Evidence of medieval spectacles found in book

On the blog Cultural Compass, an employee of the Harry Ransom Center chronicles the discovery of rare evidence of medieval eyeglasses, not in an illustration, but in the end pages of a book.

The blogger writes:

While conducting a survey of manuscript waste found in early printed books I noticed a faint reddish-brown impression of a pair of spectacles on the rear parchment endpapers of a copy of the Opera of Fr. Luigi di Granata.

The spectacles appear to be a pair of leather-framed eyeglasses dating to the late 15th century.