A "droopy eyelid" describes an upper eyelid that falls to a lower position than is normal when the eye is open.

It is given the medical name, "ptosis." Drooping of the lid may be present at birth, or it can start in an adult.

For an adult with a droopy lid, the most common cause is stretching of the lid from aging. It can occur in young adults if the lid is manipulated frequently (for example, in those who wear contact lenses).

This change is called "senile ptosis," "aponeurotic ptosis," or simply "age-related ptosis." The stretching occurs in a broad area of tendon-like tissue that helps the levator muscle to lift the lid. Usually, both eyes are affected if this occurs.

Several diseases can also cause ptosis:

• Myasthenia gravis causes muscles to react weakly to nerve signals. This can cause ptosis, as well as weakness of the arms, legs, or breathing muscles.
• A stroke, brain tumor, or brain aneurysm (an abnormally formed blood vessel) can result in a droopy lid. Some brain or nerve injuries cause not only a drooping eyelid, but also double vision or changes in the pupil size.
• Nerve injury from diabetes
• "Horner's syndrome" is a combination of a drooping lid, a small pupil on one side and dry skin on one side of the face, without the ability to sweat. This curious set of symptoms can be the result of a tumor -- often a lung cancer -- that presses against a specific set of nerves at the base of the neck.
• Infection or injury to the lid

Your doctor or an eye doctor can help you decide if you need testing to explain your drooping lid. Plastic surgery can usually correct the problem.