Proper glasses should be selected and carefully fitted to the eyes whenever they are affected by old-sight, long-sight, short-sight, or astigmatism. A competent physician or an oculist should be consulted in every case with reference to the wearing of spectacles, and their adaptation to the eye. Spectacle venders who travel about the country should not be patronized under any circumstances. Glasses made of flint glass, or of what is known as rock crystal or Brazilian quartz, are the best. The last variety is known as "pebble" glass. The only advantage which it has over other glasses is its hardness. Spectacles should also be perfectly clear and free from irregularities in the glass.

It is sometimes advantageous to wear glasses for the purpose of protecting the eye from mechanical injury, when they are much exposed, as in certain trades. Colored glasses, as London smoke, green or blue glasses, are also necessary in many cases to protect the eye from intense light. Protection of this sort is very necessary for travelers in snowy regions, whose eyes are likely to suffer from the dazzling brightness of the reflected sunlight, producing an affection known as snow blindness. For the convenience of persons who are obliged to use two sets of glasses, one for viewing near objects, the other for distant vision, spectacles are sometimes made in which the lower part of the lenses is ground so as to be adapted to near vision, while the upper part is adapted to distant vision. These are known as Franklin glasses because they were invented and first used by Benjamin Franklin The kind of frame to be employed is wholly a matter of taste.