Ptosis refers to a drooping eyelid that creates a hooded effect over the eyeball. It can affect one or both eyelids. In rare cases, children are born with this condition (congenital ptosis) or develop it at an early age. However, most people affected by ptosis develop it in adulthood when eyelid muscles weaken and excess tissue around the eyelid pushes the lid downward. Other less frequent but not uncommon causes of ptosis include injury, eye disease and tumors. It can also occur as a side effect of eye surgery. In most cases, surgery is necessary to correct ptosis. However, depending on the cause, medicated eye drops may also improve how wide the eyelids open.