Blinking provides moisture to the eye by irrigation using tears and a lubricant the eyes secrete. The eyelid provides suction across the eye from the tear duct to the entire eyeball to keep it from drying out.
Blinking also protects the eye from irritants. Eyelashes are hairs attached to the upper and lower eyelids that create a line of defense against dust and other elements to the eye. The eyelashes catch most of these irritants before they reach the eyeball.
There are multiple muscles that control reflexes of blinking. The main muscles, in the upper eyelid, that control the opening and closing are the orbicularis oculi and levator palpebrae superioris muscle. The orbicularis oculi closes the eye, while the contraction of the levator palpebrae muscle opens the eye. The Müller’s muscle, or the superior tarsal muscle, in the upper eyelid and the inferior palpebral muscle in the lower 3 eyelid are responsible for widening the eyes.
These muscles are not only imperative in blinking, but they are also important in many other functions such as squinting and winking. The inferior palpebral muscle is coordinated with the inferior rectus to pull down the lower lid when one looks down. Also, when the eyes move, there is often a blink; the blink is thought to help the eye shift its target point.
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