This ancillary study to VITAL will examine the efficacy of omega-3 fatty acids and vitamin D3 in prevention of dry eye disease. The primary aims are to test whether omega-3 fatty acid supplementation (1) reduces the incidence of dry eye disease, and (2) improves the natural history of dry eye disease by relieving symptoms and other impacts on quality of life. Secondary aims are to estimate the incidence of dry eye disease in the US, prospectively examine the natural history of dry disease, explore factors that could modify or influence the impact of omega-3 fatty acid supplementation, evaluate the interrelationship of dry eye disease and depression, and test for possible independent or joint effects of vitamin D3 supplementation in the incidence and natural history of dry eye disease.