Report on Survey of Optical Aids for Subnormal Vision

Journal of the

OPTICAL SOCIETYof AMERICA

VOLUME 36, NUMBER 12 DECEMBER, 1946

Report on Survey of Optical Aids for Subnormal Vision*

V. J. ELLERBROCKResearch Division, The Dartmouth Eye Institute, Hanover, New Hampshire

(Received September 23, 1946)

I. INTRODUCTION

AN individual is said to have subnormalvision if when fully corrected for refractive

errors with spectacles, his visual acuity is stillless than normal, i.e., less than the Snellen20/20.1 However, individuals with visual acuitiesslightly poorer than 20/20 are not significantlyhandicapped. This fact is recognized by theAmerican Medical Association, for which a visualacuity of 20/60 represents a loss of vision ofonly 25 percent. Hence it is usual to considersubnormal vision as representing a visual acuityof 20/70 or less. On the other hand, personswhose visual acuity is 20/200 and less are con-sidered legally blind. The survey of optical de-vices for subnormal vision reported in this paperwill be concerned with devices for persons who,when fully corrected, have visual acuities be-tween 20/70 and 20/200.

There is little difference in the causes of sub-normal vision for large unselected groups. Astatistical tabulation of the reports of six in-vestigations is given in Table I.

* This paper is a condensation of a report submitted tothe Committee on Sensory Aids of the Office of ScientificResearch and Development, and represents the preliminarystep in a broader program of studying optical devices thatcan be used by persons with subnormal vision.

' The designation 20/20 indicates that test letters de-signed to subtend a visual angle of 5 minutes of arc whenplaced 20 feet from the subject became just legible.A visual acuity of 20/60 indicates that letters designed tosubtend the same angle at 60 feet are legible only whenviewed at a distance of 20 feet.

Statistics of the causes of subnormal visiondue to injuries received by the armed forces dur-ing World War II are not yet available. Fromstatistics compiled as a result of injuries incurredduring World War I, it was found that the dis-tribution of causes was approximately the samefor an unselected group of civilians as for anapproximate equal number of soldiers (Raefler,cf. Bibliography).

II. HISTORICAL BACKGROUND OF OPTICALAIDS FOR SUBNORMAL VISION

In order to evaluate the aids which are manu-factured at present for subnormal vision, it isnecessary to consider them in the light of theirhistorical development. 3

TABLE I. A statistical analysis of the causes of subnormavision from six separate investigations.*

Gradleand Brun- Fein-

Wolff Raefiler Stein Mayer ner bloom Av.

Retinal and chor- 17% 40% 28% 34% 34% 36% 31%oidal involvement

Lens involvement 2% 5% 34% 22% 22% 23% 16%Optic nerve 7% 16% 13% 15% 11% 13% 12%Cornea 42% 19% 6% 8% 11% 11% 16%Physical anomalies 20% 9% 13% 13% 22% 9% 14%Glaucoma 2% 7% 8% 3%Cause not specified 12% 9% 6% 5%Number of cases 41 149 15 45 19 298 -

* This table was taken from a report by Feinbloom, to which thedata of Wolff and Raefler have been added.

2 A historical investigation of small magnifying aids forvision was made by Dr. M. von Rohr. The study covered aperiod of twenty-three years and was very thorough andexhaustive. Since practically none of the original refer-

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V. J. ELLERBROCK

X CONCAVE' MIRROR

z ~ ~ ~ ~ __CONVEXA-MIRROR

FIG. 1. Illustration of the effect of Dixon's mirror telescopeon a parallel bundle of incident rays.

A. Telescopic Devices

Perhaps the foremost of these aids are variousforms of the Galilean telescope. Though bothGalilean and terrestrial telescopes have, beenused for the aid of subnormal vision, only Gali-lean telescopes have been successfully used asspectacles. Because the principal use of terrestrialtelescopes is limited, they can best be classifiedas a telescopic aid for reading only.

1. Telescopic Spectacles4

Historically, there were two distinct designsof the Galilean telescope for use as spectacles.In the one the interspace between the objectiveand eyepiece was glass and in the other it was air.

ences before 1910 are available in this country, the dis-cussion of the proposed aids before 1910 is based principallyon his series of articles which appeared in the Zeitschrift

four ophthalnologische Optik (1916-27), entitled "Zur Ent-wicklung der Fernrohrbrille." Cf. Bibliography.

I When a very careful and thorough study is made of allthe aids which have been suggested and manufactured toimprove vision, it is apparent that only a very few havebeen specifically designed and produced for subnormalvision. There are several reasons that may account forthis. One is that when the best possible design of a specificaid for subnormal vision is made, little or no room existsfor further improvement unless a new optical material isdiscovered. Another factor is that the probable marketfor any subnormal vision aid until the last few years hasbeen extremely small. Even at the present time a largenumber of eye specialists do not understand the principlesof the visual aids which are available and consequentlycannot prescribe them when they are indicated.

I Although many difficult problems are encountered inthe design of telescopic spectacles, the most difficult anduniversal one is that of finding ways in which both highmagnifications and large fields can be obtained. An in-crease in magnification or field immediately leads to largeaberrations with the corresponding lack of definition ofthe image near the edges of the field. The history of theseoptical devices is a succession of designs which improvefield definition and yet obtain higher magnification andlarger fields. In this respect, theoretical designs are possible,but these prove impractical in actual manufacture becauseof weight, bulkiness, restriction of working distances, etc.,as well as the factor of increased cost.

In the former case, a solid piece of glass wasground so as to have a convex surface on theside facing the incident light, and on the otherside, a concave surface of such curvature thatthe unit would be afocal.5 These will be referredto as afocal magnifying lenses, while the tele-scopes consisting of lenses with an air interspacewill be called telescopic spectacles, as in currentusage.

The first major contribution toment of telescopic spectacles was

the develop-made by F.

Eschinardi, a Jesuit priest, in 1667. He suggested

A. DILLENSEGER'SMOUNT

B. CHIESA'S MOUNT

FIG. 2. Drawings A and B illustrate two of the manymodifications for the mechanical mount of the objectiveand eyepiece lenses.

I Solid glass telescopes were known in Germany and theneighboring countries fron the 17th to the 19th centuryas Perspectivbrillen" or "St6psellinses." The small Gali-lean telescopes composed of separated lenses and used asspectacles were known as "Fernrohrbrillen."

