Glaucoma in Cats
Dr. Jennifer Welser
Glaucoma is abnormally high pressure in the eye. Inside the normal eye there is constant production and drainage of a watery fluid called aqueous humor. When there is a problem with the drainage of this fluid, the pressure within the eye can increase. High pressure causes damage to the optic nerve, which, in turn, causes vision loss. Causes of glaucoma can be primary (spontaneous) or secondary. Inflammation – Severe inflammation in the eye produces protein and debris that circulate with aqueous humor. This material can clog up the drainage area and block the outflow of fluid. Fluid flow may also be blocked at the pupil if an inflamed iris sticks to the lens, which sits immediately behind it. Chronic inflammation of the iris is the most common cause of glaucoma in the cat.
Primary Glaucoma. Primary glaucoma indicates a problem in the area where fluid leaves the eye. The problem can be structural or one that involves the function of the drainage area of the eye. This form of glaucoma has a tendency to be inherited and is very rare in the cat.
Secondary Glaucoma. Secondary glaucoma develops as a side effect of some other disorder within the eye. Many different eye diseases can interrupt the usual flow of aqueous humor within the eye or disrupt the drainage of this fluid from the eye.
Causes of Glaucoma
The exact precipitating cause of primary glaucoma is unknown. The disease appears to occur spontaneously, often without any warning. Even though the drainage area of the eye may be abnormal since birth, it is not understood why acute glaucoma appears at a particular time, later in life.
Secondary glaucoma is the most important form of glaucoma in the cat and has numerous causes, including the following:
Lens luxation – If the lens becomes dislocated (luxated) and falls into the front chamber of the eye, it can block the flow and drainage of aqueous humor. Lens luxation in the cat is usually a side effect of chronic inflammation of the iris and adjacent tissues.
Tumors – Tumors inside the eye can invade the drainage area and prevent fluid from leaving the eye.
Trauma – If the eye somehow gets injured, it can fill with blood, which may block the drainage pathway.
What to Watch For
Very squinty and painful eye
Dilated pupil that doesn't react to light
Cloudy (whitish/blue) cornea (front surface of the eye)
Enlarged size of the eye (known as buphthalmos)
Vision loss, blindness
Glaucoma generally only affects one eye initially. Depending on the underlying cause of the glaucoma, the other eye may be at risk for developing glaucoma in the future.
Diagnostic tests are needed to recognize glaucoma and exclude other diseases. Tests may include the following:
A complete medical history and general physical examination of your pet. The need for blood work and other general health tests varies.
A complete exam of the eye to confirm the presence of glaucoma and to determine if the glaucoma is primary or secondary. The eye is also assessed for the amount of damage has been done to the optic nerve and retina. Your veterinarian may refer your cat to a veterinary ophthalmologist for a comprehensive examination of the eye, which would include:
Frequent measurements of the pressure inside of the eye (called tonometry)
Gonioscopy to evaluate the drainage pathway with special instrumentation
Ultrasonography of the eye if the eye is too cloudy to be examined in depth. It can help identify lenses that are out of place, tumors, and damage to the optic nerve.
The primary goals of the treatment of glaucoma are to treat or correct any underlying causes, to decrease the pressure within the eye, and to save vision if possible. Treatment of glaucoma in cats may be medical or surgical.
Medical therapy is commonly used when inflammation of the eye is the underlying cause of the glaucoma. Medications are given to decrease the production of fluid inside of the eye, and to control the inflammation. Unfortunately, there are no medications that significantly improve the outflow of fluid from the eye. Glaucoma medications include topical drops and systemic pills. Anti-inflammatory medications are available both as ointments and topical drops.
Medical therapy can also be tried in cases of primary glaucoma.
Surgical therapy is sometimes used for treating primary glaucoma that is unresponsive to medical therapy in the cat. Such surgical therapy involves killing the area within the eye that produces aqueous humor. This may be done with either cryotherapy (freezing) or laser therapy. Another option involves bypassing the drainage area by inserting tubing with a valve into the eye. All of these procedures are performed more frequently in the dog.
Surgical therapy for lens luxation involves opening the eye and removing the dislocated lens manually.
When a tumor is present in the eye and causing glaucoma, surgery to remove the eye (enucleation) is indicated.
When glaucoma does not respond to medications and the pressure within the eye remains elevated, when the animal is persistently painful, or when the eye is blind and medical therapy is too expensive to continue, then surgical removal of the eye may be considered.
Glaucoma is often a very difficult problem to treat. Medications must be administered at consistent times and must often be continued indefinitely. It is important to administer glaucoma medications exactly as your veterinarian prescribes them. Medications should not be stopped just because the appearance of the eye has improved. In the event that vision cannot be saved, understand that such vision loss is not life threatening and the vast majority of cats adjust very well to impaired vision or blindness in one or both eyes.