Eyelid (Human)

In order for the eye to remain healthy, it must be kept moist. This fold of skin automatically sweeps secretions of the lacrimal apparatus and other glands over the sensitive front surface of the eyeball, known as the cornea. The lacrimal gland produces watery secretions in a continuous involuntary process referred to as tearing or lacrimation. The salty fluid flows into a structure known as the lacrimal lake, which is located between the eyeball and the upper eyelid. This lubricating and bathing solution is spread across the surface of the eye at regular intervals by the process of blinking. The rims of eyelids are also lined with about thirty minute oil-producing glands that are located between the eyelashes. Blinking actions function to coat the eyelid with these oils so that they remain flexible and can easily fold. The eyelids are fringed with eyelashes that line the outer rim and are designed to help prevent dust and other foreign particles from landing on the surface of the eye. Eyelids also exhibit protective reflexes such as quickly shutting in response to unexpected oncoming objects and squinting in bright light.