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REPORT ON SURVEY OF OPTICAL AIDS

that a Galilean telescope be used for near vision(50 cm) for an individual who had a myopia of6'D. The magnification was approximately 110percent or 2.11 X. Eschinardi recognized thepossibility of changing the separation of the twoelements in the telescope so that it could beused for different visual distances. He recom-mended that in the event that this could not beaccomplished easily, two sets of telescopic spec-tacles, one for distance and the other for near,should be provided.

By 1695 Chr. Huygens in his Dioptrica hadspecified the precise rule to be used for the ad-justment'of a Dutch telescope to the refractivecondition of the eye, although the mathematicalrelationship had been derived some years pre-viously. In 1686 J. Zahn described a mechanicaladjusting device whereby the distance betweenthe lenses of a telescope could be changed.

The next significant contribution was made byH. Dixon in 1786. He proposed using two spheri-cal mirrors arranged as shown in Fig. 1.6 Thewhole device was mounted in a spectacle frame.The suggestion was made, that the distance be-tween the mirrors be varied to accommodatevarious refractive errors.

By 1846 C. A. Steinheil and L. Seidel had de-signed a small Galilean telescope with a magni-fication of 2 X which had an excellent field, littleor no chromatic aberration, and was free fromspherical aberration and distortion of the imageover the whole field. However, units having aweaker magnification, i.e., 1.2X to 1.3X, werechosen for commercial manufacture. In the com-mercial announcements, emphasis was placed onthe very large corrected field of these units.

Giron and Mitaine in 1840 applied for a patentto protect an invention of a simple opera glass.The lens elements of their unit had no tubularsupport, but it could' be adjusted for variousrefractive conditions as well as for distant andnear vision.7 When the lenses were pushed to-gether, the glasses could be folded into a verycompact unit. In 1849, A. Dillenseger designed a

6 The importance of this contribution stems from thefact that many of the defects of the image formed by arefractive optical system, such as a telescope composedof lenses, do not exist in a reflecting optical system.

7 The weight of a telescopic unit is tremendously re-duced if a tubular mount does not have to be used.

FIG. 3. Photograph of two pairs of Zeiss telescopicspectacles and attachments. The reading attachment isdesignated by a, and the attachment for the correction ofan ametropia by b.

color-free theater spectacle consisting of anachromatic objective and single lens eyepiece.The mount was of light-weight construction.Like the Mitaine spectacle, the, distance betweenthe lenses could be varied and the whole unitfolded into a compact case (Fig. 2A). The achro-matic objective was later discarded and replacedby a simple converging lens. R. Chiesas in 1894proposed a further modification of the mechanicalmount, as illustrated in Fig. 2B.

The first to suggest the use of a correcteddoublet eyepiece for telescopic spectacles ap-pears to be M. von Rohr. Like Steinheil andSeidel he designed a unit which reduced theoptical defects of the image to a minimum andyet gave a relatively large visual field. How hisdesign differed from that of his predecessors isnot entirely clear. In all probability, since adoublet eyepiece was used and different kinds ofglass were more available in 1909 than 1846 todesign corrected lenses, von Rohr's design wassuperior. The magnifications provided were 1.3 Xand 1.8 X. The design required a fixed separationof the objective and eyepiece lenses if the variousaberrations calculated for one object distancewere to be kept at a minimum for other dis-tances. A machined mount of light, sturdy,German silver was used. To accommodate dif-ferent visual distances, slip-over plus lensescould be attached to the front of the objective.Moreover, refractive errors of the eye could becorrected by means of slip-over lenses attached

:; . n d :: t

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V. J. ELLERBROCK

Z t--tI Z'

C \

FIG. 4. Mifiller's telescopic spectacle invented in 1912.

to the eyepiece.8 9 The whole unit was rigidlymounted in a metal spectacle frame (Fig. 3). Ifbinocular vision at both far and near was de-sired, two sets of telescopic spectacles wouldhave to be employed. If binocular vision wereto be used for distant vision only, a frosted glasscap to be slipped over the eyepiece of the unusedtelescope was provided.

If a judgment had to be made as to whetherthe optical or mechanical design of the Zeisstelescopic spectacles were the more important,in all probability the weight of the evidencewould favor the latter. However, it should beremembered that such a critical judgment ispossible only because of the thoroughness withwhich von Rohr studied this problem.

C. Muller, in 1912, altered the mount of thetelescopic spectacles to reduce weight. The de-sign consisted of a small objective, a, shown inFig. 4, held in position in front of the eyepieceby arm, b. The ocular is a small corrected lens,cemented or fused into the countersink, c, of theophthalmic lens. The advantage of this designis that it is light in weight and permits peripheralvision through the lens surrounding the ocular

8 In order to facilitate the testing of individuals for tele-scopic spectacles, the Zeiss Company has produced setscontaining telescopic elements of various refractive powers.When one desires to correct the refractive power of anindividual, the telescopic element nearest that required tocorrect the ametropia is chosen, and then auxiliary lensesare added to correct the remainder.

I The Carl Zeiss Company produced two trial cases oftelescopic spectacles, one for amblyopia and the other formyopia. The amblyopic set contains four telescopic ele-ments having powers of 0, +3, -3, and -6 diopters.Sufficient auxiliary spherical and cylindrical lenses areprovided to make up the exact refraction. Various readingattachments in two diopter steps are also provided. Themyopic trial case contains 16. telescopic elements havingpowers of +3, 0, -3, and -6 diopters and then in twodiopler steps to -30. As in the ablyopic set, adequatelenses are included so that the exact refractive error canbe corrected, and plus lenses are supplied for variousreading distances.

of the telescope. No reference can be found con-cerning the field properties secured with such aunit.

An attempt to provide normal localization ofobjects seen through a telescopic spectacle wasmade by Feinbloom in 1930. He designed ameridional magnifying telescopic unit having apower of 1.8X in the horizontal meridian and1.3X in the vertical meridian. A square objectseen through such a unit would appear as a rec-tangle and would be subjectively localized inspace at approximately the same position as theobject. Such a unit would be of most use indistant vision, especially when walking, etc.' 0

The field properties of these units are fair.Independently, Dallos and Dittmer in 1936

suggested the use of a contact lens for the eye-piece of a telescopic spectacle. The objectiveconsisted of an ordinary plus lens, such as theconventional cataract lens. The contact lenscould be used to produce varying negativepowers. Were the front surface of the contactlens flat, the corneal power would be eliminatedin the refraction of the rays of light entering theeye. Since the average refraction of the cornea isabout +45 diopters, such a contact lens wouldproduce an eyepiece in a telescopic combinationhaving an effective power of -45 diopters. Then,if a plus lens at a fixed distance in front of theeye is used as the objective of the telescope, andof such power that parallel incident rays of lightwill be focused on the retina, a telescopic unit

10 These units were manufactured by the KollmorgenOptical Company, Brooklyn, New York. Their size andweight were such that they could easily be mounted in aspectacle frame. Their clinical value, however, has beenproven to be insignificant and their production has been dis-continued.

