Is it?about 2 years ago

TEARS

Each tear has three layers: 1. An inner mucus layer that keeps the whole tear fastened to the eye. 2. A watery middle layer (the thickest layer) to keep the eye hydrated, repel bacteria and protect the cornea. 3. An outer oily layer to keep the surface of the tear smooth for the eye to see through, and to prevent the other layers from evaporating.