"Nearly three thousand years ago, the ancient Egyptians knew that a glass lens can make an object look bigger. Nero... is said to have looked through an emerald to watch his gladiators fighting... By the ninth century, people were using 'reading stones' to assist their failing eyesight. These were polished lumps of clear glass, rounded on one side and flat on the other; you sat them on top of the document you were trying to read... The first true spectacles were almost certainly invented in Italy between 1280 and 1300. They acted like a magnifying glass and corrected long-sightedness; it would be another 300 years before lenses able to correct short-sightedness would be developed, in part because these were much harder to make. Johannes Kepler (astronomer, astrologer and mathematician) was the first to explain how convex and concave lenses corrected eyesight. ...lenses were (and still are) made by grinding glass using various types of abrasive material, which in Kepler's time were already being used by jewellers."