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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 36, Iss. 12 — Dec. 1, 1946
  • pp: 679–694

Report on Survey of Optical Aids for Subnormal Vision

V. J. ELLERBROCK  »View Author Affiliations

JOSA, Vol. 36, Issue 12, pp. 679-694 (1946)

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V. J. ELLERBROCK, "Report on Survey of Optical Aids for Subnormal Vision," J. Opt. Soc. Am. 36, 679-694 (1946)

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  1. The designation 20/20 indicates that test letters designed to subtend a visual angle of 5 minutes of arc when placed 20 feet from the subject became just legible. A visual acuity of 20/60 indicates that letters designed to subtend the same angle at 60 feet are legible only when viewed at a distance of 20 feet.
  2. A historical investigation of small magnifying aids for vision was made by Dr. M. von Rohr. The study covered a period of twenty-three years and was very thorough and exhaustive. Since practically none of the original references before 1910 are available in this country, the discussion of the proposed aids before 1910 is based principally on his series of articles which appeared in the Zeitschrift für ophthalnologische Optik (1916–27), entitled "Zur Entwicklung der Fernrohrbrille." Cf. Bibliography.
  3. When a very careful and thorough study is made of all the aids which have been suggested and manufactured to improve vision, it is apparent that only a very few have been specifically designed and produced for subnormal vision. There are several reasons that may account for this. One is that when the best possible design of a specific aid for subnormal vision is made, little or no room exists for further improvement unless a new optical material is discovered. Another factor is that the probable market for any subnormal vision aid until the last few years has been extremely small. Even at the present time a large number of eye specialists do not understand the principles of the visual aids which are available and consequently cannot prescribe them when they are indicated.
  4. Although many difficult problems are encountered in the design of telescopic spectacles, the most difficult and universal one is that of finding ways in which both high magnifications and large fields can be obtained. An increase in magnification or field immediately leads to large aberrations with the corresponding lack of definition of the image near the edges of the field. The history of these optical devices is a succession of designs which improve field definition and yet obtain higher magnification and larger fields. In this respect, theoretical designs are possible, but these prove impractical in actual manufacture because of weight, bulkiness, restriction of working distances, etc., as well as the factor of increased cost.
  5. Solid glass telescopes were known in Germany and the neighboring countries fron the 17th to the 19th century as Perspectivbrillen" or "Stöpsellinses." The small Galilean telescopes composed of separated lenses and used as spectacles were known as "Fernrohrbrillen."
  6. The importance of this contribution stems from the fact that many of the defects of the image formed by a refractive optical system, such as a telescope composed of lenses, do not exist in a reflecting optical system.
  7. The weight of a telescopic unit is tremendously reduced if a tubular mount does not have to be used.
  8. In order to facilitate the testing of individuals for telescopic spectacles, the Zeiss Company has produced sets containing telescopic elements of various refractive powers. When one desires to correct the refractive power of an individual, the telescopic element nearest that required to correct the ametropia is chosen, and then auxiliary lenses are added to correct the remainder.
  9. The Carl Zeiss Company produced two trial cases of telescopic spectacles, one for amblyopia and the other for myopia. The amblyopic set contains four telescopic elements having powers of 0, +3, -3, and -6 diopters. Sufficient auxiliary spherical and cylindrical lenses are provided to make up the exact refraction. Various reading attachments in two diopter steps are also provided. The myopic trial case contains 16 telescopic elements having powers of +3, 0, -3, and -6 diopters and then in two diopler steps to -30. As in the amblyopic set, adequate lenses are included so that the exact refractive error can be corrected, and plus lenses are supplied for various reading distances.
  10. These units were manufactured by the Kollmorgen Optical Company, Brooklyn, New York. Their size and weight were such that they could easily be mounted in a spectacle frame. Their clinical value, however, has been proven to be insignificant and their production has been discontinued.This same company manufactures two different types of spherical telescopic spectacle, one with a power of 1.7× and other with a power of 2.2×. The characteristics of these units are as follows: The increase in the field of view in comparison with the Zeiss units of approximately the same power is secured at the expense of the correction of the aberrations of the system. Lenses for the correction of the ametropia can be added by means of the sleeve attachment which fits over the ocular lens of the telescope. In the same manner reading additions can be added in front of the objective. The lenses are mount d in a light transparent plastic housing. A telescopic trial set composed of either two 2.2× or two 1.7× telescopic units, two 1½″ adapter rings, four assorted reading additions and a carrying case is manufactured and available at the present time.
