Glaucoma in Pets

By: Lorelei Prichard DVM
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Glaucoma is a sight-stealing disease shared by pets and their owners alike. In fact, glaucoma is one of the most important causes of blindness in both humans and dogs. Approximately 3 million Americans have glaucoma, and the prevalence of canine breed-related or primary glaucoma in North America has recently been estimated to be 0.89%. The frequency of secondary glaucoma in cat and dogs is currently unknown.

Glaucoma is a multifactorial disease characterized by an elevation of intraocular pressure (IOP) beyond that which is compatible with the health of the eye. In a healthy eye, clear fluid (known as aqueous humor) is constantly produced behind the iris. This fluid flows then through a microscopic, drainage canal in the front of the eye. The aqueous humor maintains the intraocular pressure and inflates the globe of the eye. If this drainage channel becomes blocked, the pressure inside the eye goes up and often causes damage to the optic nerve and loss of vision.

The diagnosis of glaucoma is based in clinical signs, tonometry and gonioscopy. The tonometer is an instrument utilized to measure the fluid pressure inside the eye. This fluid, or aqueous humor, nourishes the cornea, iris, and lens, and it helps the eye maintain its globular shape. Gonioscopy is utilized to classify the glaucoma as primary or secondary

Glaucoma may be categorized as primary or secondary in nature. Primary glaucoma is not associated with any other ocular disease and has no known predisposing cause. It is generally seen in certain breeds with a hereditary origin, and there are over forty breeds that can develop inherited primary glaucoma. Poodles, Basset hounds, Cocker Spaniels, Beagles, Springer Spaniels and Chow Chows, Huskies, Afghans and Shar-Peis tend to be over-represented. Although breed-related glaucoma is most commonly seen in purebred dogs, it is rare in cats.

Secondary glaucoma results from some event or trauma to the eye. Causes can include lens luxation, trauma, retinal detachment, neoplasia and ocular melanosis (hereditary condition in cairn terriers).

Winking, blinking, and cloudiness in the eye are often the first symptoms an owner notices, but chronic glaucoma often presents as an enlarged, reddened (“bloodshot”) eye. Dilated pupils, a “swollen” edematous eye may be observed, and a change in behavior (hiding, avoiding food) is commonly noticed. The signs of severe pain reduce a few days after onset.

Glaucoma can be seen at any age, but middle-aged dogs, 4-9 years of age and cats over 6 years old are commonly affected. Normal IOP range in the dog and cat is generally considered to be approximately 10-25 mmHg, and pressures above this range should raise suspicion of glaucoma. In general, glaucoma occurs less frequently in the cat than in the dog.

Long-term visual prognosis in canine primary glaucoma is very poor. The prognosis for the secondary glaucoma depends on the underlying disease and its response to treatment. Because our pets can’t speak, glaucoma is often called the “silent thief”, stealing their sight without warning.
“We are excited to have purchased the equipment to perform intraocular pressure testing at Park Place Animal Hospital,” says Jessica Smith, veterinary technician. “An early diagnosis can greatly affect our chances of saving your pet’s vision.”

Detection and early treatment are the keys to preventing vision loss. The goal of the veterinarian is to (1) determine whether the patient has glaucoma, (2) determine if it is primary or secondary, and (3) determine if it is acute or chronic. Once this is established, then a treatment plan can be initiated. Both medical and surgical therapy may be used in glaucomatous patients, and most pets diagnosed with acute glaucoma will be immediately referred to a veterinary ophthalmologist.
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Copyright © 2009 Lorelei Prichard DVM