Primary Open Angle Glaucoma

What is primary open angle glaucoma?

Glaucoma is a condition in which the pressure inside the eye (intraocular pressure) rises above the normal range, damaging the optic nerve and retina over time. In primary open angle glaucoma (POAG), this pressure rise occurs despite the drainage angle of the eye appearing structurally normal — which distinguishes it from primary closed angle glaucoma, where the drainage angle is physically obstructed.

POAG is inherited and bilateral, though it often presents initially in one eye. The pressure rise is typically slow and gradual, and crucially, the early stages of the disease cause no obvious pain or visual disturbance that the owner would notice. By the time clinical signs become apparent — globe enlargement, vision loss, lens subluxation — significant and irreversible damage has usually already occurred. This silent onset makes routine screening especially important in affected breeds.

Breeds affected

POAG is currently certified under the BVA scheme in the Petit Basset Griffon Vendeen, Basset Hound, and Shar Pei. In the Shar Pei, the same genetic mutation can cause either POAG or primary lens luxation, or both conditions in the same dog.

DNA testing

A DNA test is available for POAG in the affected breeds. The test identifies whether a dog is genetically clear, a carrier, or affected. Because POAG has a silent onset and may not be detectable by clinical examination until the disease is established, DNA testing is a particularly valuable tool for this condition — allowing breeders to identify affected and carrier dogs before any clinical signs develop.

DNA testing and clinical examination under the BVA scheme are complementary. The BVA examination includes tonometry, which can detect elevated intraocular pressure even in dogs that appear clinically normal, providing an additional check beyond the DNA result.

What the examination involves

The BVA POAG examination consists of a general ophthalmoscopic examination of the globe followed by tonometry — measurement of the intraocular pressure using a handheld contact tonometer. A drop of local anaesthetic is applied to the eye before the tonometer is placed gently on the corneal surface. The procedure takes only a few seconds per eye and is well tolerated by most dogs.

Unlike the routine BVA eye examination, POAG testing does not require pupil dilation, so there is no period of light sensitivity after the appointment. The examination is charged at the standard BVA POAG fee, separate from the routine eye examination fee.

When to test

Annual examination from 3 years of age is recommended for breeding dogs of affected breeds. Because the condition can remain subclinical for some time after onset, regular annual testing gives the best chance of detecting pressure elevation before significant damage occurs.