Inside the back part of the lid is a tarsal plate which adds rigidity to the lid. The levator muscle is attached to the tarsal plate by a flat tendon called the levator aponeurosis. When the muscle cannot lift the eyelid or lifts it only partially, the person is said to have a ptosis. There are two types of ptosis, acquired and congenital. Acquired ptosis is more common.
Congenital ptosis is present at birth.
Both congenital and acquired ptosis can be, but are not necessarily, hereditary. Acquired ptosis can also be caused by a number of different things, such as disease that impairs the nerves, diabetes, injury, tumors, inflammation, or aneurysms. Congenital ptosis may be caused by a problem with nerve innervation or a weak muscle. Drooping eyelids may also be the result of diseases such as myotonic dystrophy or myasthenia gravis . The primary symptom of ptosis is a drooping eyelid.