In Vivo Assessment of Optic Nerve Head and Peripapillary Vascular Density in Canine Primary Angle-Closure Glaucoma Using OCT Angiography

Glaucoma is an optic neuropathy that is the leading cause of irreversible blindness in humans and dogs. Multifactorial mechanisms of glaucoma include mechanical injury to the retinal and optic nerve (ON) from increased intraocular pressure (IOP), vascular dysregulation, and other biochemical disturbances causing injury to the retinal ganglion cells. This study sought to evaluate the vascular density (VD) of the optic nerve head (ONH) and peripapillary area (PPA) in progressive stages of canine primary angle-closure glaucoma, hypothesizing that the VD would decrease linearly with disease progression. Additionally, secondary aims were to compare the change in VD to previously reported structural measurements of the retina and ONH. Dogs were enrolled after complete ophthalmic examination and assigned to pre-disposed, early glaucoma, or late glaucoma groups based on IOP and vision status. Age- and breed-matched controls were recruited. Optical coherence tomography (OCT), OCT-angiography (OCT-A), and confocal scanning laser ophthalmoscopy images were acquired and processed for comparison. VD of the ONH was significantly decreased in the early glaucoma (44.91 ± 4.1%, p = 0.037) and late glaucoma (28.76 ± 10.0%, p < 0.001) stages compared to controls (59.34 ± 9.9%). All other OCT and OCT-A measurements were only significantly different in the late glaucoma stages with no detectable differences in earlier points of disease. OCT and OCT-A are valuable tools in understanding structural and vascular changes of the ONH and retina in canine glaucoma. In canine primary angle-closure glaucoma, VD may decrease at a faster rate than retinal thinning.