Why do people get ptosis?

Ptosis is the drooping of the upper (usually) eyelid. Most people get ptosis because of old age and laxity of the muscle and tendon that lifts the upper eyelid. Other diseases can cause the drooping of the eyelid including myasthenia gravis, stroke muscle degeneration diseases, and abnormal masses behind the eye or injuries. Some babies are born with droopy eyelids and need surgery to improve this. There are a number of surgeries that can be employed to raise a droopy eyelid.

Sometimes the eyelid(s) will droop because the eyeball is irritated or sensitive to light and the lid closes to protect the eye. Here the muscles work fine but the problem of the eyeball needs to be corrected so that the body and eyelid will stop feeling the need to protecting it.