Merck Manual

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Professional Version

Glaucoma in Small Animals


Sara M. Thomasy

, DVM, PhD, DACVO, Department of Surgical and Radiological Sciences, School of Veterinary Medicine, and Department of Ophthalmology and Vision Science, School of Medicine, University of California, Davis

Reviewed/Revised Mar 2020 | Modified Nov 2022
Topic Resources

Glaucoma is a degenerative optic neuropathy highly associated with elevated intraocular pressure. It can be primary or secondary to underlying causes such as anterior uveitis, lens luxation, or intraocular neoplasia. Treatment is designed to rapidly reduce the intraocular pressure and address the underlying cause, if present.

Animals with acute glaucoma typically present with:

  • blepharospasm

  • episcleral hyperemia

  • diffuse corneal edema

  • mydriasis

  • lack of vision

Intraocular pressure (IOP) is typically markedly elevated at >40–60 mm Hg. With chronicity, the globe enlarges to become buphthalmic, and secondary lens luxation and Haab's striae or focal breaks in Descemet's membrane can occur.

Dog breeds most often affected with primary angle closure glaucoma include:

  • American Cocker Spaniel

  • Basset Hound

  • Chow Chow

  • Chinese Shar-Pei

  • Samoyed

  • Siberian Husky

Beagles and Norwegian Elkhounds typically have primary open-angle glaucoma due to a mutation in ADAMTS10. In cats and horses, glaucoma is often associated with anterior uveitis, although primary glaucoma can rarely occur in both species.

Diagnosis of Glaucoma in Animals

Diagnosis depends on clinical signs and accurate tonometry. Both applanation and rebound tonometry using the Tono-Pen® or TonoVet® tonometers, respectively, are widely used in veterinary practice. Referral to an ophthalmologist should be considered so that gonioscopy can be performed in the unaffected eye to assess the morphology of the iridocorneal angle and to examine the posterior segment, particularly the optic nerve head.

Treatment of Glaucoma in Animals

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 for the aforementioned additional diagnostic techniques and to institute medical or surgical therapy.

In dogs, short-term treatment includes topical prostaglandin analogs (eg. latanoprost), systemic mannitol (1–2 g/kg, IV), and topical or systemic carbonic anhydrase inhibitors. It is critical to assess lens position before administering a topical prostaglandin analog because the intense miosis that occurs can trap an anteriorly luxated lens and further increase IOP. If vision is absent at initial presentation, the prognosis for return of vision is guarded. Longterm therapy usually includes topical and systemic ocular hypotensive medications.

Surgical options for canine glaucoma such as cyclophotocoagulation with an endolaser or transcleral application of anterior chamber shunts (eg. Ahmed valve) should be considered if vision is present, whereas enucleation, evisceration, or intravitreal gentamicin or cidofovir should be considered if vision is absent.

Oral USP glycerin (1-2 mL/kg) can be prescribed as an emergency treatment for owners to administer to their dogs if signs of glaucoma occur; this medication should not be used in patients with diabetes mellitus. If primary glaucoma has been confirmed in a dog, then demecarium bromide once daily or timolol twice daily with a topical steroid once daily should be instituted to delay the onset of a glaucomatous attack in the remaining eye.

In cats and horses, the options for glaucoma management are more limited and are complicated by the often coincident anterior uveitis. For example, prostaglandin analogs are uncommonly used in these two species because they are ineffective at reducing IOP or they cause ocular irritation or intraocular inflammation. The use of laser cyclophotocoagulation and anterior chamber shunts is less well reported in cats and horses than in dogs so it is more difficult to predict their efficacy. Intravitreal gentamicin is contraindicated in cats because of the risk of malignant ocular tumors and should thus be avoided.

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