Prior to the 13th century, little was done to defend the eyes. The skull, cheeks and back of the head was defended early on by
mail and
casque defenses, but it was not until the development of the
heaulm that the face was enclosed. After that, a narrow slit was generally provided to allow vision but to restrict weapons. On bascinet
visors ,the area around the eyes was raised outward to make it very difficult for a weapon, or more importantly, an arrow to find purchase on the iron and penetrate.
