KCS (keratoconjunctivitis sicca) is a disease of the tear secreting glands that results in reduction or lack of tear production. The superficial layers of the eye, including the cornea and conjunctiva, as well as the eyelids depend on tears for nutrition and protection. Without tears, these structures are highly susceptible to disease and trauma.
Some breeds of dogs, such as the American Cocker Spaniel, Miniature Schnauzer, Poodle, Shih Tzu, Lhasa Apso, Pug, and English Bulldog are predisposed to this disease due to genetic factors. We also see this clinical disease in felines (i.e. Persians) and exotic species.
The precorneal tear film is composed of three layers:
1) an outer oily layer, produced by the meibomian glands.
2) the large aqueous layer, secreted by the lacrimal and accessory lacrimal gland. 3) the basal mucus layer, produced by the conjunctival goblet cells.
Important antibacterial enzymes are present within tears. The aqueous portion of the tears is measured by the Schirmer Tear Test. Normal values should range from 15 to 25mm./60 secs. Clinical disease is observed when the precorneal tear film falls below these values. Low Schirmer tear test values, along with commonly observed clinical signs help point the
ophthalmologist to a diagnosis. Some of these clinical signs include a thick mucopurulent discharge which accumulates on the eyelid margins and surface of the eye, red eyes, repetitive corneal ulcers, and excessive facial rubbing. As the disease progresses, blood vessels and pigment invade the cornea, in which varying degrees of visual impairment may occur if not treated aggressively.