Early histopathologic changes in the retina and optic nerve in canine primary angle‐closure glaucoma

Abstract

To characterize the morphology of canine globes enucleated 1-5days after the onset of overt clinical disease recognized by the owner. Paraffin-embedded globes from 47 dogs with acute primary angle-closure glaucoma (PACG) and 10 control dogs free of ocular disease were sectioned in the vertical plane sampling the optic nerve. Hematoxylin and eosin (H&E)-stained sections were used to count ganglion cell numbers. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to quantify cell death, and MHCII immunohistochemistry was used to evaluate for antigen-presenting phagocytes in a smaller subset of cases. MHCII-labeled phagocytes were present in the optic nerve and retina within the first 24h of documented glaucoma suggesting an early up-regulation. Globes removed within 1day of overt clinical disease had a mild neutrophilic infiltrate in the retina and optic nerve as well as marked ganglion cell necrosis. By 5days after clinical signs appear, there is a rapid decline in the number of ganglion cells and cell death detected by TUNEL labeling in the outer and inner nuclear layers of the retina, but not the ganglion cell layer. The neuropil of the optic nerve progresses from edema and neutrophilia to malacia. These findings suggest that retinal and optic nerve degeneration in dogs with PACG progresses rapidly to irreversible tissue loss within days of recognizable clinical disease.