Ptosis (droopy eyelids) refers to a situation in which the eyelids are not as open as they should be. This situation is caused by a weakness of a muscle that opens the upper eyelid. When ptosis is mild, it is just a cosmetic problem. However, ptosis can interfere with vision if it is severe enough to block the vision in the eye. In infancy, it is important that ptosis be eliminated so that vision will develop normally. Correction of ptosis usually requires surgery on the eyelid(s).