TNF and Keratoconjunctivitis sicca: Pathophysiological theories suggested and basic science research proved that, in aqueous deficiency states such as Sjögren's syndrome, reduced hydration of the ocular surface may initiate or contribute to the development of dry eye by increasing apoptosis and further induction of proinflammatory cytokines including IL-1, IL-6, IL-8, and TNF-α [30].