The eyes are lubricated by a film of tears, which keeps the eye moist, protects against infection, and helps eye wounds heal. This film has three layers. The innermost layer is the mucin or mucous layer, which helps spread the middle layer of the tear film across the eye, keeping the front of the eye wet. Tears are produced by a pair of glands known as the lacrimal glands. Each time you blink, new tears are formed in the glands.
Tears travel from the gland through tiny ducts to the surface of the eye.
According to The Schepens Eye Research Institute, about 10 million Americans suffer from dry eye. Symptoms can include a dry, scratchy, or sandy feeling in the eye, as well as stinging, burning, redness, and pain. The condition can have many causes. As people age, the production of tears decreases. The quality of tears may also change, so that tears evaporate from the eye too quickly.