A corneal abrasion usually results from a foreign body, such as a cinder or a piece of dust, dirt, or grit, which becomes embedded under the eyelid. Even if the foreign body is washed out by tears, it may still injure the cornea.

A small piece of metal that gets in the eyes of workers who don’t wear protective glasses quickly forms an abrasion and then forms a rust ring on the cornea. Abrasions also commonly occur in the eyes of people who fall asleep wearing hard contact lenses. A corneal scratch produced by a fingernail, a piece of paper, or another organic substance may cause a persistent lesion. The epithelium doesn’t always heal properly, and a recurrent corneal erosion may develop, with delayed effects more severe than those of the original injury.