TF and age: It is also a messenger of oxygen free radicals and has cytotoxicity, which indicates extensive lipid oxidative damage.[48] Besides, DED mice induced by sleep deprivation had tears of a high level of H2O2, along with low expressions of GSH and GPXs.[49] SOD1‐knockout mice showed a deterioration of the TF function, which was considered to mimic age‐related DED.[50, 51] When excessive ROS were removed, the quality and quantity of tears and the stability of the TF were all obviously improved.[51]