By Dr. Becker
Today’s topic is glaucoma in pets.
Glaucoma is a condition in which there is increased intraocular pressure within your pet’s eye.
The cells of the eye produce a clear fluid called aqueous humor.
This fluid provides nutrients to tissues inside the eye and also helps maintain the shape of the eye.
Basically it is a fluid-filled ball.
The aqueous humor is fluid inside the eye, whereas tears are fluids that lubricate the outside of the eye (cornea).
The aqueous humor drains through a kind of sieve out of the eye and into the bloodstream.
A good balance of aqueous humor production and drainage is what keeps the pressure inside the eye (intraocular pressure) normal.
If the sieve or ‘drain’ becomes clogged partially or completely, the fluid production continues and the pressure builds up inside the eye.
This is the condition known as glaucoma.
The increasing eye pressure, if left untreated, will cause the eye to enlarge, become misshapen, and ultimately cause irreversible blindness.
Primary and Secondary Glaucoma
In pets, glaucoma is either primary or secondary.
Primary glaucoma is inherited. The condition is very rare in cats, but it occurs in many breeds of dogs, including the cocker spaniel, basset hound, chow, Jack Russell, Shih tzu, and the Siberian husky.
Primary glaucoma typically starts in one eye, but in most cases it will eventually involve both eyes.
Secondary glaucoma occurs when other eye diseases are present that inhibit drainage of the aqueous humor inside the eye. These diseases include inflammation of the eye (called uveitis), advanced cataracts, cancer of the eye, lens displacement, and chronic retinal detachment.
Secondary glaucoma in cats is almost always a result of chronic uveitis.
Needless to say, increasing pressure inside the eye causes pain. The pressure can get much higher in dogs and cats than it does in humans. We can assume this means glaucoma is probably much more painful for pets than it is for you or me.
Primary and Secondary Glaucoma
The pain of glaucoma in pets is most likely felt as a headache, and probably up to migraine status. But as most of you know, it can be difficult to tell when a dog or cat is hurting.
You may notice your pet doesn’t want to play, is irritable, or perhaps his appetite is off. You might also notice your dog rubbing or pawing at his eye or face. Sometimes dogs will rub their faces against furniture or another object in the home, which is another potential symptom. Some pets will have fluttering of the eyelid, squinting, or will even hold their eyes closed.
Another sign is a dilated pupil in the affected eye. Since glaucoma typically strikes one eye at a time, if you notice one pupil is larger than the other, you should suspect glaucoma. If one eye is bulging or looks different to you, it can also be a sign of glaucoma. It’s time to make an appointment with your veterinarian in either of those situations.
Loss of vision is another symptom and often that is what brings pet owners to the vet. Unfortunately, permanent blindness can occur within a matter of hours in cases of rapidly developing glaucoma where the pressure inside the eye becomes very high, very quickly.
Diagnosis and Treatment
Unfortunately, often by the time a diagnosis of glaucoma is made in one eye, the vision is already completely gone in that eye.
Believe it or not, complete loss of vision in one eye is often not obvious because dogs and cats are able to compensate very well using just the other eye. Many pet owners aren’t even aware their dog or cat is entirely blind in one eye.
Treatment in this case will be focused on relieving pain in the blind eye and trying to prevent or halt progression of glaucoma in the other eye.
It’s extremely important to determine why your pet developed glaucoma in the first place, because treatments and prognoses differ depending on what caused the condition.
If your vet suspects glaucoma, unless he or she is an expert in eye diseases and has specialized ophthalmic equipment, the next step will be to visit a veterinary ophthalmologist – and the sooner the better in most cases.
A veterinary ophthalmologist uses specialized tools and equipment to determine what kind of glaucoma is occurring and hopefully, the root cause. In fact, even when a pet’s eyes look normal to the owner, a veterinary ophthalmologist can often find cloudiness in the cornea or other secondary changes that can’t be seen without special equipment.
In the case of secondary glaucoma, it’s really important that the underlying cause be identified and treated whenever possible.
Treatment will depend on the cause and severity of the disease. But the goal is always to alleviate the pressure inside the eye as quickly as possible by reducing the production of aqueous humor and increasing drainage from the affected eye.
There are a number of medications used to treat glaucoma in pets. Some are used topically and some are given orally. But unfortunately, medical treatment of the condition is not nearly as successful with pets as it is with people.
Long term control of primary glaucoma in a blind eye is usually, unfortunately, removal of the eye. As awful as it sounds, it actually provides the very best relief for the dog.
Reducing Your Pet's Risk for Glaucoma
Slowing degenerative changes in your pet’s eyes can reduce the overall risk of glaucoma.
I recommend any dog with glaucoma, or any dog at risk for the disease, be leashed with a harness that fits around the torso rather than around the neck.
- Antioxidants like beta-carotene, vitamins E and C, as well as nutraceuticals such as lutein, astaxanthin and rutin can all be used to reduce the amount of damage that occurs to the cells of the eye.
- Reducing stressors in your pet’s environment is also important to help manage the oxidative damage that occurs throughout the body, including the eyes.
- Eliminating pressure to your dog’s neck is also important, because we don’t want to increase inter-cerebral or intraocular pressure through any type of tight collar or harness system.
- For aging pets and higher risk breeds, I recommend proactively monitoring eye pressure during biannual veterinary wellness exams.
Often, identifying early, subtle pressure changes in the eye that can be addressed medically is the very best way to prevent a fulminant glaucoma crisis.