Lacrimostimulants are agents that increase or stimulate natural tear production. Cyclosporine and tacrolimus inhibit T-cell activation and improve natural tear production by a minimizing the T-cell attack on the lacrimal gland and by directly lacrimal stimulation. They are presently the most effective treatments for canine KCS. Cyclosporine is commercially available as a 0.2% ointment (Optimmune) but can be compounded in stronger concentrations as a 1% or 2% drop or ointment. Caution should be taken with the use of 2% cyclosporine as one study showed systemic immunosuppression when used in "small dogs". Tacrolimus is usually compounded as a 0.02% or 0.03% drop or ointment. Either drug can be formulated in an oil or aqueous base. Aqueous-based formulations are easier for owners to apply and may be less irritating than oil-based preparations. Which drug to use depends on personal preference, prior treatment, and severity of the KCS. A stronger formulation is indicated in patients unresponsive to the 0.2% ointment. There is more data on cyclosporine than tacrolimus, but in one study, almost 50% of dogs that were some non-responsive to cyclosporine improved after treatment with tacrolimus. The frequency of application for either drug is typically twice daily, but treatments can be increased to three times daily if response is inadequate. Up to three months of treatment can be required to see the full extent of the response to topical immunomodulators. Normally an improvement in clinical signs is rapid, but three months of treatment is recommended prior to declaring medical failure. Both drugs appear to improve patient comfort and reduce corneal inflammation, scarring, and pigment. In pets that do not respond with improved tear production, continued treatment is still advised to prolong vision and comfort. Some ophthalmologists advocate combination treatment with cyclosporine and tacrolimus in patients that respond inadequately to either drug alone, but such treatment is controversial.

Pilocarpine has historically been used for lacrimostimuation. Two percent pilocarpine at a dosage of 1-2 drops/25 pounds body weight BID in the food is a good starting dose. The dosage is gradually increased until a response is observed or signs of toxicity develop. Toxic signs include salivation, bradycardia, vomiting, or diarrhea. Pilocarpine is mentioned here for completeness, but since cyclosporine was introduced, it has declined in popularity.

Judiciously applied topical corticosteroids are beneficial for many dry eye patients to reduce conjunctival and corneal inflammation and corneal vascular infiltrates. However, pets with KCS are at greater risk for corneal ulceration, and caution is advised, especially in pets with negligible tear production. Neo-poly-bac with hydrocortisone ointment is a good first choice because the steroid is relatively mild but sufficiently strong to be of benefit.

Tear production should be checked two weeks after initiating treatment and periodically thereafter. Cyclosporine or tacrolimus treatments are modified depending on patient response. In dogs with restoration of normal tear production (>15 mm/minute), it may eventually be possible to reduce cyclosporine or tacrolimus to once daily and discontinue other topical treatments. Parotid duct transposition surgery should be considered for dogs that have not responded months of appropriate treatment.

Parotid Duct Transposition

Parotid duct transposition (PDT) surgery should be considered in dry eye patients that are unresponsive to treatments, which remain uncomfortable, or experience recurrent corneal ulcers. Saliva is similar enough in composition to tears to be an acceptable substitute. Possible complications of PDT surgery include mineral precipitates on the cornea and eyelids, chronic epiphora, facial dermatitis, and post-operative stenosis of the parotid duct. Mineral precipitates are the most common complication but can usually be managed with daily cleaning of the eyelids and periodic removal from the corneal surface with a cellulose surgical spear (e.g., 2-3 times annually). Topical 1.38% EDTA solution several times daily may be helpful in reducing deposits. Dietary management can also be helpful, and diet low in mineral content is advised for problem cases.