Abstract
PURPOSE: Segmental trabecular outflow has been observed in various species, and we recently reported segmental uveoscleral outflow in mouse eyes. However, whether this pattern exists in other species remains unclear. This study aimed to investigate segmental uveoscleral outflow and its correlation with trabecular outflow in monkey eyes. METHODS: Five healthy eyes of aged cynomolgus macaques were examined. After anesthesia, a fixed volume of tracer was injected into the anterior chamber and allowed to diffuse for 45 minutes before fixation. The eyes were dissected into 12 radial segments, and images were captured using a confocal microscope. Segments were randomly selected for histological study. Tracer intensity and stromal thickness were measured. RESULTS: Four distinct tracer patterns were observed: (1) low flow in both pathways, (2) high flow (HF) in both, (3) HF in trabecular outflow, and (4) HF in uveoscleral outflow. As trabecular outflow contributed 75% of the total outflow, the "HF in uveoscleral outflow" pattern was the least frequent. Segmental flow patterns were observed in both outflow pathways, including components along the uveoscleral outflow pathway: supraciliary and suprachoroidal spaces, spaces between muscle bundles, and ciliary stroma. A positive correlation was found between tracer intensity along the uveoscleral outflow pathway and stromal thickness. CONCLUSIONS: Uveoscleral outflow is segmental and uncorrelated with trabecular outflow in monkey eyes. It primarily occurs in the ciliary stroma, where it positively correlates with stromal thickness. Future studies in human eyes may inform the optimal placement of drainage devices and drug delivery systems targeting the uveoscleral outflow pathway.