This same company manufactures two different types ofspherical telescopic spectacle, one with a power of 1.7Xand other with a power of 2.2X. The characteristics ofthese units are as follows:

Field of Diameter Over-allLinear M view objective length Weight

2.2 X 220 26 mm 26 mm 0.75 oz.1.7 X 350 36 mm 22 mm 1.00 oz.

The increase in the field of view in comparison with theZeiss units of approximately the same power is secured atthe expense of the correction of the aberrations of thesystem. Lenses for the correction of the ametropia can beadded by means of the sleeve attachment which fits overthe ocular lens of the telescope. In the same mannerreading additions can be added in front of the objective.The lenses are mounted in a light transparent plastichousing. A telescopic trial set composed of either two2.2X or two 1.7X telescopic units, two 1k" adapter rings,four assorted reading additions and a carrying case ismanufactured and available at the present time.

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would be produced." Under conditions of re-laxed accommodation the magnification pro-duced would be:

M= (FC-Fe) /F.,

where F designates the power of the corneawithout the contact lens (diopters); Fe thepower of the cornea with the contact lens; andF6 the power of the objective.

In place of the cataract lens as the objectiveof a telescopic system, it is conceivable that aplus lens might be attached directly to the con-tact lens. Accordingly, the corneal section of thecontact lens then becomes a compound opticalsystem. This idea was actually patented by Fein-bloom in 1940. Figure 5 illustrates a cross sec-tion of such an optical system. The claim ismade that the difficulties of restriction of thefield of view and those due to the obliquebundles of rays can be largely overcome by thismethod. The advantage of this technique lies inthe fact that the compound optical system moveswith the eye, and consequently the line of sightis always substantially coincident with the op-tical axis.

A contribution to the design of telescopicspectacles for use at both distant and nearvision was made by Tait and Neil in 1936. Theyrecommended the use of ordinary ophthalmiclenses to correct the refractive error. On theocular surface of this lens are ground two smallcountersinks which serve as the ocular lenselements of the telescopes, one in the straightforward position and the other in the readingposition. The objectives are small, thin positivelenses cemented to a large carrier lens. Thiscarrier lens is mounted at a distance in front ofthe eyepiece lens so that the telescopic combina-tion is either afocal or equal to the refractiveerror of the eye. For reading, the power of thesmall cemented leifs has to be increased in aninverse ratio to the reading distance. The claimis made that with discreet choice of curves ofboth objective and eyepiece, good field propertiesare secured. The authors likewise claim thatlittle or no difficulty is encountered because ofthe reduced field of vision as compared with

"This type of telescopic unit was more fully describedby Bettman and McNair in 1939 (cf. Bibliography). Thesetwo authors likewise presented and discussed cases ofsubnormal vision for which it had been prescribed.

that secured with the Zeiss telescopic spectacleor a similar telescopic unit of equal magnification.

In an attempt to secure a larger magnificationin a telescopic spectacle, Feinbloom, in 1941,designed a unit consisting of a doublet objectivelens and a single ocular lens. The system wasmounted in a transparent plastic shell and wassmall enough to be fitted into an ordinary eye-glass frame. The magnification produced was3.0 X. The exit pupil was relatively large, per-mitting its use in cases having marked nys-tagmus.12 , 13

It is possible that omissions have been madein the historical study of the development oftelescopic spectacles.' 4 Those contributions whichwere found to be unessential have not beenincluded.15

FIG. 5. Schematic drawing of the Feinbloom contacttelescopic unit. The two surfaces separated by the inter-space m are in contact when the unit is used.

12 These units have not proved satisfactory, and are nolonger manufactured by the Kollmorgen Optical Com-pany. The principal objections, according to Dr. Koll-morgen of that company, were the excessive weight andthe movement of objects when the head position is altered.He claims that 2.2 X is the maximum that can be satis-factorily used as a head-borne device.

13 According to Nordenson (cf. Bibliography, p. 406)careful experiments have shown that a magnificationhigher than 2.0 X does not increase the possibility ofobserving details because the greater weight of the unitcauses it unavoidably to oscillate with the pulsation of thesmall arteries and arterioles. This tremor, however in-significant it may seem, is nevertheless quite sufficientto obviate the effect of the greater magnification.

14 It is known that the Theodore Hamblin Company,London, England, designed and is manufacturing telescopicspectacles. In a communication to the author, they makethe claim that they have gone further in the developmentof these aids than Zeiss had done up to 1940. The differencebetween the two designs and the nature of the improve-ment has not been determined.

1" For the sake of completeness in listing the optical aidsfor subnormal vision manufactured at the present time,two additional units need to be described. Neither isunique in design or construction. One, which was sug-gested by Dr. H. Eggers in 1933, consists of two lensesseparated by a fixed distance and held in place by two

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V. J. ELLERBROCK

2. Telescopic Aids other than ThoseUsed as Spectacles

A detailed historical survey of the develop-ment of all types of telescopic aids other thanthose used as spectacles will be of little use inunderstanding those being employed at the pres-ent time for the aid of subnormal vision. How-ever, a brief resume of the historical highlightsmay prove of interest.

Seventeen years after H. Lipperhey made thefirst telescope in 1608, D. Chorez constructed avery small one about 3 inches in length. Pre-sumably this was of Dutch design and was usedas a hand telescope. The earliest evidence avail-able that these devices were used as aids forpoor vision is from A. Kirchner in 1645 andJ. Zahn in 1686.

Many improvements in lorgnettes or operaglasses were made in the eighteenth and nine-teenth centuries. These were generally con-structed on the Dutch design and were usedprincipally for distant vision.

