Emergence of concave spectacles for myopia

Background. Convex spectacles for presbyopia had been in use since the late 13th century, primarily in Italy. By the mid-15th century, the need for correcting myopia (nearsightedness) drove the development of concave lenses. Florence emerged as a leading center for optical research and spectacle manufacturing, benefiting from advances in perspective and geometry that informed lens grinding techniques.

The Cusa Attribution. Some accounts attribute concave lenses to Nicholas of Cusa. The cited reference entry presents De beryllo as a 1450 treatise, but its quoted description concerns concave and convex beryl used as a magnifying glass rather than spectacles. It says only that Cusa may have known of Florentine lens developments through Paolo Toscanelli. These passages do not establish that Cusa invented concave spectacles, that he did so in 1451, or that it happened in Tyrol.

Commercial Evidence. By 1451, Florence had overtaken Venice as the primary manufacturer of high-quality spectacles, including concave lenses for myopes. This commercial dominance is further evidenced by a 1462 order from the Duke of Milan for three dozen spectacles, specifically requesting a dozen with concave lenses for distance vision, indicating the technology was established and in demand among the elite.