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.
Below is an overview of feline glaucoma followed by in-depth information about the diagnosis and treatment options for this disease.
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 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:
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.
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.
Diagnosis of Glaucoma in Cats
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.
Treatment of Glaucoma in Cats
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.
In-depth information About Glaucoma in Cats
Glaucoma is an elevation of the pressure within the eye that is incompatible with normal function of the eye. It is a disorder of the outflow of fluid (aqueous humor) from the eye and not a disease of overproduction of fluid within the eye. Sudden, high elevations of pressure within the eye can cause devastating and irreparable damage to the retina (which acts like the film a the camera) and the optic nerve (which sends information from the eye to the brain).
The causes of glaucoma are both primary (spontaneous, probably inherited) and secondary (arise in association with other diseases within the eye).
Primary Glaucoma in Cats
The fluid outflow pathway in the eye is commonly known as the drainage angle. For proper outflow, the angle needs to be open and functioning properly. The drainage area looks and acts almost like the sieve in a kitchen drain. Rarely in cats, this drainage angle can be abnormal. Either the access to the sieve is narrow or the drain behind the sieve does not work properly. Even though the fluid passes through the sieve it does not drain into the veins around the eye well and backs up, causing the pressure in the eye to increase.
Secondary Glaucoma in Cats
Inflammation inside of the eye that gives rise to glaucoma has many different causes. In the cat, chronic anterior uveitis (an inflammation of the iris and surrounding tissues) is caused by feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), feline infectious peritonitis virus (FIP), and toxoplasmosis. In some cases of chronic inflammation, the cause is never determined. One or both eyes may be affected by the inflammation, and one or both eyes may develop glaucoma.
Tumors within the eye generally occur in older pets. Only one eye is usually affected and the progression to glaucoma may be relatively slow.
Trauma can happen to any outdoor cat, at any age (hit by car, hit in the head, falling, attacked by another animal).
Lens luxations (dislocations) usually only occur in the cat in association with chronic anterior uveitis. The chronic inflammation causes the small fibers that hold the lens in position to break down. When enough fibers are broken, the lens can become dislocated. Glaucoma is most likely when the lens falls into the front chamber of the eye and becomes trapped in front of the pupil.
What to Watch For
Many diseases can cause a red, squinty, teary and cloudy eye, but glaucoma should always be considered as a cause of these signs. Frequently, when the pressure is high, the cat is quite painful and holds the eye closed or keeps the third eyelid (a pink/red membrane) up over the eye.
If the pressure inside the eye remains elevated for some time, the eyeball may actually stretch and enlarge. As the eye enlarges or becomes buphthalmic, the eyelids may no longer be able to protect the surface of the eye, and the eye may be traumatized easier.
Assessing vision in the cat can be difficult. Your pet should blink and try to close the eye when a very bright light is shown into the eye. Without creating airflow or touching any whiskers, see if your cat 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 try to 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. Remember that a cat with good vision in one eye will act normally, so it may not be possible to tell if vision is altered in the glaucomatous eye.
In-depth information About Diagnosis of Glaucoma in Cats
Veterinary care includes both diagnostic tests and subsequent treatment recommendations.
A complete medical history and physical examination is often obtained by your veterinarian. Certain medical tests are needed to search for an underlying disease when the glaucoma is discovered to be secondary.
A complete ophthalmic examination is indicated to confirm the presence of glaucoma and to help determine if other eye diseases have led to the glaucoma. A comprehensive examination involves measurement of eye pressure (tonometry), staining of the cornea with fluorescein to detect ulcers, close scrutiny of the front of the eye for signs of inflammation or dislocation of the lens, and examination of the back of the eye to detect retinal damage. Your veterinarian may refer your cat to a veterinary ophthalmologist because a variety of specialized instruments may be needed to complete the evaluation, including a tonometer, a slit lamp biomicroscope, and an instrument to examine the retina.
