Defects of refraction in the eye and in lenses have been named from the points of view of those who first observed them. There were spherical convex lenses two thousand years ago, called "burning glasses" because of their use to light fires. The 4 D. convex lens of rock crystal, found by Layard in the ruins of Nineveh, may have been called a "sight saver" by the man who made it, when he found that it lengthened his years of useful work. The Greeks, who studied and watched the symmetry of the face, naturally called myopia the near-sightedness they tried to overcome by narrowing the space between the lids. Presbyopia was the name for the defect of sight that came with age and caused crow's feet at the corners of the eyes of old men.
The lens grinders found surfaces departing from the shapes they tried to produce, and even