what causes the skin above the eyelid to droop
As you are now probably aware, upper eyelid ptosis is a condition that causes the upper eyelid to appear to be droopy or give a person that sleepy-eye appearance. With this condition, the upper eyelid is lower than it should be (it either covers part of the iris or is very close to covering the iris) and this is caused by a weak eyelid muscle.
In general, if the ptosis is caused by a systemic muscle weakness, other muscles in the face, head, or body may be affected. A drooping eyelid can also be a symptom of a brain tumor or stroke, especially if it comes on within a few days or a few hours or if just one eye is involved.
However, ptosis of the upper eyelid can be a symptom of several health conditions, including diabetes, diseases of the nervous system such as myasthenia gravis, or damage to the third cranial nerve that controls the eyelids. Myasthenia gravis is a serious autoimmune neuromuscular disease that results in nerve weakness.