This document discusses corneal physiology through numbers. It summarizes that 90% of incident light is transmitted through the cornea and corneal clarity depends on physical factors like the epithelium, stroma, and endothelium as well as hydration. The stroma makes up 70% of the corneal thickness and contains collagen, GAGs and keratocytes. The endothelium decreases in density with age. Corneal hydration is regulated by stromal swelling pressure, the barrier functions of the epithelium and endothelium, the endothelial pump, evaporation from the surface, and intraocular pressure.