FAS and Keratoconjunctivitis sicca: Abnormal cell apoptosis is presented in the ocular surface tissues of dry eye patients; the proapoptotic factors in the tear and the ocular surface, for instance, Fas (factor-associated suicide)/FasL (fas ligand) and Bax (B-cell lymphoma-2-associated X protein) along with inflammatory factors such as interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-α), and interleukin 6 (IL-6) would increase its expressions and activate apoptotic pathway.