Several medications are used for the treatment of “dry eye” in animals. The most frequently used drug, Cyclosporine A, is a potent, immune-suppressing agent that was ﬁrst used in human medicine to help prevent rejection of transplanted organs. Tacrolimus is also used and was developed to help prevent corneal transplant rejection in people. Tacrolimus is a newer therapy for “dry eye,” and is still used as an experimental drug; the long-term side effects are yet to be determined.
The mechanism of action in the development of “dry eye” is not fully understood at this time; however, an immune-mediated abnormality of the tear producing glands appears to be involved. After institution of treatment, many patients demonstrate an immediate increase in tear secretion, whereas others show improvement without an increase in tears. The drugs used to stimulate tear production, Cyclosporine A and Tacrolimus, work by several different mechanisms: Firstly, they stimulate tear production; normal dogs placed on this drug will experience increased tear production. Secondly, these drugs work through their immunosuppressive capacity; by decreasing the immune-mediated destruction of the tear gland, Cyclosporine and Tacrolimus allow the gland to function in its normal tear-producing capacity. Thirdly, these medications improve the health of the conjunctival cells, which secrete mucus. This is especially important for those patients whose tear gland tissue is so incapacitated that no increase in tear production occurs when these medications are prescribed.
Side effects have been minimal to date; a small percentage of patients have shown some mild eye irritation. If this occurs, refrigeration of the Cyclosporine between uses may decrease the ocular irritation. If your animal still experiences discomfort after trying refrigeration, please contact one of our staff members.
Research for new ocular medications to treat “dry eye” is ongoing, as is the research on the nature of its etiology. With time, multiple medications will be developed to address this disease, and potentially a cure. Currently however, the only form of treatment available is disease control. Your ophthalmologist will prescribe other medications in addition to the Cyclosporine A or Tacrolimus, which is dependent upon the ophthalmic examination ﬁndings and the severity of the patient’s ocular disease.