  11. This type of telescopic unit was more fully described by Bettman and McNair in 1939 (cf. Bibliography). These two authors likewise presented and discussed cases of subnormal vision for which it had been prescribed.
  12. These units have not proved satisfactory, and are no longer manufactured by the Kollmorgen Optical Company. The principal objections, according to Dr. Kollmorgen of that company, were the excessive weight and the movement of objects when the head position is altered. He claims that 2.2× is the maximum that can be satisfactorily used as a head-borne device.
  13. According to Nordenson (cf. Bibliography, p. 406) careful experiments have shown that a magnification higher than 2.0× does not increase the possibility of observing details because the greater weight of the unit causes it unavoidably to oscillate with the pulsation of the small arteries and arterioles. This tremor, however insignificant it may seem, is nevertheless quite sufficient to obviate the effect of the greater magnification.
  14. It is known that the Theodore Hamblin Company, London, England, designed and is manufacturing telescopic spectacles. In a communication to the author, they make the claim that they have gone further in the development of these aids than Zeiss had done up to 1940. The difference between the two designs and the nature of the improvement has not been determined.
  15. For the sake of completeness in listing the optical aids for subnormal vision manufactured at the present time, two additional units need to be described. Neither is unique in design or construction. One, which was suggested by Dr. H. Eggers in 1933, consists of two lenses separated by a fixed distance and held in place by two small arms connected to the frames in which the lenses are mounted. A wire clip is provided so that the unit can be easily slipped over the ordinary spectacle lens. The whole unit folds together and can be conveniently carried in an ordinary spectacle case. The magnification produced is 1.36×, and can be used only for a fixed near distance. These units are marketed by the May Optical Company, New York City, New York. Another unit very similar to the one just described is marketed by Albert Aloe, an optician, of St. Louis, Missouri. The only essential difference from the Eggers unit is that the lenses are mounted in either analuminum or plastic housing, and is not collapsible. It is provided with a wire clip for fastening onto the spectacle lens. The basic magnification of the unit examined by the author was 1.36×. In both Aloe and Eggers units single crown lenses are used for both objective and eye-piece. The shapes of the lenses are such as to give maximum correction of the field.
  16. This aid is called "Fernrohrlupen" in the German literature. A literal translation of this term is confusing, and therefore, this aid as well as all others not used as spectacles will be called telescopic hand magnifiers.
  17. The historical survey up to 1910 was abstracted from the set of articles entitled "Zur Entwicklung der Fernrohrbrille" by M. von Rohr. Cf. Bibliography.
  18. Lenses designed for a near visual distance so that image and object are coincident though of different size.
  19. These lenses are called iseikonic. A literal translation from its Greek derivatives is "equal size."
  20. This binocular anomaly is called aniseikonia. It has been found that the presence of aniseikonia gives rise to symptoms similar to those resulting from a muscle imbalance or uncorrected refractive errors. Individuals with subnormal vision only rarely have the problem of fusing images of the two eyes, because one of the two images is usually so poorly defined that it is psychically suppressed.
  21. A telescopic trial set manufactured by this company is available at the present time. It consists of both 1.5× and 2.0× telescopic units as well as reading additions of various powers.
  22. The carrier lens can be ground so as to correct the refractive error of the user. The Zeiss Company was the first to suggest this unique mount for a telescopic unit. The first reference to it encountered in the literature was by J. Nordenson in 1924 (cf. Bibliography).
  23. Unless specific mention is otherwise made, it should be assumed that the lenses are made of glass.
  24. For example, the Bausch and Lomb Optical Company manufactures round, double convex, reading lenses from 2½″ to 5″ in diameter. The 2½″ lens has a power of 6.66 diopters and the 5″ reading lens 3.33 diopters. Approximately the same types are manufactured by the American Optical Company.
  25. The largest rectangular shaped lens used as an aid for reading which has been found recorded in the literature was 6.5 in. long and 3.25 in. wide (Stockwell, cf. Bibliography). It was used in a sight conservation class in Leeds, England. The power of the lens was +3.5 diopters and it was plano-convex in shape. It was mounted in a rigid frame and attached to a desk. A cowl for a lamp was built into the top part of the frame and served as a reflector.
  26. The Bausch and Lomb Optical Company markets only one size of this type of lens. It is 3″ in diameter and has a refractive power of 5.71 diopters. The Kollmorgen Optical Company manufactures units of this design having powers of 8× and 16× and markets them under the trade name of "Microvisor." The lenses are mounted in a transparent plastic housing 36 mm in diameter. A flange on one edge of the housing permits the unit to be conveniently mounted in a spectacle frame.
