Retinal pigment epithelial damage, breakdown of the blood-retinal barrier, and retinal inflammation in dogs with primary glaucoma.

Objective: This paper aims to determine if abnormalities of the retinal pigment epithelium (RPE) and retinal inflammation occur in primary glaucoma.

Procedure: Twenty-three canine globes with primary glaucoma, goniodysgenesis, and elevated intraocular pressure were evaluated. Sections from 6 control and 23 glaucomatous canine globes were stained with hematoxylin and eosin, Griffonia simplicifolia isolectin B4, or immunohistochemically stained for CD3 or albumin. The retinal sections were evaluated with light microscopy for morphological and immunohistochemical evidence of pigmentary changes and inflammation.

Results: Abnormal pigmented cells including displaced RPE cells and macrophages (identified by lectin binding) were found in the neuroretinas and vitreous bodies of glaucomatous eyes. Other abnormalities included hypertrophy of RPE cells and loss of RPE continuity. Regions of neuroretina with more displaced pigment had fewer remaining neurons. Signs of retinal inflammation found in glaucomatous eyes included infiltration with leukocytes, retinal swelling, and albumin leakage from vessels. Accumulation of perivascular CD3-positive T lymphocytes also occurred in glaucomatous retinas. Chronic glaucomatous retinas had increased pigmentary changes, fewer neutrophils, and less swelling than acute glaucomatous retinas.

Conclusions: Disruption of the RPE, increased permeability of the vascular endothelium, accumulation of inflammatory cells, and retinal swelling or thinning occur in canine primary glaucoma. The displacement of pigment and accumulation of inflammatory cells in the neuroretina suggests that inflammation may be an important contributor to retinal damage.