Abstract

Early attempts to provide optical magnification to compensate for subnormal visual acuity used small galilean telescopes, mounted in spectacle frames, giving magnifications ranging from 1.3 to 3×. They were seldom helpful in distance vision because of the restricted field, change of apparent distance, and inadequate magnification. Many used them only for reading, and obtained additional magnification from a reading cap of high dioptric power which permitted a close viewing distance. After about 1955, the interest in telescopic magnifiers was almost entirely replaced by two other developments. One emphasized the use of simple reading spectacles of high power. A second involved the search for inexpensive optical aids such as jeweller’s loupes, thread counters, magnifiers for inspection of coins or stamps, and similar devices developed for the normal eye. Trial-and-error prescription of these devices as reading aids was later superseded by more-systematic procedures based on measurement and classification of the available aids as to magnifying power and type. This led to the development of new optical aids to supplement those already available. Examination procedures were also devised to assist in selection of aids of the required power and type for each user.

© 1972 Optical Society of America

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