Eyelid

Definition: An eyelid is a thin layer of skin that covers and protects the eye. The eye contains a muscle that retracts the eyelid to "open" the eye either voluntarily or involuntarily. Human eyelids contain a row of eyelashes that protect the eye from dust particles, foreign bodies and perspiration. The main functions of the eyelid are to regularly spread tears on the surface of the eye to keep it moist and to protect the eyes from foreign bodies.