Ptosis is the involuntary drooping or closure of an upper eyelid. The levator muscle holds the upper eyelid in proper position and moves it up and down. Any condition that affects this muscle will also affect the lid�s position. Most cases of ptosis in an adult come on gradually during the later years of life, as part of the normal aging process. The levator tendon stretches, thins, or loosens its attachment to the eyelid, causing it to sag. This age-related ptosis is called involutional ptosis.
If the condition is acquired, it is usually because of a mechanical factor, such as the lid is too heavy for the muscle to lift or it may be associated with a neurological disease or paralytic disease. Less common causes include injury, previous eye surgery or diabetes.
For more information from other health sites, please visit the following webpages:
Eye Smart, What is Ptosis?
American Association for Pediatric Ophthalmology and Strabismus, Ptosis
The American Society of Ophthalmic Plastic and Reconstructive Surgery, Ptosis (Droopy Upper Eyelids)