Keratoconjunctivitis Sicca (KCS) is commonly called dry eye. Certain breeds are more susceptible to KCS because of the anatomy of their eyes. Dogs and cats with short noses and bulging eyes are over represented with dry eye. KCS is a condition or a symptom of reduced tear production. Tears lubricate the cornea, the clear layer that covers the eye, as well as wash away contaminates and carry nutrients and oxygen to the outer surface of the eye. Kerato refers to the cornea. Conjunctiva is the pink fleshy tissue on the under side of the eyelids. “Itis” means inflammation. And, sicca means dry. So, KCS simply means dry, inflamed eyes. Symptoms of KCS include a stringy mucous discharge, pain and rubbing at the eyes, and the hair around the eyes being matted. Untreated dry eye can lead to corneal ulceration and scarring, reduced vision, and even eye loss.
Tear film is composed of three layers: a mucous portion, an aqueous (watery) portion and a lipid (fat) portion. In KCS, the inability to clear mucous from the eye due to the absence of the aqueous tear portion of the film and increased mucous production in response to irritation give the characteristic dry appearance to the cornea. The aqueous portion carries essential components necessary for corneal health including oxygen, moisture, and nutrients and rinses the surface free of debris. Without the aqueous portion of tear film, irritants and bacteria collect in the mucoid discharge and the cornea is deprived of oxygen leading to damage and infection. Without normal lubrication, the formation of blood vessels and pigmentation on the cornea develop leading to vision loss with chronic KCS. Ulceration can occur, and infection can become established. In severe cases, the eye can rupture and atrophy (shrink). Complete eye loss is possible.
KCS is easily diagnosed. A calibrated absorbent strip of paper called a Schirmer Tear Test Strip is held against the eyeball for sixty seconds. Tears will wet the strip and the moisture line will climb along millimeter graduation marks on the paper. Normal tear production will measure fifteen millimeters or more in one minute. Any lower measurement is considered abnormal. Eleven to fourteen millimeters is borderline for KCS. Six to ten millimeters is diagnostic. And five or less is severe dry eye. Other ophthalmic tests may be performed during an eye exam to detect corneal ulceration (fluorescein stain uptake test) and glaucoma (tonometry).
Causes of KCS can include feline Herpes virus, canine distemper, Sulfa-based antibiotic use, trauma to the lacrimal glands, and cherry-eye surgery. The most common cause of KCS however, is an immune-mediated condition that causes destruction of the tear-producing glands. The treatment of choice for this condition is the use of cyclosporine in a topical ophthalmic medication (Optimmune). Cyclosporine is an immunosuppressive drug that stimulates tear production thereby reversing the effects of KCS. It is applied topically to the eye once or twice daily on an ongoing basis. Adjunct treatments may include artificial tears, antibiotics, and pilocarpine – a cholinergic drug that may increase tear production.
80% of animals with KCS will respond to some degree to cyclosporine treatment. It is most effective for immune-mediated disease. The severity of the reduced tear production and amount of eye damage that has already occurred will determine the amount of improvement to be expected.
