruction in glaucoma.

PURPOSE.To describe morphometric details of the human aqueous humor (AH) outflow microvasculature visualized with 360-degree virtual castings during active AH outflow in cadaver eyes and to compare these structures with corrosion casting studies.METHODS. The conventional AH outflow pathways of donor eyes (n = 7) and eyes in vivo (n = 3) were imaged with spectral-domain optical coherence tomography (SD-OCT) and wide-bandwidth superluminescent diode array during active AH outflow. Digital image contrast was adjusted to isolate AH microvasculature, and images were viewed in a 3D viewer. Additional eyes (n = 3) were perfused with mock AH containing fluorescent tracer microspheres to compare microvasculature patterns. RESULTS.Observations revealed components of the conventional outflow pathway from Schlemm's canal (SC) to the superficial intrascleral venous plexus (ISVP). The superficial ISVP in both our study and corrosion casts were composed of interconnected venules (10-50 lm) forming a hexagonal meshwork. Larger radial arcades (50-100 lm) drained the region nearest SC and converged with larger tortuous vessels (>100 lm). A 360-degree virtual casting closely approximated corrosion casting studies. Tracer studies corroborated our findings. Tracer decorated several larger vessels (50-100 lm) extending posteriorly from the limbus in both raw and contrast-enhanced fluorescence images. Smaller tracer-labeled vessels (30-40 lm) were seen branching between larger vessels and exhibited a similar hexagonal network pattern.CONCLUSIONS. SD-OCT is capable of detailed morphometric analysis of the conventional outflow pathway in vivo or ex vivo with details comparable to corrosion casting techniques. (Invest Ophthalmol Vis Sci. ;

Glaucoma is a leading cause of blindness, and elevated intraocular pressure (IOP) characteristic of glaucoma is caused by increased aqueous humor outflow resistance. Studies have localized the bulk of outflow resistance to particular regions along the outflow pathway — namely, the inner wall endothelium of Schlemm’s canal and its underlying juxtacanalicular tissue (JCT) [1] — but the hydrodynamic details of how aqueous humor flows through these tissues and how these tissues generate outflow resistance are not well understood.