What is Glaucoma?
Cats experiencing vision loss may not show any immediate symptoms. If the vision deteriorates gradually, it is likely that the cat will be able to continue normal activities. This makes it difficult for owners to notice that anything is wrong until the condition has become severe. If a cat begins to display symptoms of vision loss, a prompt veterinary consultation is recommended. If symptoms develop suddenly, this should be considered an emergency requiring immediate attention.
Glaucoma is a condition that occurs when the aqueous humor fluid in the eye fails to drain adequately, resulting in unusually high intraocular pressure. Feline glaucoma is similar to the human condition. The pressure causes the retina and the optic nerve leading from the eye into the brain to deteriorate. This nerve damage results in vision disorders and can lead to swelling of the eyeball, lens displacement, and destruction of the membranes located within the cornea. Glaucoma is an extremely painful condition and, if left untreated, it will cause partial or total blindness.
Symptoms of Glaucoma in Cats
Depending on the cause of glaucoma, symptoms may progress slowly over time or appear suddenly. The condition may affect one or both eyes. Symptoms may include:
- Cloudy eyes
- Redness of blood vessels in the eye
- Eyeball swelling or bulging
- Rubbing of eyes
- Rapid blinking
- Watery discharge
- Dilated pupils that fail to respond to light
- Vision loss
- Loss of appetite
- Behavior changes
- Headaches (indicated by head pressing)
Primary glaucoma is a rare inherited condition that is more commonly found in Burmese and Siamese cats than in other breeds. It is the result of an anatomical anomaly in an otherwise healthy eye. Primary glaucoma almost always affects both eyes.
Secondary glaucoma is a more common condition and may occur in one or both eyes. Eye disease, injury, or uveitis are the primary causes of secondary glaucoma. Uveitis is a severe inflammation of the eye caused by a blockage of the drainage ducts, usually from scar tissue and other debris. It is commonly found in cats with serious diseases including feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP), feline leukemia (FeLV), or a parasite known as toxoplasmosis. In some cases, secondary glaucoma occurs without a known cause. The condition is more common in older cats.
Causes of Glaucoma in Cats
Primary glaucoma is caused by an improper development of the drainage angle in the eye.
Secondary glaucoma may be caused by several conditions, including:
- Severe eye infections
- Lens dislocation
- Inflammation of eye tissues
- Intraocular bleeding
- Eye tumors
- Injury to the eye
Diagnosis of Glaucoma in Cats
When a cat is brought into the veterinarian’s office with symptoms of vision loss, the first step will be for the vet to review its complete medical history. Owners should provide a detailed description of the symptoms including the onset and severity. Any thoughts regarding other possible causes of the symptoms, previous injuries, or other relevant information should be shared.
A thorough physical examination will be performed, including an eye exam. A tonometer is a diagnostic tool that blows a puff of air into the eyeball to measure intraocular pressure. The presence of high pressure in conjunction with a loss of vision will lead to a diagnosis of glaucoma. A gonioscopy may be used to measure the drainage of fluid from the eye, and in some cases, an electroretinography may be used to determine the permanence of vision loss. X-rays or an ultrasound may be performed to check for other eye abnormalities.
Treatment of Glaucoma in Cats
When a cat presents with glaucoma, the vet should immediately take steps to reduce the pressure in the eye in an attempt to save the cat’s vision. Unfortunately, by the time symptoms arise significant vision impairment has often already occurred. Once vision loss has occurred, it cannot be reversed. When only one eye is affected, treatment may also focus on protecting the healthy eye. Depending on the complexity of the case, a referral to a veterinary ophthalmologist may be necessary.
If the condition is not severe enough to require surgery, it can often be treated with prescription eye drops. Pain medication will be prescribed, as well as dorzolamide and/or timolol for a reduction of intraocular pressure, and steroids for inflammation. When glaucoma is treated with medications only, there is a high likelihood that blindness will eventually occur.
Surgical treatment may involve draining of the fluid to reduce pressure. A procedure known as cyclocryotherapy may be used to alter the fluid-producing cells in the eye. This may stop or slow the progression of glaucoma and works best for early treatment. When blindness has already occurred and there is continued pain and discomfort, it is often recommended that the eyeball be removed. After removal, the empty socket can be sewn shut or an orb may be used to retain the shape of the eye.
In addition to the treatment of glaucoma, any underlying diseases or conditions will also need to be addressed.
Recovery of Glaucoma in Cats
Following a glaucoma diagnosis, frequent veterinary visits will be necessary. Eye pressure must be regularly monitored and the vet will need to watch for drug interactions. Medications may need to be adjusted periodically. If only one eye is affected, preventative measures should be taken to protect the remaining eye.
If the glaucoma was caused by a lens dislocation or uveitis and the condition has been successfully treated, then the prognosis is positive.
If the cat has suffered vision impairment, owners will need to take measures to keep it out of harm’s way. Vision-impaired cats should always be kept indoors in a safe and quiet area. Contact with other animals and small children should be avoided. If possible, keep the cat away from stairs and be aware of sharp corners or other hazards. With a bit of patience, most cats eventually memorize their environment and adapt to life without sight.