It is impossible to trace the first use of thehand telescope to aid subnormal vision for neartasks. The oldest reference that can be foundconcerns a telescopic magnifier designed by theZeiss Company, in 1911. This company wasprimarily interested in providing high magnifica-tion with a large reading distance to aid in-dividuals with very poor vision. To attain theseobjectives, a telescopic unit designed on theprinciple of the terrestrial telescope was de-veloped. Three magnifications were available,3X, 6X, and 8X; or 200, 500, and 700 percent,respectively. The very small fields secured withthese magnifications required the use of a rigidstand which could be moved over the print or a

small arms connected to the frames in which the lensesare mounted. A wire clip is provided so that the unitcan be easily slipped over the ordinary spectacle lens.The whole unit folds together and can be convenientlycarried in an ordinary spectacle case. The magnificationproduced is 1.36 X, and can be used only for a fixed near dis-tance. These units are marketed by the May Optical Com-pany, New York City, New York. Another unit very similarto the one just described is marketed by Albert Aloe, an opti-cian, of St. Louis, Missouri. The only essential difference fromthe Eggers unit is that the lenses are mounted in either analuminum or plastic housing, and is not collapsible. It isprovided with a wire clip for fastening onto the spectaclelens. The basic magnification of the unit examined bythe author was 1.36X. In both Aloe and Eggers unitssingle crown lenses are used for both objective and eye-piece. The shapes of the lenses are such as to give maximumcorrection of the field.

A .

FIG. 6. A photograph of a Zeiss telescopic hand mag-nifier mounted on a movable reading rack is shownabove (A). In the lower illustration (B) the magnifier ismounted on a "U foot" stand.

stationary stand used with a device to move theprinted matter in front of the telescope. A com-plete set consisting of telescopes, stand, andmovable rack was manufactured by this com-pany (Fig. 6).1'

The original design and construction of theZeiss unit was excellent. However, inasmuch asits users obtained only a limited amount of suc-cess with it, no other company or individualsince then has attempted to design and manu-facture a similar device.

3. Afocal J1M[agnifying Lenses

Rene Descartes, in 1637,'7 was the first to con-cern himself with the design of an afocal magni-

16 This aid is called "Fernrohrlupen" in the Germanliterature. A literal translation of this term is confusing,and therefore, this aid as well as all others not used asspectacles will be called telescopic hand magnifiers.

17 The historical survey up to 1910 was abstracted fromthe set of articles entitled "Zur Entwicklung der Fernrohr-brille" by M. von Rohr. Cf. Bibliography.

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fying lens. He seems to have been interested,primarily, in the theoretical possibilities. Heextended the theory of the two-lens telescope toafocal magnifying lenses by assuming the in-terspace between the lens elements to be filledwith water. He then considered replacing thewater with glass, and also proposed making thewhole unit out of a single piece of glass in theform of a cone.

The first unit actually constructed on theCartesian principle appears to have been madeby J. Gregory in 1663. He wanted "to make froma single lens, a telescope which would magnifythe retinal image of a distant object, and thusenable presbyopes to perceive the object dis-tinctly." The success he attained in correctingthe refractive error and combining with it atelescopic component cannot be determined.

In 1785, J. Stock suggested the use of afocalmagnifying lenses to be worn as glasses in frontof the eyes. Unfortunately, very incomplete in-formation was available from the reference.

A distinct cleavage in the development ofthese devices was brought about by the en-deavors of G. Schbnstedt, whose description waspublished about 1835. He suggested making theunit from a thick double convex lens with onlyone surface polished. A concavity of smallerdiameter than that of the anterior surface wasthen to be ground into the unpolished rear sur-face. The power of such a unit could be varieddepending on the curvatures of the two surfaces.Schonstedt recommended that myopes couldadvantageously use such glasses with the properrefractive correction in place of lorgnettes.

Units with a higher magnification and a neces-sarily greater separation of the two surfaces ofthe lens were available by 1866. Donders con-sidered them as one of the aids to be used for thereduced acuity of high myopia at distant vision.He mentions the fact that the concave surfacecan be varied in curvature so as to correct therefractive error of the myope. One of the highmagnification units available at that time wasmanufactured by A. Steinheil in Munich. Theseunits were used only monocularly and probablyalways as a hand lens because of their weight.

A complete theoretical investigation of theeffect of changes of curvatures of the surfacesand thicknesses of the lenses was made by K.

Stellwag von Carion, and a report of his studieswas published in 1870. In it this scientist gavethe formulas for principal and focal point dis-tances as well as the magnification of such ar-rangements. An actual set of magnification lenseshaving various refractive powers was producedfor the Viennese World's Fair in 1872 at theinstigation of Professor Stellwag. The lenseswere so constructed that they could easily beworn in spectacle frames without undue dis-comfort due to weight. The curvature of the frontsurface was varied to produce different refractivepowers. For the lenses which had no power butonly magnification, the thickness was 6.6 mmand the radius of curvature of the front surfacewas 19.7 mm. This produced a basic magnifica-tion of 1.5 X or 50 percent.

Afocal and terrascopic' 5 as well as refractivelenses of low magnification were developed bythe Dartmouth Eye Institute in the late nine-teen twenties. 9 A theoretical investigation of theeffect of change of curvature and thickness forboth distant and near vision was made by Ogleand published in 1936. Unlike the earlier formsof magnifying lenses from which a large mag-nification was sought to aid a reduced acuity,these were designed so that anomalous inequali-ties in magnification and shape of the images ofthe two eyes, relative to each other, could becorrected.2 0 The maximum magnifications of thelenses that have been constructed are 10 percentor 1.10X.

Afocal contact lenses were patented by W.Feinbloom in 1940. One of the claims of thepatent is that various magnifications can beproduced by alteration of the curvatures andthicknesses of the corneal section without pro-ducing appreciable refractive power. The pat-entee was particularly interested in the applica-tions of his invention to the problem of sub-normal vision. A theoretical analysis of the mag-

18 Lenses designed for a near visual distance so thatimage and object are coincident though of different size.

19 These lenses are called iseikonic. A literal translationfrom its Greek derivatives is "equal size."

20 This binocular anomaly is called aniseikonia. It hasbeen found that the presence of aniseikonia gives rise tosymptoms similar to those resulting from a muscle im-balance or uncorrected refractive errors.

Individuals with subnormal vision only rarely have theproblem of fusing images of the two eyes, because one ofthe two images is usually so poorly defined that it ispsychically suppressed.

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z zIni -n.

