You may not be aware of it, but, every time you blink, natural tears are spread across the front surface of your eyes. Healthy eyes are continuously covered by this tear film that is designed to stay stable between blinks.
The tear film consists of 3 layers:
- The outer, or lipid, layer is very thin and oily. This layer, which floats on the surface of the tear film, is secreted by glands located just behind the lashes in the lids. The outer layer prevents the tear film from evaporating.
- The middle, or aqueous, layer is secreted by glands located behind the eye. This is the thickest layer and provides the eye surface with oxygen and various nutrients.
- The inner, or mucin, layer is secreted by goblet cells normally present on the surface of the eye. This layer coats the eye's surface (epithelium) with a substance called mucin, which enables tears to "stick" to the surface of the eye.