Ptosis means to droop. In ophthalmology it refers to the drooping of the upper eyelid. The lid may drop only slightly or it may drop enough to partially or completely cover the pupil, restricting or obscuring vision.
It can affect one or both eyelids, and often does so asymmetrically.
Some people are born with ptosis, however the more common form of ptosis develops as we get older and is caused by the separation or stretching of the levator muscle tendon.
The levator muscle is responsible for lifting the eyelid.
This can occur as a result of ageing and is slightly more common in contact lens wearers, people who have had eye surgery such as cataract extraction or people who have had severe inflammation of the eyelids or conjunctivitis.
Some forms of ptosis are inherited. Occasionally ptosis is associated with other more serious neurologic conditions.