Dry eye disease is a common and often underdiagnosed condition that affects > 10% of the adult population, > 65 years of age in the US. This condition has been classified into two separate, but overlapping, categories--aqueous deficiency and evaporative loss. Diagnosis is confused by the lack of a single diagnostic test. Fluorescein break-up time is one of the best screening tests and is augmented by Lissamine green supravital staining. New concepts of pathogenesis have shown that dry eye disease appears to be caused by inflammation mediated by T-cell lymphocytes. This finding led to the study and FDA-approval of topical 0.05% cyclosporin A (Restasis) for the treatment of dry eye disease. 0.05% Cyclosporin A offers the first therapeutic treatment for patients with moderate-to-severe dry eye disease due to aqueous deficiency.