Corneal abrasion is a cut or scratch on your cornea. The cornea is the clear protective window at the front of your eye. It lies directly over the colored part of your eye (called the iris). Many things can cause a corneal abrasion, such as sand, dust, dirt, wood, or metal shavings that get in your eye. The cornea can also be scratched by a fingernail, a tree branch or a contact lens. Rubbing your eyes very hard is another way that an abrasion can occur.