For the purposes of this article, I will refer to keratoconjunctivitis sicca as the abbreviate KCS or the common name of dry eye. Calling the disease dry eye is actually quite appropriate, as that is exactly what occurs when dogs and cats are affected by this disease. The cornea (clear coating of the eye) and conjuntiva (mucus membranes of the inner eyelids), are constantly bathed in tear film and kept moistened. This moisture is due to the water component of tear film which accounts for 95% of tears volume,constantly produced by glands that reside in the conjunctiva. Any deficiency of tear production leads to KCS and all subsequent clinical consequences.
Causes for inadequate tear production in dogs and cats, with subequent KCS, include the following:
Distemper Infection In Dogs: KCS can result from a bout with canine distemper virus.
Herpes Virus In Cats: Chronic upper respiratory and/or occular herpes virus in cats can lead to KCS.
Administration of Sulfa Antibiotics: Certain sulfa based antibiotics, most commonly trimethoprim sulfa, are associated with dry eye as a side effect, This, however, is not very common, and KCS commonly subsides once the patient is off the drug
Removal of the third eyelid: When a veterinarian opts to simply remove the third eyelid to treat third eyelid prolapse (a condition commonly called cherry eye), rather than utilize an inversion procedure to replace the prolpased tissue, KCS often results. This is due the third eyelid being rich in tear producing glands and therefore an important souce of tears.
By far, the most common cause for canine KCS is immune mediated destruction of the tear producing glands. The reason this happens is not fully understood, but certain breeds seem to be predisposed, including: Pugs, Cocker Spaniels, Yorkshire Terriers, West Island White Terriers, Miniature Schauzers, and Boxers. While these appear to be the most common breeds affected, however, any breed of dog or cat can be affected. Immune mediated KCS is quite rare in cats.
Diagnosis of KCS begins with visual inspection. In advanced cases, the eye or eyes can be observed with a dry and chronically reddened appearance. However, early to mid staged cases of KCS can look very much like allergic or infectious conjunctivitis. Diagnosis is confirmed by a painless tear strip test that is done right in the examination room called a Schirmir Tear Test. I always recommend also performing a flourescen stain of the cornea to make certain that there are no secondary corneal ulcers.
In the past, KCS was simply treated with artificial tears drops that can be purchased at any supermarket. This was acceptable when there were no other viable options for treatment, but falls short due to the impracticality of the frequency of treatement necessary to effectively help the patient. Now there are much better medical options for effective management of canine and feline KCS.
Cylosporine 2 % solution is the most commonly utilized drop formulation that stimulates tear production to effectively manage KCS, and remains my preferred treatement. In cases where the patient inadequately responds to cyclosporine, then tacrolimus drops are a good second option, with potential for successwhere cyclosporine has fallen short. Tacrolimus is an acceptable first option for treatment as well as cyclosporine, but due to its higher cost and occacional lack of availability, I tend to reserve it only for patients that do not respond to cyclosporine.
In severe cases that do not respond medically, the next option is surgical. A procedure called the parotid duct transposition effectively alleivates KCS, where the outflow from the salivary glands is diverted into the eye.. Normally, the parotid salivary gland empties saliva into the mouth. If this gland is working properly, and has not been affected by the cause of the KCS, this operation can be performed by a specialist eye surgeon. However, there are a number of potential problems with this procedure:
-saliva is not a perfect replacement for tears;
-saliva flow is much less than tear production;
-saliva salt crystals can form in the eye.
For this reason, a Parotid Duct Transposition should not be undertaken lightly, and only after medical treatment has proven unsuccessful or impractical (as with dogs or cats that are too aggressive for the owner to treat..
Prognosis is typically good for canine anf feline patients with KCS. The medical options of cyclosporine drops and tacrolimus are usually all it takes to effectively treat the disease. However, in cases where medical management is not practical or effective, then the paratid duct transposition can be considered as viable
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 11/12/2012