Which medication was first used for canine ADDE (KCS) that paved the way for human treatment?

• A. Cyclosporine
• B. Tacrolimus
• C. Latanoprost
• D. Prednisolone

Answer: (A)

Targeting immune-driven damage to the lacrimal gland can restore tear production. In canine keratoconjunctivitis sicca, topical cyclosporine was the first therapy shown to reliably increase tear production by dampening the T-cell–mediated inflammation that damages the lacrimal gland. Cyclosporine binds cyclophilin in T cells and inhibits calcineurin, which blocks IL-2 transcription and T-cell activation. This reduces lymphocytic infiltration of the lacrimal glands, allowing them to resume tear production. This veterinary success demonstrated that modulating the immune response could reverse aqueous tear deficiency and provided the translational path to human dry eye therapy, leading to topical cyclosporine used in humans. While other agents (like tacrolimus, latanoprost, and steroids) have roles in ocular surface disease, cyclosporine was the first to show this pioneering, tear-production–restoring effect in the canine model that spurred human treatment development.