But besides serving as barriers, the lids and lashes also help our eyes stay moist. Without moisture, our corneas, which serve as protective domes for the front of the eyes, would dry out and could become cloudy or injured. Working with our lids and lashes, the protective system of glands and ducts called the lacrimal system keeps our eyes from drying out. Small glands at the edge of the eyelid produce an oily film that mixes with the liquid part of our tears and keeps them from evaporating. These glands are located under the brow bone behind the upper eyelid, at the edge of the eye socket, and in the lids.
Eyelids move tears across the eyes.
Tears keep the eyes lubricated and clean and contain antibodies that protect the eyes from infection. They drain out of the eyes through two ducts called punctum or lacrimal ducts , one on each of the upper and lower lids. From these ducts, tears enter small tubes called canaliculi , which are located at the inner corner of the eyelids. From the lacrimal sacs, tears move down through the nasolacrimal duct and drain into the back of the nose. When you blink, the motion forces the lacrimal sacs to compress, squeezing tears out of them, away from the eyes, and into the nasolacrimal duct.