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
(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.
There are other eye diseases that may resemble keratoconjunctivitis sicca. It is important that an accurate diagnosis is made early in the disease because the treatments vary depending upon the eye disease present.
Diseases that can appear similar to KCS include: Conjunctivitis. Conjunctivitis is inflammation of the tissues that line the eyelids and cover the 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.) With most forms of conjunctivitis, the tear production is normal or high.
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 Ulceration.
Other forms of keratitis. In the cat, there are several forms of corneal inflammation that may appear somewhat similar to the corneal changes associated with KCS. It is believed that these disorders may also be caused by feline herpesvirus. They include eosinophilic keratitis, stromal keratitis and corneal sequestration. See the Client Education article on Corneal Sequestration.