A mask for correcting crossed eyes, from 1583. The mask was developed by Georg Bartisch (1535-1606), who was born a peasant near Dresden, Germany. Although he was not rich enough to pursue formal training in medicine, he became a successful barber-surgeon and frequently operated on patients to remove cataracts. He devised this mask to treat crossed eyes (strabismus). The eye slits were positioned in such a way as to force the eye muscles to assume normal lengths and tensions. This illustration was published in Bartisch's "Ophthalmodouleia Das ist Augendienst," 1583 (Treatment of the Eye), a 16th century medical text that was apparently dictated to a scribe, since Bartisch could not write.