The On-Line Museum and Encyclopedia of Vision Aids.
Three months after the death of Francesco Sforza, his son and successor, Galeazzo Maria, wrote on June 13, 1466, to the same ambassador requesting two hundred pairs of eyeglasses. Original in Milan, Archivio di Stato, Archivio Sforzesco Ducale, Registri delle Missive, Reg. 77, fol. 89v , Microfilm Collection Reel No. 1176. The text of this letter follows.
Because we earnestly desire to have the eyeglasses as noted in the list here enclosed, we desire that upon receipt of this letter you should endeavor to acquire them perfectly made according to the ages specified in the aforesaid list. Send them in a box, well arranged and separated with attached labels for each category, so that when we receive them we shall be able to distinguish one category from the other. Inform us of their cost so that we can make provision for the payment. Milan, 13 June 1466.
XV pairs of eyeglasses for ages 30, 35, 40, 45, 50, (55 crossed out), thin [fini]
Item, XV pairs of eyeglasses for ages 40, 45, 50, 55, 60, 65, 70.
Item, X pairs of eyeglasses for medium vision for the young
Item, X pairs for distant [vision] for the young.