OPTIC NERVE HEAD VESSEL DENSITY DECREASES IN NATURALLY OCCURRING CANINE ANGLE CLOSURE GLAUCOMA

Abstract

Purpose : The pathophysiologic mechanisms of glaucoma are multifactorial, including hypotheses of primary vascular dysregulation. Naturally occurring glaucoma in canines, while mostly representing angle-closure glaucoma (ACG), has a great role as an accelerated comparative model in disease progression. Optical coherence tomography angiography (OCT-A) is a validated tool to explore optic nerve head (ONH) vascular changes. We hypothesized that vessel density (VD) of the ONH would significantly decrease as the disease naturally progresses in canine glaucoma, even in the earliest clinical stages.

Methods : In a prospective, observational cohort study and with owner consent, dogs were enrolled and eyes were assigned to one of the following groups: (1) predisposed (n=6), (2) visual with history of elevated intraocular pressure (IOP, n=4), blind with history of elevated IOP (n=2), and normal controls (n=4). Patients were immobilized, and OCT-A images were collected at the ONH. Images were manually segmented in the Heidelberg Eye Explorer software, and en-face images were analyzed using ImageJ software. The VDs (%) were calculated for each image, and the groups averaged and compared using ANOVA with Bonferroni adjustments.

Results : The mean ± SD of ONH VDs (%) were 61.1±9.7 for controls, 56.4±13.4 for predisposed eyes, 43.3±6.8 for visual glaucomatous eyes, and 21.6±0.1 for blind glaucomatous eyes. Average VD was significantly lower in blind glaucomatous eyes when compared to both predisposed eyes and controls (p=0.03 and p=0.01, respectively).

Conclusions : OCT-A is a feasible method of assessing ONH VD in dogs. Detectable changes were present in severe disease stages. Smaller differences in VD in early stages of glaucoma were noted but did not reach statistical significance. Larger sample sizes, more sensitive vision assessments, and longitudinal data are warranted as considerations for further studies to better characterize the pathophysiology of naturally occurring canine ACG.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.