Glaucoma in Cats: Causes, Diagnosis & Treatment
Feline glaucoma is an eye disease characterized by high eye pressure (aka intraocular pressure). It can cause pain and potentially blindness. The increase in eye pressure is caused by reduced drainage of the aqueous humor — a clear fluid that circulates between the cornea and pupil.
Normal eye pressure in cats generally ranges from 10 to 20 millimeters. Pressure may vary based on the time of day, the cat's level of excitement or anxiety and their positioning. Eye pressure above 25 mm or a significant difference in pressure between eyes — generally greater than 7 to 8 mm — is considered abnormal.
Thankfully, Glaucoma in cats is relatively uncommon compared to glaucoma in dogs. However, the actual prevalence of the disease might be higher since many cases may go undiagnosed due to the often subtle nature of the associated clinical signs.
Causes of Glaucoma in Cats
Causes of feline glaucoma can be divided into two major categories:
- Primary Glaucoma: Primary failure of the eye's ability to drain fluid
- Secondary Glaucoma: An underlying disease that obstructs the normal outflow of fluid in the eye
Primary glaucoma is hereditary or breed-related and is quite rare in cats. Certain breeds, such as the Burmese, Persian and Siamese are more prone to primary glaucoma than other breeds. The onset of signs typically occurs in one eye first. However, if one eye develops glaucoma, There's a high likelihood that the other eye will eventually become affected as well.
Among cats with glaucoma, secondary glaucoma is more common. It occurs secondary to another disease. Getting diagnostic testing to determine the underlying cause of the glaucoma is critical. Once the cause is determined, your veterinarian can recommend appropriate treatment and give a prognosis for your cat's vision loss.
Common Diseases That Cause Feline Glaucoma
The most common underlying diseases that result in feline glaucoma include:
- Neoplasia: Neoplasia refers to an abnormal growth of tissue. Intraocular neoplasia, often a cancerous mass, is the leading cause of glaucoma in cats, with melanoma and lymphoma being the most common types of cancer affecting the eye.
- Anterior uveitis: Refers to inflammation in the front portion of the eye and is a major cause of feline glaucoma.
- Intraocular hemorrhage (Bleeding inside the eye): This most commonly occurs secondary to high blood pressure or trauma.
Signs of Glaucoma in Cats
Clinical signs of feline glaucoma are often very subtle and may be difficult for cat parents to notice. Signs of feline glaucoma include:
- Eye discharge
- Dilation of the pupil
- Prominent blood vessels on the white of the eye
- A hazy or blue appearance to the eye
- Loss of vision
In later stages of the disease, the eyeball becomes enlarged and looks bulgy, and blindness sets in. Cats respond to the discomfort differently. In most cases, though, cats don't show obvious signs of severe pain despite this being a very painful condition. Unfortunately, this means that many cats are diagnosed in the late stages of the disease and are already blind at the time of diagnosis.
Diagnosis and Treatment of Glaucoma in Cats
If you suspect your cat has glaucoma, this should be considered an emergency. Your cat should be evaluated by a vet as soon as possible to reduce the risk of further damage to the eye. Vets diagnose glaucoma in cats based upon clinical signs and by measuring eye pressure. Your vet may use multiple devices to do this.
Unfortunately, in most cases of feline glaucoma once vision is lost it can't be restored. In cats with primary glaucoma, vision loss occurs gradually over time, even with treatment. In cats who have secondary glaucoma, the prognosis depends on the underlying disease causing the glaucoma as well as how the underlying disease and the glaucoma respond to treatment.
There are medicines that can help lower eye pressure and treat glaucoma in cats. Topical medicines must be applied consistently, multiple times a day. While it can be challenging to give your cat medicine, it's not impossible and your vet can help you come up with tricks to make your life easier.
Sometimes the recommended treatment for feline glaucoma is surgery to remove the eye. In cats with irreversible blindness or where cancer is the suspected underlying cause of the glaucoma, removing the eye is usually the most appropriate treatment option. Although it can be stressful to make the decision to remove your pet's eye, remember that the eye is extremely painful. Cats actually do very well with this surgery because a source of discomfort has been removed, and they are usually already adapted to vision loss in the affected eye. Even cats that are blind in both eyes can adapt and do very well following surgery.
Jessica Seid is an emergency veterinarian practicing in the New England area. She is graduate of North Carolina State College of Veterinary Medicine and has been in the field for 10 plus years. When not at work helping her pet patients, she enjoys spending time with her husband, daughter and their French Bulldog.