TRPA1 and Keratoconjunctivitis sicca: Besides the thermal sensation, they have many functions such as protection from dry eye (humidity detectors sensing the evaporation of the corneal surface or inhibition from hypotonic challenge of the epithelium; TRPV4, TRPM8) and injury (TRPV1, TRPA1), wound healing (epithelial cell proliferation; TRPV1, TRPV3, and TRPC4), and contribution of pain and inflammation (TRPV1).