May Pulse Article (PART 11 OF 12, COMMON SMALL ANIMAL GLAUCOMAS)

The glaucomas represent a frustrating group of ophthalmic diseases & a leading cause of blindness, generally associated with the unique (non-primate) aqueous drainage systems as well as the propensity for severe secondary ocular inflammation in the domestic species. Some of the more commonly-encountered presentations are described below;

Congenital glaucoma describes severe malformation of the aqueous drainage tracts, which are both hereditary & congenital.  As a result, affected animals display severe, bilateral, ocular pathology, very early in life (generally within weeks to months). Severe buphthalmous is common. Vision salvage is frequently not possible with procedures of comfort typically indicated.

Primary glaucoma describes pathology associated with a hereditary predisposition for elevated IOP and/or ON degeneration. Although the underlying changes (comprising trabecular meshwork atrophy) generally develop over the course of many years, the presentation of primary glaucoma is typically per-acute, frequently developing within just a few hours as a result of ciliary cleft collapse.

Commonly affected breeds include the Cocker Spaniel, Siberian Husky, Bassett Hound, Bouvier des Flanders, Shiba Inu, Chow Chow & Shar Pei. Effective treatment depends upon prompt identification of symptoms and typically encompasses the rapid lowering of IOP using intravenous mannitol followed by more definitive control using medical and/or surgical management control IOP as well as to combat subsequent optic nerve degeneration. Patients that develop primary glaucoma in one eye, are at significant risk for the subsequent development of similar pathology in their contralateral eye.

Secondary glaucoma describes elevated intraocular pressure associated with underlying ocular and/or systemic disease.  Common causes include lenticular (sub)luxation, severe or chronic uveitis, golden retriever associated uveitis, uveodermatologic syndrome & neoplasia. In addition to IOP-lowering medications/procedures, treatment of secondary glaucoma typically encompasses long term anti-inflammatory therapy.

Feline aqueous humor misdirection syndrome occurs as a result of aqueous accumulation within the vitreous, suspected to arise as a result of abnormalities associated with the anterior vitreous face. Resultant changes include vitreous expansion, anterior displacement of the lens/iris diaphragm, anterior chamber and progressive IOP elevation. Clinical symptoms may include mydriasis, anisocoria, discomfort and visual deficits. Initial management initially comprises medical therapy using topical carbonic anhydrase inhibitors and/or miotic agents. With time, progressive IOP elevation, may dictate surgical intervention in the form of lensectomy, vitrectomy and/or ciliary photocoagulation.

Pigmentary glaucoma describes a pathological elevation in intraocular pressure, which occurs as a result of the proliferation and accumulation of cells containing melanin in the aqueous outflow tracts. Studies support a hereditary etiology.  Symptoms are generally bilateral, although not always symmetrical and encompass the visible accumulation of pigment within the scleral/episcleral, corneal and/or uveal tissues. Commonly affected breeds include the Cairn Terrier, Boxer & Labrador Retriever. Palliative management of affected patients comprises medical and/or surgical treatment of elevated IOP, however slow progression of this disease process is typical.

A syndrome comprising slowly progressive intraocular changes, typically culminating in secondary glaucoma, is well recognized within the Golden Retriever breed (already briefly described in a previous review of conditions affecting the uveal tract). This syndrome has been variably described as “Pigmentary Uveitis”, “Golden Retriever Uveitis” and “Pigmentary & Cystic Glaucoma of Golden Retrievers”. Initial symptoms (comprising ocular redness, anterior pigment dispersion, cataract formation and/or IOP elevation) are frequently noted around middle age and are usually bilateral, although not necessarily symmetrical. Treatment is generally empirical, typically comprising topical and/or systemic anti-inflammatory immune-modulating as well as IOP-lowering agents, however secondary glaucoma is frequently the end-point of this disease.

Dr Esson is a board-certified veterinary ophthalmologist with more than twenty years of clinical experience and multiple areas of interest & expertise. His clinic Veterinary Ophthalmic Consulting is family owned & operated and he takes great pride & pleasure in working closely with his friends and colleagues in the greater Southern California veterinary community.

To find a complete list of ophthalmic eye conditions related to this article, please click here.