Understanding Feline Glaucoma
Like their human companions, dogs and cats can lose their vision to glaucoma, but veterinary medicine now offers treatments that preserve an animal's sight. It is important for pet owners to be aware of the symptoms of glaucoma and to act on them quickly because the disease can quickly devastate the eye.
What is Glaucoma?
Glaucoma is essentially abnormally high pressure in the eye. A normal eye constantly produces and drains a watery fluid. If a problem develops with the drainage, pressure inside the eye can build up. High pressure causes damage to the optic nerve, which, in turn, causes vision loss.
What Causes Glaucoma in Cats?
There are primary and secondary causes of glaucoma in cats:
Inflammation inside the eye has many causes. In dogs, they include infectious diseases such as fungal disease, tick-transmitted disease and cataracts. For cats, chronic anterior uveitis, an inflammation of the front of the eye, often leads to glaucoma. One or both eyes can eventually be affected depending on the cause of inflammation.
The fluid outflow pathway in the eye is commonly known as the drainage angle. For proper outflow, the angle needs to be open in a way that the fluid will flow through small holes, as in a sieve. In breeds predisposed to glaucoma, there is usually a narrow angle or inadequate holes in the sieve (known as goniodysgenesis).
What to Watch For
Signs of glaucoma in cats may include:
Glaucoma generally only affects one eye initially. Depending on the cause, the other eye may be at risk for developing glaucoma in the future.
Many diseases can cause a red, squinty, teary and cloudy eye, but glaucoma should always be considered as a cause. Frequently, when the pressure is high, pets are in a lot of pain and hold the eye closed or keep the third eyelid (a pink/red membrane) up over the eye making it difficult to assess.
It is essential to evaluate the pupil in a red, squinty, teary eye with or without the cloudy surface appearance. The pupil is the black “hole” in the center of the eye formed by the iris, which is the colored part of the eye. If the pupil is widely dilated (a large black spot with minimally colored parts visible) and it doesn't constrict (get smaller) in response to a bright light, glaucoma is highly possible. When checking the pupil response, don't be confused by the normal reflection of bluish/green or yellowish/orange that is frequently seen shining through the black hole of the pupil.
Assessing vision can be difficult, but is very helpful. Your pet should blink to a bright light shown into the eye. Without creating airflow or touching any whiskers, see if your pet blinks when you wave your hand in front of the eye (known as a “menace test” because your pet is responding to a menacing gesture). You can also throw objects like cotton balls (anything that won't make a sound when it lands) in front of your pet to see if he follows the object. Setting up mazes can also be helpful; move chairs or garbage cans around in a room that is familiar to your pet, and then see if he can navigate across the room. This type of test will be less effective if only one eye is affected.
Getting Treatment for Glaucoma in Cats
If you suspect that your cat has an increase in pressure in an eye, it is best to treat the problem aggressively because glaucoma can quickly cause severe damage. You can always stop medications if they aren't needed; you can't go back in time and give medications if they were needed.
After taking a complete medical history and doing a physical exam, your vet or veterinary ophthalmologist may diagnose whether your cat in fact suffers from glaucoma through tests that include a complete eye exam; a check of the pressure inside of the eye (called tonometry); gonioscopy, a test that evaluates the drainage pathway; and ultrasound, which can help identify lenses or tumors that are out of place if the inside of the eye cannot be examined by routine techniques.
Treatment for glaucoma is generally aimed at decreasing the production of fluid inside the eye, increasing the flow of fluid out of the eye and controlling any inflammation inside the eye. Topical medications (drops and ointments placed directly on the eye) and systemic medications (pills or injections) are available.
Surgery may also be recommended. This can include trying to “kill” some of the cells that produce fluid inside of the eye by laser or deep-freeze; trying to create a different drainage pathway; removing the eye; placing a prosthesis in the “shell” of the eye; or injecting a medication into the eye to “kill” the fluid producing cells.
What You Can Do for Your Cat
Optimal treatment for your cat requires a combination of home and professional veterinary care. Follow-up can be critical. You should:
If therapy fails, understand that vision loss is not life threatening and the vast majority of animals adjust very well to impaired vision or blindness.