Keratoconjunctivitis sicca is an eye disease precipitated by a lack of watery tears, as described in the breakdown of the words: kerato-
(cornea, which is the clear, transparent front of the eye) -conjunctiv-
(conjunctiva, which the delicate membrane lining the eye) -itis
(which means inflammation) sicca
(dryness of the eye)
So, it is an inflammation of the cornea and conjunctiva secondary to dryness of the eye.
As the watery part of the tear film diminishes, the eye tries to compensate by making more mucousy material. In addition, inflammation of the surface of the eye also stimulates the production of more mucous.
Several eye diseases may resemble keratoconjunctivitis sicca. It is important that an accurate diagnosis is made early in the disease because chronic KCS may lead to blindness. Diseases that can appear similar to KCS include: Conjunctivitis. This is a syndrome associated with inflammation of the tissues that line the eyelids and cover the eye. It is sometimes called "pink eye." Clinical signs of conjunctivitis include increased tearing, discharge, redness and sometimes squinting. There are many causes for conjunctivitis. See the Client Education article on Conjunctivitis.
Episclerokeratitis. This is an inflammation of the cornea and sclera (the white outer shell of the eye). This disease is much less common than KCS. The inflammation causes swelling and thickening of the tissues that line the eye. See the Client Education article on Episcleritis for more information.
Dacryocystitis. This is an inflammation and infection of the tear drainage system. There is often a large amount of yellow-green discharge from the affected eye and there may or may not be pain associated with this disease. Discharge often accumulates in the inner corner of the eye and continues even after cleaning. Tear production is normal in this disease; the problem lies in the ducts that drain the tears away from the eye.
Corneal ulceration. An abrasion of the cornea causes discharge and redness of the eye. The onset is usually acute and the eye is painful. A corneal ulcer is diagnosed by applying fluorescein stain to the eye. The eye only takes up stain if ulceration is present. Corneal ulcerations may also occur as a result of KCS, especially shortly after the onset of KCS. It is important that the tear production is measured when a corneal ulcer is present. See the Client Education article on Corneal Ulcers.
Pannus. This is an immune-mediated disease of the cornea that only mildly resembles KCS clinically. A progressive inflammation and pigmentation is present in the cornea that usually starts in the outer corner of the cornea and slowly progresses over the cornea towards the inner corner. This disease is most commonly seen in German shepherd dogs (GSD) and GSD-cross dogs. Tear production is normal in this disease. See the Client Education article on Pannus.
Pigmentary keratitis. Pigment invades the cornea of certain breeds of dogs with very prominent, exposed eyes. This pigment occurs mainly in the area of the cornea closest to the nose, and is common in the pug, shih tzu, Lhasa apso, and Pekingese. Tear production is normal in this condition.