Primary glaucoma is a painful and blinding disease associated with high pressure inside the eye. It is an inherited condition that can come in two forms: primary open angle glaucoma (POAG) and primary closed angle glaucoma (PCAG). Some breeds are known to be at risk of both forms of glaucoma. In both forms, glaucoma results from reduced drainage of fluid from the eye, causing a build-up of pressure which, in turn, leads to pain and blindness. For closed angle glaucoma, a screening technique called gonioscopy (either as part of, or independently of a normal clinical eye exam) can identify dogs at risk.