Glaucoma is elevation of intraocular pressure associated with degenerative optic neuropathy. It can be primary or secondary to underlying causes such as anterior uveitis, lens luxation, or intraocular neoplasia. Treatment is designed to rapidly decrease the intraocular pressure and address the underlying cause, if present.
Acute glaucoma is considered an ophthalmological emergency. Elevated intraocular pressure can result from anterior uveitis, lens luxation, or intraocular neoplasia, or it can be due to a primary defect in the iridocorneal drainage angle. In either case, the elevated pressure leads to pain and ultimately to degenerative optic neuropathy.
Animals with acute glaucoma typically develop the following clinical signs:
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 striae or focal breaks in the Descemet membrane can occur (see primary glaucoma image).
Courtesy of Dr. K. Gelatt.
The following dog breeds are those most often affected by primary angle closure glaucoma, whereby the angle suddenly collapses and intraocular pressure rapidly rises:
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 which IOP slowly rises over time. In cats, glaucoma is often associated with anterior uveitis, although primary glaucoma can rarely occur as well.
Diagnosis of Acute Glaucoma in Animals
Diagnosis of glaucoma depends on clinical signs and accurate tonometry. Both applanation and rebound tonometers are widely used in veterinary practice.
Referral to an ophthalmologist should be considered so that gonioscopy and ultrasonographic biomicroscopy can be performed in the unaffected eye to assess the morphology of the iridocorneal angle and ciliary cleft, respectively. It is also important to examine the posterior segment, particularly the optic nerve head, for signs of cupping, which would suggest previous glaucomatous damage.
Treatment of Acute Glaucoma in Animals
The goals of treatment of glaucoma are to rapidly lower IOP and to preserve as much vision as possible. Immediate referral to a veterinary ophthalmologist is often helpful for additional diagnostic techniques and to institute medical or surgical treatment.
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, the prognosis for return of vision is guarded. Longterm treatment 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 should be considered if vision is present, whereas enucleation, evisceration, or intravitreal gentamicin or cidofovir should be considered if vision is absent.
Glycerin (1–2 mL/kg, PO) can be prescribed as an emergency treatment for owners to administer to their dogs if clinical 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 the unaffected eye should be treated with demecarium bromide (1 drop every 24 hours) or timolol (1 drop every 12 hours), in combination with a topical steroid (eg, prednisolone acetate) every 24 hours, to prevent a glaucomatous attack in that eye (1).
In cats, 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 cats because they are ineffective at decreasing IOP or they cause ocular irritation or intraocular inflammation. The use of laser cyclophotocoagulation and anterior chamber shunts is not as well reported in cats as it is 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.
Key Points
Glaucoma is a common cause of irreversible blindness in dogs; therefore, early diagnosis is critical.
Intraocular pressure should be measured in all dogs with ocular pain, corneal edema, or episcleral injection, as long as the cornea or sclera is intact.
In patients with elevated intraocular pressure due to acute glaucoma, aggressive management is necessary to decrease the pressure.
For More Information
Maggio F. Glaucomas. Top Companion Anim Med. 2015;30(3):86-96.
Miller PE, Eaton JS. Medical anti-glaucoma therapy: beyond the drop. Vet Ophthalmol. 2020;24(S1):2-15.
Also see pet health content regarding glaucoma in dogs and in cats, as well as glaucoma as an emergency.
References
Miller PE, Schmidt GM, Vainisi SJ, Swanson JF, Herrmann MK. The efficacy of topical prophylactic antiglaucoma therapy in primary closed angle glaucoma in dogs: a multicenter clinical trial. J Am Anim Hosp Assoc. 2000;36(5):431-438. doi:10.5326/15473317-36-5-431