FIG. 7. Univis afocal magnifying unit adjusted for distantvision and mounted in a carrier lens.

nifying properties of refractive and afocal con-tact lenses was made by Boeder and publishedin 1938. Although this author considered onlythe correction of aniseikonia with contact lenses,his results are directly applicable to the problemof subnormal vision.

The most important application of the afocalmagnifying unit to be used as a spectacle to aidsubnormal vision was made by the Univis LensCompany, Dayton, Ohio.2 ' The unit is con-structed from three glass elements having dif-ferent indices and v values in order to correctthe aberrations of the system. The three glasselements are fused, and the composite unit issimilar in appearance to the design originallysuggested by Descartes, although considerablysmaller. Two magnifications 1.5 X and 2.OX,are provided.

The magnifying unit is countersunk in thecenter of a carrier lens for distant vision andslightly below the center for reading2 2 (Fig. 7).Refractive corrections are incorporated either bychanging the curvature of the front surface ofthe objective or by cementing a corrective lensto the rear surface of the eyepiece. If one desiresto use the same magnifying unit for distance andnear, small convex lenses in plastic mounts areslipped over the objective end of the magnifyingsystem.

21 A telescopic trial set manufactured by this company isavailable at the present time. It consists of both 1.5X and2.OX telescopic units as well as reading additions ofvarious powers.

22 The carrier lens can be ground so as to correct therefractive error of the user. The Zeiss Company was thefirst to suggest this unique mount for a telescopic unit.The first reference to it encountered in the literature wasby J. Nordenson in 1924 (cf. Bibliography).

B. Other Devices

The telescopic systems ae not the only oneswhich can be employed to produce magnifica-tion. Other devices, such as reading lenses andprojection systems are also available. Mechanicaldevices such as pinhole spectacles or stenopaicslits are often of considerable assistance in in-creasing the visual acuity of an eye with ananomalous refractive condition. Contact lenseshave proved to be of value in cases of irregularrefraction caused by anomalies of the cornea.These devices can be conveniently classified to-gether because their development has not beenmotivated by a desire to specifically aid in-dividuals with subnormal vision. For this reason,the historical development of the devices willnot be discussed, and attention will be centeredonly on the devices which are now available.

1. Reading Lenses

A large number of reading lenses are availableat the present time.2 3 These vary from thesimple plano-convex lens, which can be found inalmost any variety store, to the highly correctedmagnifiers having excellent field properties. Sincemany companies are usually engaged in themanufacture of the same type of lens, it is need-less to discuss the products of each. Rather, 'anattempt will be made to discuss the differenceswhich are found among the various types of lenses.

Double and plano-convex reading lenses ofvarying sizes and powers are readily available.2 4

As a rule, the larger the diameter of the lens, thesmaller its power. This rule is generally followedbecause of the undesirable weight of large lenses,as well as the excessive aberrations encounteredwhen both size and power are increased. In orderto reduce weight and yet maintain full fieldwidth, the lenses are often cut rectangular inshape.25 These lenses are mounted in wide rims

91 Unless specific mention is otherwise made, it should beassumed that the lenses are made of glass.

24 For example, the Bausch and Lomb Optical Companymanufactures round, double convex, reading lenses from2k" to 5" in diameter. The 2" lens has a power of 6.66diopters and the 5" reading lens 3.33 diopters. Approxi-mately the same types are manufactured by the AmericanOptical Company.

25 The largest rectangular shaped lens used as an aid forreading which has been found recorded in the literaturewas 6.5 i. long and 3.25 in. wide (Stockwell, cf. Bibliog-raphy). It was used in a sight conservation class in Leeds,England. The power of the lens was +3.5 diopters and it

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in order to protect the surfaces of the lenses; ahandle is usually attached to the rim. The poordefinition at the edges of the fields is a commonlyknown shortcoming.

Semi-achromatic reading lenses, composed oftwo slightly separated plano-convex lenses, withthe convex sides facing, are available. This de-sign provides a greater correction for sphericaland chromatic aberrations than can be obtainedwith a single lens, and its large field is relativelyfree from distortion.2 6

When an attempt is made to increase themagnification of an ordinary reading lens of afixed size by increasing the refractive power ofthe lens, excessive aberrations are encountered inall portions of the field of the. lens except a smallarea at the center.2 7 To overcome this difficultyvarious types of corrected magnifiers have beendeveloped. Several designs necessitate the useof a number of optical elements. The tripleaplanat (Fig. 8A) consists of a double convexlens of crown glass surrounded by two negativemeniscus lenses of flint. The color correction isexcellent. The Coddington magnifier shown inFig. 8B has only fair correction of the field prop-erties. The doublet shown in' Fig. 8C is onlypartially corrected for lateral chromatism. Com-plete achromatism requires that the lens surfacebe in contact with the object. In actual practice,however, the object and lens surfaces are slightlyseparated. Magnifications to 20 X can be securedfrom either the doublet, Coddington, or Hastingstriplet aplanat magnifiers, but their fields arevery small.

Another form of reading lens is an almosthemispheric type, shown in Figs. 8D and E,

was plano-con- ex in shape. It was mounted in a rigidframe and attached to a desk. A cowl for a lamp was builtinto the top part of the frame and served as a reflector.

26 The Bausch and Lomb Optical Company marketsonly one size of this type of lens. It is 3" in diameter andhas a refractive power of 5.71 diopters. The KollmorgenOptical Company manufactures units of this design havingpowers of 8X and 16X and markets them under the tradename of "Microvisor." The lenses are mounted in a trans-parent plastic housing 36 mm in diameter. A flange onone edge of the housing permits the unit to be convenientlymounted in a spectacle frame.

27 The magnification of a reading (thin) lens is given by,

M= 1 / [1 -(2 p-h)],

in which f represents the focal length of the lens; h, thedistance of the lens from the eye, and p, the distance ofthe object from the eye. When f =p-h, the magnificationis M=p/f.

which rests on the object being viewed. Thedifficulty of holding a hand magnifier steady isentirely overcome by this lens. The advantage ofthis type is its light-collecting property and itsdistortion-free field.2 8

The various types of reading glasses whichhave been discussed above are composed oflenses having only spherical curvatures. How-ever, different types of curvatures have beenused similar to those on aspherical and cylin-drical lenses.

