The District Vet

Glaucoma

293

Glaucoma isn’t only a disease of people. Cats and dogs can have elevated eye pressure, too!

Many people have heard of glaucoma, but what is it? Let’s talk in simple terms. The eye is a hollow organ with a window at the front and it is filled with fluid. The back of the eye has an organ which detects light, similar to a digital camera. This is the retina. In order to keep the eye in its round shape, the eye has a moderately increased pressure, similar to why a balloon stays inflated. This fluid is called the aqueous humor.

Glaucoma is when the pressure in the eye is too high, like an over-inflated balloon. While the eye will not pop (unless there are complicating factors), this elevated pressure can damage sensitive parts of the eye, leading to pain and blindness.

Aqueous humor in the eye circulates: it is constantly produced and reabsorbed at the same rate when everything is working as it should. Problems arise when there is decreased absorption of the fluid or if there is a structure in the eye blocking its ability to flow and drain.

The most common sign seen with glaucoma is an “angry” eye;  there is redness of the white of the eye, excessive blinking, differing sized pupils, swollen eye(s), a color change to the clear portion of the eye (cornea), sudden blindness, signs of pain or discomfort, and other symptoms.

Elevated pressures cause numerous problems, with some, but usually not all of these clinical issues being present. The excessive pressure may slowly kill the cells in the retina which detect light and send messages to the brain. This leads to decreased sight and eventual blindness if too much of the retina dies. In cases where the eye swells and becomes larger, it can tear the delicate strands of fibers which hold the lens in place. This can lead to the lens popping out of place, and even lead to further glaucoma, specially if the lens migrates toward the font of the eye, acting like a plug.

Glaucoma is diagnosed by measuring the pressure. The simplest method involves assessing the firmness of the cornea, similar to poking a balloon and seeing how much give it has. This is called tonometry and is easily measured in the hospital. When measuring eye pressure, it is important to get a number of measurements and to check both eyes. The pressure can be artificially elevated in a stressed pet, one who is being held too tightly, or affected by sedatives. Low pressure can occur if there is an infection in the eye or some types of inflammation.

Elevated eye pressure and glaucoma is seen most commonly in purebred dogs and cats, especially any dog with a smooshed face (boxer, pug, Boston), cocker spaniel, Shiba Inu, shih tzu, Scottish terrier, Cairn terrier, beagle, and in Himalayan cats. But any dog or cat can develop glaucoma.

Treatment depends upon the cause of the elevated pressure, but regardless, the goal is to lower the eye pressure back to normal. Surgery can be performed using lasers. The laser destroys some of the tissue that produces aqueous humor, therefore allowing the eye more time to absorb the fluid. This is the most common surgical procedure. Placing a stent may also be done, but this is far less common. Topical medications aimed at either creating production of fluid or increasing the outflow of fluid can be tried.

Dan Teich, DVM, Medical Director, District Veterinary Hospital. www.districtvet.com