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The Original Bates Method, for correcting vision defects

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Studies of the Images of Purkinje        25
what are known as the images of Purkinje.1 If a small bright light, usually a candle, is held in front of and a little to one side of the eye, three images are seen: one bright and upright; another large, but less bright, and also upright; and a third small, bright and inverted. The first comes from the cornea, the transparent cover ing of the iris and pupil, and the other two from the lens, the upright one from the front and the inverted one from the back. The corneal reflection was known to the ancients, although its origin was not discovered till later; but the two reflections from the lens were first observed in 1823 by Purkinje; whence the trio of images is now associated with his name. Langenbeck examined these images with the naked eye, and reached the con clusion that during accommodation the middle one be came smaller than when the eye was at rest. And since an image reflected from a convex surface is diminished in proportion to the convexity of that surface, he con cluded that the front of the lens became more convex when the eye adjusted itself for near vision. Donders repeated the experiments of Langenbeck, but was un able to make any satisfactory observations. He pre dicted, however, that if the images were examined with a magnifier they would "show with certainty" whether the form of the lens changed during accommodation. Cramer,2 acting on this suggestion, examined the images as magnified from ten to twenty times, and thus con vinced himself that the one reflected from the front of the lens became considerably smaller during accommoda tion.
1 Johannes Evangelista von Purkinje (1787-1869). Professor of physiology at Breslau and Prague, and the discoverer of many important physiological facts.
2 Antonie C. Cramer (1822-1855). Dutch ophthalmologist.