Acquired ptosis is most commonly caused by stretching of the levator muscle in the eyelid, the major muscle responsible for elevating the upper eyelid. Other causes may include interference with the nerve supply to the muscle or occur as a result of aging, trauma, muscular disease, or neurologic disease. As you age, the tendon that attaches the levator muscle to the eyelid stretches and the eyelid may fall, covering part of the eye. Patients may also develop upper eyelid ptosis after cataract surgery, which can sometimes cause the weak tendon to stretch.