Aspherical lenses have been designed prin-cipally to eliminate distortion of the field. Thisdefect is especially pronounced in lenses of highpower which must be used to secure high mag-nification. For this reason the aspherical lenseswhich are being marketed are relatively small insize.29 The manufacturing problems involved in

A B

D

.1

C

E

FIG. 8. Various types of magnifying lenses and units areillustrated above. The magnifying unit illustrated in A isknown as the Hastings' triplet aplanat and the one in Bthe Coddington aplanat. The reading lens shown in D ismade of glass, while E is composed of a transparent plasticmaterial.

28 The Carl Zeiss Company, markets two sizes of thistype of reading lens. One is 1k" in diameter and the other28". The Univis Lens Company makes available the sametype of lens as the Zeiss Company. In addition they haveintroduced another one in plastic (methyl methacrylate)which has the form illustrated in 8E. The diameter of theUnivis units on the flat surface are 1" and 1.5".

29 The Carl Zeiss Company markets three asphericalreading lenses having the following characteristics:

Lens diameter 2" 1X" lv'Magnification 3.5 X 4.0 X 8.0 X

The aspherical curve is ground on only one surface. Thelens is composed of a single glass element.

687

I

V. J. ELLERBROCK

their production are many; as a result they areexpensive.

Cylindrical reading lenses designed to producevarying magnification of the image in only onemeridian have been manufactured. The fieldcharacteristics are good for the lower powers butbecome poorer with the higher powers. The lackof definition is especially pronounced near theedges of the lens. Perhaps the most esirablefeature of this device is that it magnifies anumber of lines of printed matter equally acrossa page, and consequently one has to move itonly a few times when reading the full length ofthe page. The lenses come in various lengths upto twelve inches. The advantage of making thistype of lens from plastic material instead of glasslies in the decreased weight and cost. The onlydisadvantage, of plastic appears to be its sus-ceptibility to abrasions.

Numerous head-borne devices have been de-signed to hold reading lenses in front of the eyes.The most common of these is the ordinary spec-tacle frame. However, the amount of adjustmentthat can be made on it in varying the separationbetween the lenses and the eyes is very limited;for this reason, mounts have been designed tohold reading lenses at a relatively large distancefrom the eyes. These mounts usually rest uponthe forehead and are supported by a band aroundthe back of the head.3 0

LENS

INVERTEDOBJECT

TRANSLUCENTSCREEN

A

Ž{1 -UPRIGHTOBJECT

OPAQUE

MIRRO~ _ _ SCREEN

B

:--Z4MIRROR

MIRROR ~ CTRANSLUCENT

-y I SCREEN

MIRROR --- /MIRRORD

FIG. 9. Schematic illustrations of various projectionsystems which can be used to aid subnormal vision. Thearrangements shown in C and D are especially noteworthybecause the material to be magnified and the focusingscreen are juxtaposed.

The magnification that can be produced byany head-borne device is definitely limited. Forlow magnifications, lenses with long focal lengthsare employed. In order that the accommodationof the eyes may not be unduly taxed while usingthe device, the object viewed must be placed infront of the lens at a distance slightly less thanthe focal length. The actual working distance,i.e., the distance from the object viewed to the

TABLE II. Tabulation of pertinent data on 525 cases of subnormal vision.**

Wolff

Telescopicspectacle

41

Raefler

Telescopicspectacleand handmagnifier

148

31

20/1000to 20/35

20/500to 20/40

Gradle and Stein

Telescopics pectacle

1

45

20/200to 20/60

Mayer

Telescopicspectacle

45

63

20/300to 20/50

Brunner

Telescopicspectacle

19

39

20/300to 20/40

Investigator

Magnifyingdevice

Number ofcases aided

Mean of agedistribution(years)*

Range of bestvisual acuitywith ordinarylens correction

Feinbloom

TelescopicspectacleReading lensContact lensPinholespectacle

298

60

* Age of patients ranged between 8-87 years.** This table was partially tabulated by Feinbloom.

30 An example is Ohe one marketed under te trade name, "magni focuser." It consists of two +5.00 diopter lensesfixed in a plastic mount with their optical centers having a 38.0-mm separation. When properly worn, the lenses areapproximately 50 mm from the eyes.

20/1000to 20/80

688


eye is thus the sum of the distances of the lensfrom the eye and of the object from the lens.When a high magnification is desired, a lens ofgreater power (shorter focal length) must beused, and thus the working distance is consider-ably reduced. This necessitates that either thehead be moved toward the reading matter or thereading matter be brought closer to the lenses.Either alternative is inconvenient. Another fac-tor limiting the magnification of a head-bornedevice is that an'increase in the magnificationcauses a decrease of the depth of focus. Conse-quently, the freedom of head movements whilemaintaining clear, comfortable vision varies in-versely with the magnification. A third factorwhich limits the magnification of a head-bornereading lens as well as any type of reading deviceis the comfortable limits of eye movements.With high magnifications, head movements mustbe coordinated with eye movements to limit theextent of the latter in the eye sockets. Withouthead movements, the limit of the magnificationfor reading material at 25 to 30 inches is 2.5 Xto 3.OX.

A hand lens, or one mounted on a stand, usu-ally requires a movement of the lens across thefield to cover the object. This has proved to betedious and tiresome. To overcome this dif-ficulty, various instruments have been developedto move the lens in front of the reading matteror to move the reading matter behind the lens.The latter is well illustrated by the instrumentshown in Fig. 6A. A simple example of an in-strument to move the lens at a fixed distance infront of the reading matter was the one designedand built by C. Kappes. The reading lens wasmounted on two racks which permitted the lensto be moved from side to side, and up and down.3

2. Contact Lenses

The role of contact lenses in the alleviation ofsubnormal vision hardly needs to be discussed,A contact lens has been suggested many timesas the only practical aid for subnormal visionwhich results from irregular or scarr'ed conditionsof the cornea, such as irregular astigmatism andconical cornea (keratoconus).

31 This device is not commercially produced. A schematicdrawing of it can be found in the report of the surveysubmitted to the Committee on Sensory Aids.

Contact lenses are made of both glass andtransparent plastic.32 The refractive error of theeye can be corrected by changing the curvatureof the anterior surface of the ocular portion ofthe lens.

The use of a contact lens as a telescopic eye-piece has already been discussed.

3. Pinhole Spectacles-Stenopaic Slits

The usual design of these mechanical aids callsfor either numerous small holes or a single nar-row slit to be punched out of a thin, blackened,opaque sheet. The latter, in turn, is cut to suchsize and shape that it can be fitted in an ordinaryspectacle frame.

