[Anatomy and physiology of the eyelids]

The eyelids take a prominent part in the protection from the anterior structures of the human visual system and in its maintenance. For moving 14,000 times a day and for producing and eliminating a three layers transparent fluid which is not thicker than eight microns, it's not surprising to find eight different layers in the upper eyelids or five different glands between the lashes and the upper fornix.