The eyelids serve several valuable functions. Most importantly they provide mechanical protection to the globe. They also provide vital chemical elements to the precorneal tear film, and help distribute these layers evenly over the surface of the eye. During the blink phase the eyelids propel tears to the medial canthus where they enter the puncta of the lacrimal drainage system. The eyelashes along the lid margins sweep air-borne particles from in front of the eye, and the constant voluntary and reflex movements of the eyelids protect the cornea from injury and glare.