An unusual design of a pinhole spectacle wassuggested by H. Flaschentrager (cf. Bibliog-raphy), in which an iris diaphram provided avariable aperture. For general wear on the street,a large aperture and thus a wide field could beused, and when need for sharp vision arose, thesize of the opening could immediately be reduced.

Both pinhole spectacles and stenopaic slitsare principally used to aid subnormal vision re-sulting from irregular refractive errors. In somecases they have proven more satisfactory thaneither contact lenses or telescopic units. Themain objections to their use are the reducedbrightness and the diminished size of the visualfield. Also, when the size of the openings is ofthe order of 0.75 mm or less, troublesome dif-fraction effects are usually encountered.

4. Tubular Spectacles-Shields

Several investigators have stated the necessityof shielding the eye from extraneous light whensubnormal vision results from opacities of thecrystalline lens and cornea. Paton accomplishedthis by the use of small tubes mounted in spec-tacle frames.33 He cited two cases where sub-normal vision was produced by cataracts andwhich were considerably aided by the use oftubular spectacles for reading. Without the de-vice, one was able to read only Jaeger test type8; with it, Jaeger 2 could be read. The second

32 In the last few years there has been an increase in theuse of contact lenses; they are being manufactured by anumber of American and European firms.

33 Unfortunately, no information can be found concerningthe dimensions of the tubes used.

689

V. J. ELLERBROCK

Z3Q-- -- -U DI, ,,30 -

10 ~ 20 - -- - 9 T LESCO IC/1 AID

I10

1.0 0.1 0s.oDECIMAL VISUAL ACUITY (LOG SCALE)

FIG. 10. Graphical illustration of the increase in thevisual acuity secured by the use of telescopic spectaclesand hand magnifiers. The measured acuities were fordistant vision only. The acuity of the better eye of each of148 patients was used to secure the data. Sixteen of thesepatients were tested with both telescopic spectacles andhand magnifiers making the total number of results plotted164. (Raefler-Frommannsche Buchdruckerei.)

showed an improvement from Jaeger 12 toJaeger 1.

Another device to exclude extraneous lightfrom the field of fixation was recommended byC. F. Prentice in 1897. He suggested the use of alarge opaque shield which had a slit-aperturewhose dimensions were comparable to the lengthand width of several lines of print. The shieldwas laid over the material being read. The devicehas been found to be especially serviceable tocataract patients and amblyopes wearing highcorrections.3 4 Streiff suggested the use of an eyeshade to shield extraneous light from the fieldof view.

5. Projection Systems

Projectors have only occasionally been usedto aid persons with subnormal vision. For themost part these were individually designed andcustom built, since none have been commerciallymanufactured. On the other hand, the standardprojectors can be easily altered so as to be con-veniently used by an individual with subnormalvision. Schematic diagrams of the projectors de-signed by Dr. Jehle of Harvard University areillustrated in Fig. 9 (C and D). Of the four de-signs shown, C and D are noteworthy becausethe focusing screen and the object being magni-

3 Tle A Iericani Ecyclopedia of Ophthalmology, Vol.XVII, p. 13,473.

fied are close to each other. This enables easymanipulation of the object while its image isbeing viewed on the screen.A5

The advantage of a projection system is thatmagnifications from 5 to 20 X can be easilyprovided. The disadvantages are: the high cost,the necessity of using it in a darkened room, the"jump" of the image on the screen when thereading matter is moved, and the fact that theinstrument is not easily portable because of itsweight and size.

III. CLINICAL EVALUATION OF THE AIDSFOR SUBNORMAL VISION

There are six significant reports in the litera-ture on the clinical results secured by the useof telescopic aids for subnormal vision." Five ofthe six are case reports describing the use of the1.3X and 1.8X Zeiss telescopic spectacles. Inaddition, one of the five reports includes theuse of the 3 X, 6 X, and 8 X Zeiss telescopichand magnifiers. The sixth report describes theresults of the study of 500 cases of subnormalvision and statistically depicts the success ob-tained. Seven different types of visual aids wereused in the study. Among them were three typesof telescopic spectacles having powers of 2.2 X,1.8X, 1.5X and a fourth having a power of1.8X in the horizontal meridian and 1.3X inthe vertical meridian.

Five hundred and twenty-five cases of sub-normal vision were considered in the six reports.The range of acuities for which an aid was usedas well as other pertinent information is givenin Table II.

The increase in visual acuity secured byRaefler through the use of telescopic spectaclesand hand magnifiers is illustrated in Fig. 10.

TABLE III.

Group

A (aided)B (aided, but not practical)C (not aided)

No. ofcases

29810597

% on basisof 500

59.5%21.1%19.4%

35 Instruments constructed on the optical principlesillustrated in Fig. 40, A and B, are commercially pro-duced and known under various trade names such asEpidiascope, Balopticon, and Delineascope.

36 H. Wolff (1918), Johannes Raefler (1919), H. Gradleani J. Stein (1924), L. Mayer (1927), A. Brunner (1930),and W. Feinbloom (1934).

690


The total number of patients used to obtainthese data is 148. Sixteen patients were suppliedwith both telescopic spectacles and hand mag-nifiers making a total of 164 whose results couldbe plotted. It should be noted that the distantvisual acuity of approximately two-thirds of allthe patients has been increased to 20/60 orbetter. The number of those who would have anacuity of that value for near would be expected tobe appreciably higher.3 7

The only report of any large number of indi-viduals with subnormal vision who have beenaided by contact lenses and pinhole spectacles isthat of Feinbloom. The latter was able to giveat least 20/50 vision to thirty-four patients whohad 20/80 vision in the eye with the best visualacuity. Twenty-two of the thirty-four were aidedby pinhole spectacles and the remaining twelveby contact lenses.

There is considerable difference of opinion bythose who prescribe subnormal visual aids as tothe percentage of patients that can be given satis-factory aid. In an attempt to answer this con-fusing problem, Feinbloom made a statisticalstudy of the results of 500 unselected cases ofsubnormal vision. He was able to divide theminto the three groups given in Table III, ac-cording to the extent to which they were aidedby the device.

A further analysis of Group A is given in Table'V.

