The eyelids play a key role in protecting the eyes. They help spread moisture (tears) over the surface of the eyes when they close (for example, while blinking); thus, they help prevent the eyes from becoming dry. The eyelids also provide a mechanical barrier against injury, closing reflexively when an object comes too close to the eye. The reflex is triggered by the sight of an approaching object, the touch of an object on the surface of the eye, or the eyelashes being exposed to wind or small particles such as dust or sand.
Tears are a salty fluid that continuously bathes the surface of the eye to keep it moist. This fluid also contains antibodies that help protect the eye from infection. Tears are produced by the lacrimal (tear) glands, located near the outer corner of the eye. The fluid flows over the eye and exits through two small openings in the eyelids (lacrimal ducts); these openings lead to the nasolacrimal duct, a channel that empties into the nose.
If the lacrimal glands donâ€™t produce enough tears, the eyes can become painfully dry and can be damaged. A rare cause of inadequate tear production is SjÃ¶grenâ€™s syndrome. The eyes can also become dry when evaporation causes an excessive loss of tears, for example, if the eyelids donâ€™t close properly.
If you need any further information about tears and the eyes in general, please contact Ian Cameron.