Spectacles, for the purpose of aiding the sight when impaired by age or otherwise (see EYE), are commonly said to have been invented during the 13th century. The merit is variously attributed to Alessandro di Spina, a monk who died at Pisa in 1313, and to Salvino degli Anati, who died at Florence in 1317; but spectacles seem to be referred to by the Arab writer Alhazen (11th century) and by Roger Bacon (c. 1214-94). In 1482 there were spectacle-makers at Nuremberg. At first spectacles were exceedingly clumsy, both in the lenses themselves and also in their frames; and very little improvement took place in them until the beginning of the 19th century, when light metal frames were introduced instead of the cumbersome horn or tortoiseshell mountings, which are still occasionally seen, and have obtained the name of goggles. So skilful are the workmen of Wolverhampton, where they are chiefly made, in the manufacture of steel frames that some of exquisite workmanship are now turned out, which, with their lenses complete, are under a quarter of an ounce in weight. They have consequently displaced gold, silver, and all other materials, when comfort and effectiveness are desired. The lenses themselves are nearly always made of the best optical glass, and by the best makers are ground with extreme care. Many profess to be made of 'pebbles' or rock-crystal; but lenses really made of that material are exceedingly rare and have no real advantage over good glass. The spectacle-frame ought to be so fitted that the optic axes of the lenses shall coincide with those of the eyes; otherwise there is a strain on the eyes.
It is most important that the glasses worn should be properly selected, otherwise they may do much harm. In cases of Astigmatism (q.v.), and those where the two eyes are different, competent medical advice should always be sought. In simple myopia (short-sight) and hypermetropia (long-sight; see EYE, Vol. IV. p. 515) the general principles of selection are less complex, though their proper application is often a difficult matter. In short-sight the glasses (concave) used should be the weakest with which distant objects are clearly seen, or somewhat weaker; in long-sight the glasses (convex) should be the strongest with which distant objects are clearly seen; for reading and near work still stronger glasses are often required. In presbyopia or old-sight (Vol. IV. p. 512) the glasses should be of such a strength as to enable print to be comfortably read at about 10 inches from the eyes.