Ptosis refers to drooping eyelids. In general, ptosis is divided into several types, determined by the cause of the drooping eyelid.
Myogenic ptosis is usually a reflection of a systemic muscle disorder.
When the muscles are weakened by disease, they cannot pull the eyelid up into position. The muscles that raise the eyelid are the levator muscle and Muller's muscle. This is a disease in which the voluntary muscles in the body weaken due to abnormalities within the muscles, themselves. People with myasthenia gravis will often have drooping eyelids as well as crossed eyes due to imbalance of the muscles that control eye movement. In congenital myogenic ptosis, the eyelid muscles are either scarred or do not work.