Abstract
Purpose :
Segmental trabecular outflow has been observed in various species, and segmental uveoscleral outflow was recently found in mouse eyes by our research group. However, the existence of the segmental flow pattern in uveoscleral outflow and its correlation with trabecular outflow in other species remain unknown. This study investigated the flow pattern along the uveoscleral outflow pathway and its correlation with trabecular outflow in monkey eyes.
Methods :
Intraocular pressure (IOP) was measured in the eyes of five adult female cynomolgus macaques. After administering anesthesia with ketamine (10 mg/kg), a fixed volume of tracer (50 µl) was injected into the anterior chamber. The tracers were allowed to diffuse and reach the outflow systems for 45 minutes, and the eyes were fixed with 4% paraformaldehyde (PFA) in situ. After euthanasia, the eyes were enucleated and immersion-fixed with 4% PFA for 48 hours. The eyes were dissected into 12 radial segments based on clock hours. Images of both sides of each segment were captured by a confocal microscope after nuclear counter-staining and analyzed using ImageJ. The normalized tracer intensity (tracer intensity at different locations/total intensity of each eye) was calculated and compared.
Results :
The average IOP was 19.7±1.9 mmHg. Segmental uveoscleral outflow was observed where the normalized tracer intensity was the highest at 11 o’clock and lowest at 3 o’clock. Concurrently, in the trabecular outflow pathway, the normalized tracer intensity was the highest at 2 o’clock and lowest at 5 o’clock. Overall, a high-flow region was identified at the superior quadrant in the uveoscleral and the nasal quadrant in the trabecular outflow pathway. Both outflows were uncorrelated (p>0.05). Four different tracer patterns were found: 1) Low flow in both outflow pathways (Figure A); 2) High flow in both outflow pathways (Figure B); 3) High flow mainly in the trabecular outflow pathway (Figure C); and 4) High flow mainly in the uveoscleral outflow pathway (Figure D).
Conclusions :
Uveoscleral outflow is segmental and uncorrelated with the segmental flow patterns in the trabecular outflow pathway in monkey eyes, similar to mouse eyes. Future studies of segmental uveoscleral outflow patterns in human eyes will provide a better understanding of the optimal location for the placement of drainage devices and drug delivery systems targeting this pathway.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.