Development and validation of methods to visualize conventional aqueous outflow pathways in canine primary angle...

Area of Science:

• Veterinary Ophthalmology
• Glaucoma Research
• Ocular Anatomy

Background:

• Primary angle closure glaucoma (PACG) is common in dogs and difficult to treat.
• Persistent elevated intraocular pressure (IOP) in PACG may stem from issues in the post-trabecular aqueous humor outflow pathway.
• Aqueous angiography (AA) and optical coherence tomography (OCT) are imaging techniques that can visualize ocular structures.

Purpose of the Study:

• To investigate abnormalities in the post-trabecular aqueous outflow pathway in canine PACG.
• To evaluate the utility of AA and OCT in identifying these abnormalities.
• To correlate imaging findings with histopathology.

Main Methods:

• Ex vivo anterior segment OCT and AA were performed on 19 enucleated canine eyes (10 normal, 9 with PACG).
• Eyes were infused with fluorescent tracer, and OCT scans were acquired.
• Histopathology was performed on cryosections to identify vascular structures.

Main Results:

• Normal canine eyes exhibited circumferential limbal AA signal, correlating with visible scleral lumens on OCT.
• Canine PACG eyes showed minimal to no AA signal, with absent or flattened scleral lumens on OCT.
• Histopathology revealed collapsed intra-scleral vascular profiles in PACG eyes.

Conclusions:

• Distal aqueous outflow channels are not identifiable by AA in canine PACG eyes.
• OCT and histopathology show collapsed intra-scleral vascular profiles in PACG.
• These findings suggest impaired post-trabecular aqueous outflow contributes to PACG in dogs.