What is keratoconjunctivitis sicca?
Keratoconjunctivitis sicca (KCS) is commonly referred to as “dry eye”. The term means drying and inflammation of the cornea and surrounding tissues.
What causes “dry eye”?
Tears are required to lubricate the cornea and remove any debris or infectious agents that may contact the eye. The tear film is a mixture of mucous, fatty liquid and water. Any condition that impairs the ability to produce adequate amounts of tear film can result in “dry eye”. Some of the common causes of KCS
- Immune-mediated diseases that damage the tear producing glands. This is the most common cause of KCS and is poorly understood. The body’s immune system attacks the cells that produce a portion of the tear film resulting in decreased production. This is thought to be an inherited disorder.
- Systemic diseases such as canine distemper virus Medications such as certain sulphonamides (sulfa drugs)
Certain breeds are more likely to develop KCS. These breeds include the West Highland White Terrier, Cocker Spaniel, Lhasa Apso and Yorkshire Terrier. A congenital form of KCS is recognized in Cavalier King Charles Spaniels. This breed is observed to have poor development of the tear producing glands in affected dogs.
What are the clinical signs of “dry eye”? Most dogs have painful, red and irritated eyes. They often squint, blink excessively or hold the eye shut. Corneal ulceration is often present. There is often a thick, mucoid discharge present. This is the result of the decrease in the aqueous (watery) component of the tear film. In chronic cases, there is often a history of recurrent eye injuries, ulcers or conjunctivitis. Many dogs will develop corneal scarring that can be seen on close observation. Corneal scarring often looks like a dark film covering the eyes. You can often see tiny blood vessels coursing throughout the cornea called neovascularization. A dog can not see through corneal scarring and vision may be reduced in many cases. The eyes often have a dull, lusterless appearance due to the corneal drying. KCS most commonly affects middle aged to older dogs. Both eyes are usually affected although one eye may appear worse than the other.