Cornea Problems in Cats
The cornea, or clear part of the eye, is covered by a protective layer of surface (epithelial) cells. Most destructive processes affecting the cornea begin with an injury to this layer. Any irritative process, such as a foreign body or cat scratch, can cause a surface injury. Cats with prominent eyes, such as Persians, are especially susceptible. Once the continuity of the epithelium has been destroyed, the injury either heals spontaneously or progresses to a more serious problem. The outcome depends on the magnitude of the injury, how quickly it is recognized, and whether the initiating factor has been identified and removed.
This is defined as an injury to the eye caused by a scratch. Corneal injuries are extremely painful. The cat squints, tears, and paws at the eye, and may be sensitive to light. Often, the third eyelid comes out to protect the injured eye. With an extensive injury, the surface of the cornea surrounding the injury becomes swollen due to edema giving it a cloudy, hazy, or opaque appearance.
The cause of the corneal abrasion can often be suspected from its location. Abrasions in the upper part of the cornea may be caused by misdirected eyelashes on the upper eyelid. Lower corneal abrasions suggest an imbedded foreign body. Abrasions near the inner corner of the eye suggest a foreign body beneath the third eyelid. Even dust blowing onto the cornea may cause a mild abrasion.
Treatment: A cat with a suspected corneal abrasion should be seen by a veterinarian. This can rapidly progress to more serious eye injuries, including corneal ulcer or keratitis. Healing of a corneal abrasion usually takes place in 24 to 48 hours by a process in which the epithelium thins and slides over a small defect. Larger and deeper abrasions require more time. A corneal abrasion will not heal if a foreign body is imbedded in the cornea or beneath one of the eyelids. Accordingly, the cat should be examined for foreign bodies under the eyelids.
Corneal ulcers are dangerous and must receive prompt medical attention. Most are caused by an injury to the cornea. Others are associated with an infection (virus, bacteria, fungus) or a nutritional deficiency. In some cases, the cause is unknown.
Large ulcers may be visible to the naked eye. They appear as dull spots or depressions on the eye surface. Smaller ones are best seen after the eye has been stained with fluorescein. Your veterinarian will gently put a drop of fluorescein liquid or put a tab of paper impregnated with fluorescein onto the eye. The eye is then examined with a blue light in a room with dim lighting. The corneal damage will glow brightly.
Treatment: Early treatment is vital to avoid serious complications or even loss of the eye. Treatment may include atropine drops for pain control (remember, these drops are quite bitter and cats will foam at the mouth if they get any atropine orally) and antibiotics to prevent secondary bacterial infections.
Cortisone, which is incorporated into many eye preparations used for conjunctivitis, should not be put into the eye if you suspect the cat has a corneal injury. This can lead to rupture of the cornea and blindness.
Keratitis is an inflammation of the cornea, or clear window of the eye. This is a painful eye condition and should be distinguished from conjunctivitis. Signs of keratitis include squinting, discharge, rubbing the eye, and protrusion of the third eyelid. Conjunctivitis, on the other hand, is characterized by a chronic eye discharge with little, if any, pain.
There are different types of keratitis. All result in loss of transparency of the cornea, which may lead to partial or complete blindness in the affected eye. Keratitis must be managed by a veterinarian. Initially, topical drops or ointments may need to be given as frequently as hourly or every two hours.
An injury to the surface of the eye can result in the development of an abrasion or ulcer that does not heal and becomes secondarily infected. Trauma is the most common cause of ulcerative keratitis in cats.
An infectious form of ulcerative keratitis is caused by feline herpesvirus. The signs of respiratory infection occur before or at the same time as eye involvement. One or both eyes may be affected.
Treatment: This involves antiviral eye medications, possibly including the new drug cidofovir. Vaccination for the herpesvirus will help but does not totally prevent this disease. Adding lysine to the diet may help, as this amino acid competes with the amino acid arginine, which is essential for herpesvirus replication.
This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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