Ocular administration of cyclopsorin (CsA) is frequently used as treatment for keratoconjunctivitis sicca (KCS) in canines. Cyclosporin is an immunosuppressive drug that reverses immune-mediated destruction of the lacrimal glands. A study performed by Izci et al. determined that topical administration of a 2% solution of CsA was effective for the treatment of dogs with KCS. In this study, 24 dogs with bilateral KCS were treated with CsA, and lacrimal secretion was measured, using Schirmer tear test (STT) strips. Leukocyte and T-lymphocyte subsets were determined in blood samples. Histopathologic changes as well as CD4+, CD8+, and alpha-naphthyl-acetate esterase-positive (ANAE+) lymphocytes were evaluated. Clinical signs resolved at the end of 1 month in conjunction with significantly increased STT values, compared with baseline values. Two other studies also confirmed these results. Morgan RV et al. and Olivero DK et al also treated canines with formulations of CsA of varying strengths 2% and 1% respectively. Both studies showed improvement in tear production by STT with Morgan showing improvement in 75% of cases and Olivero showing improvement in 81.8% of cases. However, treatment with CsA is often lifelong, because discontinuation of treatment often allows KCS to return. Therefore it is important to counsel patients to be consistent in their treatment in order to prevent potential blindness.