Primary glaucomas occur in the absence of other eye disease, and are therefore presumed to be genetic in origin.[1] The most common type of glaucoma in dogs is primary angle-closure glaucoma (PACG).[1] The least common type of glaucoma in dogs is primary open-angle glaucoma (POAG), although this is the most common type that affects humans.[1] In the Beagle, POAG is an inherited autosomal recessive trait.[2]