Glaucoma in Dogs: A Painful Disease

Glaucoma is a condition characterized by increased pressure within the eye, which causes nerve damage, pain and even blindness.

Certain breeds have quirks in their ocular anatomy, which means they are more at risk of developing glaucoma. These breeds include:

• Basset hound
• American and English Cocker Spaniel
• Flat-coated retriever
• Golden retriever
• Samoyed
• Shar-pei
• Welsh springer spaniel

There are 2 forms of glaucoma: sudden onset and a gradual onset. As the name suggests, the sudden forms come on swiftly, and the quick swelling is very painful. The slower form is less so, with the affected eye slowly becoming visibly larger than its healthy partner. Because the eye has some time to stretch, the slower form is less painful.

Treatment is either medical (regular drops into the eye) or surgical (stents to allow drainage). Unfortunately, glaucoma can be difficult to control and sometimes result in patients going blind in the affected eye.

Symptoms

Pressure slowly building inside the eye causes stretching, and the globe becomes larger than the other eye.

Sometimes the eye is so swollen that the surface (cornea) develops a misty or hazy appearance, which is technically described as “corneal bluing.” This finding happens for reasons other than glaucoma but is always a sign to seek veterinary attention.

Glaucoma is painful, and individuals have their own way of showing discomfort. Some become more withdrawn and refuse to eat, while others’ tempers may become shorter. Commonly, the pet will be lethargic and not keen to exercise or go for walks.

Causes

The eye is basically a globe filled with fluid. This fluid, however, is not like a bucket of water that is never changed. It is constantly drained away and replenished.

In a healthy eye, the fluid is produced and drained at the same rate, keeping everything perfectly balanced (the bucket does not overflow). In glaucoma, though, a problem develops with the drainage part of this equation, where more fluid is produced more quickly than it can leak away, causing the inner pressure to build.

If the “drainage angle” is too narrow, this restricts the flow of fluid, a bit like having a blocked storm drain in heavy rainfall. And sometimes there can be a physical blockage, such as the lens slipping out of place or the iris (the colored part of the eye) becoming so inflamed that it clogs the drainage angle.

Diagnosis

The diagnosis is made by testing the intraocular pressure (IOP).

This is done with an instrument called a tonometer, similar to the device used when you have your own eyes tested by the optometrist.

Normal IOP is between 15 and 25 mmHg. Above this, the animal is suffering from glaucoma. A specialist veterinary ophthalmologist will also look inside the eye to troubleshoot for drainage problems.

Treatment

Sophisticated drugs are available to decrease the production of tear fluid or to improve drainage. Although these drugs work well up to a point, sometimes the glaucoma is so severe that surgery is the better option.

Surgery on the eye is incredibly delicate and best done by a specialist with access to magnification and fine instruments. The operation involves placing a stent (a fine tube) to give the excess intraocular fluid a way to drain.

If the dog has already lost his sight or is in permanent pain, then the kindest option may be to remove the eye and get rid of the discomfort once and for all.

This happy Dachshund lost his eye to glaucoma, but he still loves to play fetch:

Prevention

A veterinary ophthalmologist can assess a pet’s risk of developing glaucoma. Especially if one eye has already developed it, there is evidence that treating the remaining at-risk eye may postpone glaucoma’s onset.

Reference

• Small Animal Ophthalmology. Pfeiffer & Peterson-Jones. 3rd edition. Publisher: W. B. Saunders.

This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.