Entropion is when the lower eyelid turns inward toward the eyeball. This can be caused by age, infection, or scarring inside the eyelid. Entropion can cause irritation as your eyelashes rub against the eye.
Left untreated, it can cause infection and lead to loss of vision. Eyelid surgery returns the eyelid with entropion to its normal position.
In these drawings, the eyelid is cut away to show the appearance of a normal eyelid (top) and an eyelid turning inward (bottom).