Downward drooping of the upper lid is called ptosis. Ptosis is most commonly caused by stretching out of the muscle that raises the upper lid, called the levator muscle. This is corrected with an operation called a levator advancement that isolates the levator muscle and repositions it relative to other structures of the eyelid. Occasionally, more severe forms of ptosis caused by neurologic or muscular diseases, or present at birth, require a different surgical procedure. In such cases, the forehead muscle is used to raise the lid. In this procedure, called a frontalis sling, the forehead muscle is connected to internal structures of the eyelid by a slender silicone rod carefully placed beneath the surface. With any ptosis procedure, great attention is paid to the health of the surface of the eye prior to surgery.