The eye examination may answer some of the following important questions. Answering these questions helps to determine the cause of the glaucoma and the prognosis:
What is the actual pressure within the eye?
Is the pupil dilated (completely open)?
Where is the lens?
How much inflammation is inside of the eye?
Are there any indications of a tumor or of trauma?
Do the retina and optic nerve appear healthy?
Is the cornea too cloudy to examine the interior of the eye?
Is there any evidence within the eye that a systemic disease may be present in the cat?
Other tests may include:
Gonioscopy involves using a special lens placed on your pet’s eye so that the drainage angle can be viewed. Gonioscopy can also be used to determine if a tumor is invading the drainage area. Depending on the temperament of your pet, this test is generally done with just topical anesthetic drops.
If the glaucoma is secondary to inflammation within the eye, then a complete laboratory work-up is often undertaken to determine a cause. Tests for FeLV, FIV, FIP and toxoplasmosis are submitted, as well as a complete blood count and biochemistry profile.
If a tumor is found within the eye, then a complete blood count, biochemistry profile and X-rays of the chest are performed to try and determine if the tumor has spread to other areas of the body.
In-depth information About Treatment of Glaucoma in Cats
Treatment for glaucoma can be broken down into medical and surgical care. Depending on the cause of the glaucoma, different options are available.
Acute glaucoma is uncommon in the cat. Glaucoma is much more likely to develop slowly in the cat. However, if acute glaucoma is encountered, then several medications are available to attempt rapid decrease of the pressure within the eye. These include injectable, oral and topical medications.
Topical products that are commonly used in cats to decrease the production of fluid in the eye include beta-blocking agents (especially timolol or levobunolol) and carbonic anhydrase inhibitors (especially dorzolamide). These two classes of drugs can also be used together (Trusopt = timolol and dorzolamide).
Other topical products that are used less often in cats include phospholine iodide, pilocarpine, and latanoprost. These products are irritating and may worsen inflammation within the eye.
Oral and topical anti-inflammatory drugs are used to treat any underlying uveitis in the eye: prednisone, triamcinolone, and dexamethasone (oral drugs) may be used when all infectious causes of uveitis have been ruled out. Topical steroids include prednisolone acetate, prednisolone phosphate, and dexamethasone. Oral nonsteroidal anti-inflammatory drugs, such as baby aspirin may be used if oral steroids cannot be given. Never give acetaminophen (Tylenol) to cats, as it is very toxic to them The topical nonsteroidal anti-inflammatory drugs are also avoided when glaucoma is present because they may aggravate the elevated pressure within the eye.
Laser or cryocycloablation – These procedures use a laser or freezing probe to kill the area in the eye that produces aqueous humor. These techniques are used mainly to treat primary glaucoma, which is very rare in the cat.
Gonioimplant or goniovalve insertion – This surgery involves placing a small tube in the eye to by-pass the abnormal drain in the eye, and to allow fluid to drain into the tissues around the eye. It is also used for treating primary glaucoma.
Enucleation – Enucleation is removal of the eye with permanent closure of the eyelids. This surgery is undertaken if the eye is blind or if a tumor is present inside of the eye.
Surgical therapy for lens luxation involves opening the eye and removing the dislocated lens manually, particularly if there is potential for vision and the eye is not terribly inflamed or infected.
Home Care for Cats with Glaucoma
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical and may involve the following:
Administer prescribed medication(s) as directed and be certain to alert your veterinarian if you are experiencing problems treating your pet. Repeated trips to your veterinarian are important in order to monitor the pressure within the eye and to make adjustments in medications.
Understand the medications that your pet is on and what each one is used for. Ask your veterinarian about potential side effects to the drugs and how to monitor for those side effects. Also ask your veterinarian about alternate plans should side effects be experienced by your cat.
Be aware that both the underlying chronic uveitis, as well as the glaucoma, are diseases that may require long-term therapy and monitoring.