Originally intended to be for temporary wear, to correct permanently the focus of the eyes, spectacles, as they were then known, or eyeglasses, were invented sometime between 1280 A.D. and 1300 A.D. in Italy (they seem to have been invented independently, by two different persons, in a very short period of time). The eyeglasses were the opposite of today’s glasses, in that the lens was ground to force the eyes into focusing to counteract the effect of the lens, thus retraining the muscles of the eye (so someone nearsighted would be given a lens that would be given to a farsighted person today).
Although the phenomenon of using lenses, whether water in a globe, or ground from glass, had been known since ancient times, the medieval genius was in devising a way to put these lenses into everyday use, meant for common wear, and also to use the lenses not only to help the person see better, but to actually permanently retrain the muscles of the eye to focus correctly.
Although spectacles were meant to be used regularly, they were either held in place by one’s hands, or as in pince-nez, by exerting pressure on the nose, so that they did not slip off. It took almost five hundred years for someone to put ear-pieces on the frames, and thus make an improvement to this important medieval invention.
The Middle Ages also saw the invention of sunglasses, to protect the eyes from glare, but the sunglasses were not combined with corrective lenses in the Middle Ages (one wonders why!).