Dry Eye (Keratoconjunctivitis Sicca) in Cats
Keratoconjunctivitis sicca is a disorder of the tear glands that results in insufficient aqueous tear production and a correspondingly dry cornea. The tear film contains less of the aqueous layer and more of the mucus layer. In consequence, the classic sign of dry eye is a thick, stringy, mucoid to mucopurulent discharge. Since this type of discharge can also be seen in cats with conjunctivitis, cats with dry eye may be mistakenly treated for chronic conjunctivitis for long periods with little or no improvement.
Herpesvirus is considered to be a primary cause of dry eye in cats. Luckily, this disease syndrome is less common in cats than it is in dogs. A congenital form of this disease occurs in Burmese cats.
In a cat with dry eye, the bright, glistening sheen normally seen in the eye is replaced by a lackluster appearance in which the cornea is dry, dull, and opaque. Recurrent bouts of conjunctivitis are typical. Eventually, the cornea becomes ulcerated or develops keratitis. Blindness may ensue.
- Dry eye can have several causes. Some specific conditions that predispose a cat to dry eye include the following:
- Injury to the nerves that innervate the lacrimal glands. A branch of the facial nerve that activates the tear glands passes through the middle ear. Infections in the middle ear can damage this branch, affecting the tear glands as well as the muscles on that side of the face. In this case, the opposite eye is not affected.
- Injury to the tear glands themselves. Partial or complete destruction of the tear glands can follow systemic diseases. For example, feline herpes may block the glands. Bacterial blepharitis or conjunctivitis can destroy the tear glands or block the small ducts that carry the tears into the eye. A number of sulfonamide drugs are toxic to tear glands. Tear gland injuries may be partially reversible if the underlying cause is eliminated.
The diagnosis of dry eye is made by measuring the volume of tears. The Schirmer tear test involves placing a commercial filter paper strip into the tear pool at the inner corner of the cat' s eye and leaving it for one minute to see how much of the strip is wetted. Normally, the strip should be wet to a length of 12 to 22 mm.
Treatment: For many years, the frequent application of artificial tears was the only treatment available for dry eye. But use of ophthalmic cyclosporin has revolutionized treatment and greatly improved results. Cyclosporin reverses, or at least halts, the immune-mediated destruction of the lacrimal glands.
Cyclosporin ointment is applied to the surface of the affected eye. The frequency of application must be determined by your veterinarian. The result is not immediate. Artificial tears and topical antibiotics should be continued until the Schirmer tear test indicates that the volume of tears is adequate. Treatment is life-long.
When damage to the lacrimal glands leaves little or no functioning tissue, cyclosporin is not likely to be effective. This is also true if your cat's problem does not have an immune basis. Artificial tears (drops and ointments) prescribed by your veterinarian must then be instilled into the cat's eyes several times a day for life. Ointments are less expensive and do not need to be applied as frequently as drops. Saline drops should not be used because they aggravate the problem by washing away the lipid layer of the tear film.
Surgical treatment can be considered as a last resort, when medical management fails. The operation involves transplanting the duct of the parotid salivary gland up into the corner of the eye. The saliva takes the place of the tears. The operation has several significant disadvantages. One is that the volume of tears may be more than the drainage system can handle. This can result in a watery eye and the accumulation of mineral deposits on the cornea and face.
This article is excerpted from “ Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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