Entropion is the inward rolling of the edges of the eyelid which causes the horse's eyelashes to come into contact with the surface of the cornea. It is either anatomical from too much eyelid skin, associated with malnutrition, dehydration, atrophy of orbital fat due to a systemic disease, or occurs secondary to enophthalmos from eye pain. In adult horses, entropion is usually associated with muscle spasms from chronic eye pain or previous eyelid trauma.