The eyelids play a key role in protecting the eyes. 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. If the lacrimal glands don't produce enough tears, the eyes can become painfully dry and can be damaged. The eyes can also become dry when evaporation causes an excessive loss of tears, for example, if the eyelids don't close properly. Blockage can be partial or complete. This type of blockage usually disappears without treatment by the age of 6 months, as the nasolacrimal system develops.