Essential for reading and writing, and an important factor in the spread of literacy, spectacles are thought to have been invented in thirteenth century Europe; however, their inventor is unknown. Various unsubstantiated theories were proposed over the centuries concerning possible inventors—none supported by satisfactory evidence. Some of the theories are mentioned in the Wikipedia article on Glasses.
Other contenders and snippets of evidence regarding possible inventors are listed on the London College of Optometrists web page on the Invention of Spectacles. Even though the name of the inventor or inventors of spectacles may never be confirmed, there is sufficient reason to believe that spectacles were invented toward the end of the thirteenth century, and that they became more widely used as the fourteenth century advanced.
A Venetian ordinance dated Aprl 2, 1300 indicates that lenses were then widely enough used for reading to have legal consequences:
"Venice was a major centre of glass production, and by the end of the thirteenth century eyeglasses had certainly become an object of general use there, as we can tell from an ordinance dated 2 April 1300 aimed at makers of glass and crystal. It prohibited them from perpetrating a fraud that must have become widespread: 'acquiring or causing to acquired, and selling or causing to be sold, ordinary lenses of colourless glass, under the pretense that they are crystal, for example buttons, handles, discs for kegs and for the eyes ('roidi de botacelis et da ogli'), tablets for altar pictures and crosses, and magnifying glasses ('lapides ad legendum'). The penalty was a fine and the smashing of the fraudulent object. The precise distinction made in the document between eyeglasses and magnifying glasses establishes clearly just what each of the named objects is, and since words preserve their own past like fossils preserved in amber, I note that the term Brille, which means eyeglasses in German, is derived from berillium, the medieval latin word for crystal (Frugoni, Inventions of the Middle Ages  7 and footnote 25).