Glaucoma in Dogs and Cats

Laurie Anne Walden, DVM

Photo by freddy dendoktoor on publicdomainpictures.net

Glaucoma is caused by increased pressure inside the eye. It can be painful and often causes blindness even with treatment. Acute glaucoma is an emergency, so dogs and cats with any signs of eye discomfort or vision loss need to be examined by a veterinarian right away.
 
Causes
Pressure inside the eye, or intraocular pressure, is controlled by a balance of fluid production and fluid drainage. In dogs and cats, glaucoma results from decreased fluid drainage.
 
Fluid drains out of the eye mostly at the angle where the clear cornea and the colored iris meet inside the eye. This area, called the iridocorneal angle, contains a sieve-like network of tiny ligaments and tissues that regulate fluid flow. Anything that interferes with the iridocorneal angle can cause glaucoma.
 
Primary vs secondary glaucoma
Primary glaucoma is caused by an inherited problem with the structure or function of the iridocorneal angle. Some of the dog breeds at increased risk are cocker spaniels, beagles, basset hounds, Siberian huskies, and Samoyeds. Primary glaucoma is a progressive disease. Affected dogs need lifelong treatment, and the chance they will eventually become blind is high. Primary glaucoma is very rare in cats.
 
Secondary glaucoma is caused by another eye disease (like uveitis, lens luxation, cataract, or cancer of the eye) that results in physical blockage of the iridocorneal angle.
 
Acute vs chronic glaucoma
Acute glaucoma is an increase in intraocular pressure for less than a day. Chronic glaucoma is an increase in intraocular pressure for longer than a day. The best chance for saving vision is to start treatment during the acute stage. However, the early signs of glaucoma can be subtle or mistaken for another eye problem, so glaucoma often isn’t diagnosed until it’s chronic.
 
Signs
Glaucoma causes the same signs of eye discomfort as other eye disorders. Animals with glaucoma can also have subtle behavior changes caused by eye pain. The signs usually start in only 1 eye but might not be noticed until chronic glaucoma has affected both eyes. These are some of the signs of glaucoma:

• Redness of the white part of the eye
• Squinting
• Clear, watery discharge from the eye
• Cloudy eye
• Enlarged eyeball (with chronic glaucoma)
• Vision loss (might not be obvious if only 1 eye is affected)
• Rubbing the eye
• Head shyness
• Reduced activity level
• Decreased appetite

 
Diagnosis
A high intraocular pressure measurement confirms the diagnosis of glaucoma. Devices used to measure intraocular pressure in animals are similar to those used in humans. Animals with glaucoma benefit from referral to a veterinary ophthalmologist to evaluate the iridocorneal angle and assess the risk of glaucoma in the other eye. Animals with secondary glaucoma usually need additional tests.
 
Treatment
Glaucoma is managed, not cured. The goals of treatment are to prevent pain, preserve vision as long as possible, and delay glaucoma onset in the other eye. Animals with acute glaucoma need emergency treatment to quickly reduce intraocular pressure, and they are typically hospitalized for intraocular pressure monitoring and pain management. Some patients need surgical treatment. Dogs with primary glaucoma need ongoing treatment with eye drops, oral medication, or both.
 
Once an eye with glaucoma is irreversibly blind and painful, the kindest option is surgery to remove the eye. Animals tend to do well with this surgery and feel much better after the eye is removed.
 
Prognosis
For dogs with primary glaucoma, the long-term prognosis for vision is typically poor. However, early diagnosis and treatment can help these dogs stay comfortable and able to see for some time. Blind animals can have a very good quality of life with care and environmental management.   
 
If secondary glaucoma is identified and treated quickly and the cause can be eliminated, the prognosis for retaining vision is better than with primary glaucoma.

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