The Wikipedia definition is: “Glasses, also known as eyeglasses or spectacles, are devices consisting of lenses mounted in a frame that holds them in front of a person’s eyes.” The French called early versions pince-nez which literally means ‘pinch the nose.’ The term spectacles was the name given when arms were added to the lenses so that the ears could provide more comfortable support than a squashed nose.
The word spectacle may have been adapted from the Latin words specere (to look at) or spectare (to observe). The word glasses may have evolved from the word spyglass, the name often given to telescopes.
Magnifying glasses had been around for a very long time. However the relationship between the shape of a lens and its magnifying qualities was a more recent discovery. The scientist, mathematician, astronomer and philosopher Ibn al-Haitham (965-1039) was the first to recognise the correlation between the curved surface of a semi-spherical lens and its powers of magnification when he published his seven volume thesis The Book of Optics.
Robert Grosseteste (c. 1175-1253) the English statesman, scientist, theologian and philosopher became interested in experiments with magnifying lenses, and passed this interest onto his most famous pupil, Roger Bacon (1213 – 1292). Bacon made the first recorded reference to the magnifying properties of lenses in 1262. He was a young lecturer at Oxford University where he carried out experiments with lenses and mirrors. In 1268 he suggested that properly shaped lenses might assist people with low vison.
Glasses appeared first in Florence about 1280 and their use spread rapidly across Europe. Credit for the invention is usually given to a monk called Alessandro di Spina who died in the Italian city of Pisa in 1313. Salvino degli Armati, is also credited as having some involvement. Although I have read several accounts that suggest his involvement was a hoax.
It took another three hundred years before anyone was able to explain why glasses actually worked. In 1604 the work of the German astronomer, mathematician and astrologer Johannes Kepler (1571 – 1630) was published. In the course of his astronomical investigations Keppler provided a correct explanation of vision and the functions of the pupil, cornea and retina.
In 1784 Benjamin Franklin (1706 – 1790) invented bifocals. Benjamin suffered from both myopia (short-sightedness) and presbyopia (reduced ability with age to clearly focus on close objects). In his invention the two lens sections were held by the frame; the middle and lower portion of the lens having different focal lengths.