☆ The role of natural tears 98.2% of the composition of tears is water and 1.8% is solid, which is weakly alkaline. In addition to proteins and inorganic salts, the solid also contains cell growth factors, such as lactoferrin, lysozyme, lactoperoxidase, epidermal growth factor, endothelin-1, and alkaline fibroblast growth factor. Protein can reduce the surface tension of tears, and salt can maintain a certain osmotic pressure, so that tears can be evenly distributed on the surface of the eye, forming a transparent and smooth protective film. Dong Nuo, Ocular Surface and Corneal Diseases, Xiamen Eye Center, Xiamen University