Keratoconjunctivitis sicca (KCS) is a common eye disease in dogs. The prevalence of KCS in the dog ranges from 1 to 4%. KCS in dogs can cause ocular discharge, pain, corneal scarring and ulceration. In fact, one of the most common causes of a corneal ulcer in the dog is KCS.
Diagnosing a dog with KCS is based on low Schirmer tear testing (<15mm/min) as well as other ocular symptoms blepharospasm, mucoid to mucopurulent discharge, corneal scarring and corneal ulcers.
The best treatment for KCS is a lacrimogenic agent. Cyclosporine is a widely used lacrimogenic agent and is the active ingredient in Optimmune ointment. When treating KCS, cyclosporine is generally used twice daily and it is often compounded as a 1 or 2% drop or ointment. Tacrolimus, another lacrimogenic agent, is often compounded as a 0.02 or 0.03% drop or ointment and is generally used twice daily. Both tacrolimus and cyclosporine are T-helper cell suppressors, however, tacrolimus is more potent than cyclosporine and has some mast cell stabilizing properties. Because of its mast cell stabilizing effects, tacrolimus is often used in people and dogs with ocular allergies.
There is a type of KCS called qualitative tear film deficiency where the Schirmer tear test is greater than 15mm/min but the dog has the ocular symptoms of KCS. With qualitative tear film deficiency, the lipid layer and the mucin layer are abnormal but the aqueous or watery layer is normal. The treatment for qualitative tear film deficiency is either cyclosporine or tacrolimus once to twice daily. A test called a tear break up time can be performed to diagnose qualitative tear film deficiency.
Tear breakup time (TBUT) is a clinical test that is performed by placing a drop of fluorescein stain in the patient’s eye. You carefully observe the tear film under a broad beam of cobalt blue illumination while gently holding the dog with the eyelids spread apart so he can’t blink. The TBUT is recorded as the number of seconds that elapse between the last blink and the appearance of the first dry spot in the tear film. A TBUT under 10 seconds in a dog is considered abnormal.
Some dogs with KCS do not respond to medical treatment because they either do not have lacrimal glands or because their lacrimal glands have atrophied and are no longer capable of producing tears. These dogs may be candidates for either a parotid duct transposition or a labial salivary gland graft. The parotid duct transposition reroutes the parotid duct from the mouth to the ventral conjunctival fornix. This procedure provides saliva to the corneal surface and in most cases improves comfort and corneal health. The labial salivary gland graft is a newer surgery where labial salivary glands are dissected from the mouth and transplanted to either the dorsal or ventral conjunctival fornix. The goals of this surgery are the same as the parotid duct transposition, to provide saliva to lubricate the ocular surface and to decrease the symptoms of KCS. However, neither procedure eliminates the need for topical medical therapy.