High Quality Content by WIKIPEDIA articles! Entropion is a medical condition in which the eyelid (usually the lower lid) folds inward. It is very uncomfortable, as the eyelashes constantly rub against the cornea. Entropion is usually caused by genetic factors and may be congenital. Entropion can also occur secondary to pain of the eye (leading to self trauma, scarring of the eyelid, or nerve damage.) The upper or lower eyelid can be involved, and one or both eyes may be affected. When entropion occurs in both eyes, this is known as "bilateral entropion." Trachoma infection may cause scarring of the inner eyelid, which may cause entropion. In human cases, this condition is most common to people over 60 years of age.