  27. The magnification of a reading (thin) lens is given by, [Equation], in which ƒ represents the focal length of the lens; h, the distance of the lens from the eye, and p, the distance of the object from the eye. When ƒ = p-h, the magnification is M = p/ƒ.
  28. The Carl Zeiss Company, markets two sizes of this type of reading lens. One is 1½″ in diameter and the other 2 3/8″. The Univis Lens Company makes available the same type of lens as the Zeiss Company. In addition they have introduced another one in plastic (methyl methacrylate) which has the form illustrated in 8E. The diameter of the Univis units on the flat surface are 1″ and 1.5″.
  29. The Carl Zeiss Company markets three aspherical reading lenses having the following characteristics: The aspherical curve is ground on only one surface. The lens is composed of a single glass element.
  30. An example is the one marketed under te trade name, "magni focuser." It consists of two +5.00 diopter lenses fixed in a plastic mount with their optical centers having a 38.0-mm separation. When properly worn, the lenses are approximately 50 mm from the eyes.
  31. This device is not commercially produced. A schematic drawing of it can be found in the report of the survey submitted to the Committee on Sensory Aids.
  32. In the last few years there has been an increase in the use of contact lenses; they are being manufactured by a number of American and European firms.
  33. Unfortunately, no information can be found concerning the dimensions of the tubes used.
  34. The American Ecyclopedia of Ophthalmology, Vol. XVII, p. 13, 473.
  35. Instruments constructed on the optical principles illustrated in Fig. 40, A and B, are commercially produced and known under various trade names such as Epidiascope, Balopticon, and Delineascope.
  36. H. Wolff (1918), Johannes Raefler (1919), H. Gradle ani J. Stein (1924), L. Mayer (1927), A. Brunner (1930), and W. Feinbloom (1934).
  37. This is true since the reading add which must be used for near with a telescopic spectacle or hand magnifier produces a magnification.
  38. It should be pointed out that there is some question as to the reliability of these results. The percentage of patients (46 percent), who, Feinbloom claims, can be satisfactorily aided by the use of telescopic spectacles is very high. According to the opinions of the ophthalmologists and optometrists who have not made a study of this problem, not more than 15 percent can be given satisfactory aid. Many estimate the percentage to be even as low as 1 percent or 2 percent.
  39. Obviously, any controversy about the percentage of patients aided might be a result of the lack of understanding of the term "satisfactorily aided." As it is used here, it means at least 20/50 vision for near. Likewise, the term implies that vision with the aided eye can be achieved without undue discomfort and annoyance from the mechanical or optical device employed.
  40. An interesting comment by Leo Mayer (cf. Bibliography) in this regard is "I shall not try to explain the methods of fitting telescopic spectacles; suffice it to say that only with many trials, constant urging, and an unlimited amount of patience is one able even to attempt this mode of increasing sight." In another report he stated that "… no amount of case reports or explanation could in any measure bring to you the knowledge of the amount of patience, care and even coercion necessary to urge the patient to wear telescopic spectacles."
  41. Any survey of this nature necessarily entails a great obligation to the individuals and organizations who gave information, expressed opinions, and made recommendations. The author wishes to acknowledge the assistance he obtained.
  42. The free-vorking disLanice is defiled as the distance from the object surface to the front surface of the telescopic unit.
  43. The ophthalmologist Mayer will not give out-of-town patients subnormal vision aids for trial, but requires them to buy it outright if it improves their vision to his satisfaction and providing, of course, that the patients are able to afford the cost. He has found that if a person has invested in an aid, there is a greater likelihood that he will attempt to use it. [Arch. Ophth. 2, 316 (1929).]
  44. It is unfortunate that so few ophthalmologists and optometrists have had training in the use of telescopic spectacles. Without doubt this fact partially accounts for the failure of the eye professions to prescribe them.
  45. Little or no information is at hand as to whether or not telescopic trial sets are available at the various eye centers. To what extent individuals who are in need of the aids are tested and equipped with them is also not known. How-ever, there is reason to suspect that such sets are only fortuitously available at a few scattered places.
  46. This policy is the result of the recommendations of the in-service Rehabilitation Committee set up by President Roosevelt during World War II.
  47. C. Berens and W. Hathaway, "Sight saving classes," Arch. Opth. 18, 845–849 (1935).
  48. For the definitions of total, economic, vocational, and educational blindness, see E. Jackson, A. C. Snell, and H. S. Gradle, "Report of the Committee on Definition of Blindness," J.A.M.A., 1032, 1445–1446 (1934).
  49. Bender, Imus, et al., Dartmouth College Publications (1942), pp. 323–32.
  50. The Zeiss telescopic hand magnifiers and the Kollmorgen Microvisors produce magnifications to 10×. However, the very small visual field makes them practically useless for reading.

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