Animals are usually presented with high-pressure glaucoma because intraocular pressure (IOP) >40–60 mmHg results in clinical signs of buphthalmia, mydriasis, corneal edema, episcleral venous congestion, and variable ocular pain. The underlying glaucoma may be either open or narrow-closed angle, and either acute or chronic. Dog breeds most often affected with primary glaucoma include the American Cocker Spaniel, Basset Hound, Chow Chow, Akita, Chinese Shar-Pei, Norwegian Elkhound, and Samoyed. In cats, glaucoma is often associated with anterior uveitis, whereas in horses the risk factors are age >10 yr old, anterior uveitis, and breed (Appaloosa). Although globe enlargement (buphthalmia) is detected fairly early in dogs, buphthalmia in horses and cats is often missed until the glaucoma has progressed.
Diagnosis depends on clinical signs and accurate tonometry. The Tono-Pen® and TonoVet® applanation tonometers are the most versatile. Gonioscopy and other diagnostic methods are used to evaluate the anterior chamber angle and the posterior segment, including the optic nerve head.
The goals of therapy are to rapidly lower IOP and to preserve as much vision as possible. Immediate referral to a veterinary ophthalmologist is often helpful. Short-term treatment includes mannitol (1–2 g/kg, IV), topical β-blockers and carbonic anhydrase inhibitors, systemic carbonic anhydrase inhibitors, and either prostaglandin analogues or miotics (pilocarpine or demecarium). The beneficial effects of the topical medications are not usually apparent until IOP is <30 mmHg. If mannitol treatment does not lower IOP within 2–4 hr, anterior chamber paracentesis under general anesthesia may be attempted. Longterm therapy usually includes topical and systemic ocular hypotensive medications, laser cyclophotocoagulation, cyclocryotherapy, and anterior chamber shunts.