A drooping or sagging of the eyelid is medically known as ptosis or blepharoptosis. Drooping eyelids may occur on both sides (bilateral) or on one side only (unilateral), in which case it is more easily noticed. Congenital ptosis is eyelid drooping that is present at birth; when it develops later, it is referred to as acquired ptosis. Depending upon the severity of the condition, drooping eyelids may be barely noticeable or quite prominent. Some sagging of the skin and connective tissues occurs during the normal aging process, potentially leading to drooping of the eyelids. Other causes include conditions that affect the muscles and nerves of the eyelid as well as conditions that affect the skin and connective tissues of the eyelid. Rarely, tumors of the brain or eye area are the cause of drooping eyelids.