38

These statistics are of interest since roughly60 percent of the patients whose visual acuitiesranged from 20/80 to 20/1000 had been satis-factorily aided.3 9 Three-fourths of this percent-age have utilized telescopic spectacles in one

37 This is true since the reading add which must be usedfor near with a telescopic spectacle or hand magnifierproduces a magnification.

38 It should be pointed out that there is some question asto the reliability of these results. The percentage of patients(46 percent), who, Feinbloom claims, can be satisfactorilyaided by the use of telescopic spectacles is very high.According to the opinions of the ophthalmologists andoptometrists 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 1percent or 2 percent.

39 Obviously, any controversy about the percentage ofpatients aided might be a result of the lack of understand-ing of the term "satisfactorily aided." As it is used here, itmeans at least 20/50 vision for near. Likewise, the termimplies that vision with the aided eye can be achievedwithout undue',discomfort and annoyance from the me-chanical or optical device employed.

TABLE IV.

Numberof cases % of total Device used

104 35% 2.2X spherical telescopic spectacle46 15% 1.8 X spherical telescopic spectacle16 5% 1.5 X spherical telescopic spectacle63 21% 1.8 X by 1.3 X cylindrical telescopic

spectacle35 12 % Microscopic spectacle (microvisor)22 7% Pinhole spectacle12 4% Contact lenses

form or another. Feinbloom, who has made amore thorough study of this problem than anyother investigator, claims that his success wasattributed principally to the consideration of thepsychological problems associated with thesecases of subnormal vision.

Other investigators who have made studies ofthe correction of' subnormal vision are in generalagreement that patients find considerable dif-ficulty in their first attempts to use telescopicspectacles.4 0 Gradle and Stein contend that thepatient must persist in his efforts to use thedevices for a long period of time, and only thenwill he be able to make efficient use of his in-crease in visual acuity without undue discomfort.Feinbloom is not only of the same opinion aboutthe time necessary for adjustment, but likewiseinsists that many patients definitely resist un-dertaking or carrying out this training process.He reports that ". . . this resistance is not due tothe limitations of the device as was previouslythought, but to the presence of psychological prob-lems superimposed on the visual ones." If, as hemaintains, so many patients definitely resist ad-justing themselves to telescopic spectacles, andif this task of adjustment is left to the patienthimself, there is little wonder for the prevailingopinion that the use of devices for the aid of sub-normal vision is limited.

The psychological factors which cause thepatient to resist the necessary adaptation appearto be principally personality disorders. For ex-

4 0An interesting comment by Leo Mayer (cf. Bibliog-raphy) in this.regard is "I shall not try to explain themethods of fitting telescopic spectacles; suffice it to saythat only with many trials, constant urging, and an un-limited amount of patience is one able even to attempt thismode of increasing sight." In another report he stated that". . . no amount of case reports or explanation could inany measure bring to you the knowledge of the amount ofpatience, care and even coercion necessary to urge thepatient to wear telescopic spectacles."

691

V. J. ELLERBROCK

ample, some patients are deeply disturbed overthe possibility of imminent blindness, eventhough the pathology has been satisfactorilytreated. Therefore, when unaided normal visioncannot be fully restored, it often becomes impos-sible for them to be concerned with anything thatimproves their vision.

On the other hand, some patients develop suchcomplacency and so' satisfactorily adapt them-selves that they resist any attempt at change intheir vision. Those trained as blind people usu-ally do not seek further aid, nor do they readilyaccept any visual aid when it is offered.

The fact that almost 60 percent of the patientswith subnormal vision could be given satis-factory aid by an investigator who understoodthe psychological factors as compared to thepercentage aided when those factors were nottaken into account indicates their importance inthe problem of aids for subnormal vision.

IV. POLICIES AND RECOMMENDATIONS OF PRO-FESSIONAL GROUPS AND GOVERNMENT

UNITS REGARDING THE AIDS FORSUBNORMAL VISION41

A. Opinion and Recommendation of Ophthal-mologists and Optometrists

It has been impossible to secure a generalconcensus of opinion or reports of thoroughclinical evaluations of each of the available de-vices. Only the important objections raised byophthalmologists and optometrists can be pointedout.

The most frequent objection to telescopicspectacles and hand magnifiers is the limitedfield of vision. For example, with the Zeiss 1.3 Xtelescopic spectacle the field is only about 40degrees for distant vision; at near, it is stillfurther reduced. The visual field and the freeworking distance, moreover, decreases with theincrease in magnification.4 2 An objection to thehead-borne devices is the confusion and discom-fort arising from the apparent movement ofstationary objects when the head is turned. In

41 Any survey of this nature necessarily entails a greatobligation to the individuals and organizations who gaveinformation, expressed opinions, and made recommenda-tions. The author wishes to acknowledge the assistance heobtained.

42 The free-vorking disLanice is defiled as the distancefrom the object surface to the front surface of the telescopicunit.

some instances, the patient has a feeling ofnausea. Also, patients usually object to theweight of the units which must be worn as spec-tacles because of the pressure on the nasal bonefrom the pad supports. The high cost is stillanother objection frequently reported in the useof these units. Since the improvement of thevision expected is often not secured until sometime after the units have been worn, the patientmay be unwilling to buy an expensive device.43

In spite of these objections, the ophthalmolo-gists and optometrists who have used telescopicspectacles and hand magnifiers regard them as animportant aid -to some patients. The low per-centage of those patients who obtained satis-factory help from the use of the devices is prin-cipally attributed to the objectionable featuresof the various aids.4 4

B. Policy of the Medical Corps of the Armed.Forces of the United States and

Veterans Administration

The policies of the various branches of theArmed Forces and the Veterans Administrationmust be considered together with regard to aidprovided for the war-blinded and those incurring.subnormal vision. In effect, the Medical Corpsof the Armed Forces and the Veterans Adminis-tration attempt to meliorate all gradations ofreduced acuity including the totally blind.

Rehabilitation is carried on not only while thewounded or injured member is in the service butalso after his discharge. The in-service rehabilita-tion is commenced as soon as the individual isphysically fit. The policy of all medical branchesin regard to subnormal vision is to provide anyaid recognized by the medical profession, thechoice being at the discretion of the attendingophthalmologist.4 5 When a member of the Armed

4 The ophthalmologist Mayer will not give out-of-townpatients subnormal vision aids for trial, but requiresthem to buy it outright if it improves their vision to hissatisfaction and providing, of course, that the patientsare able to afford the cost. He has found that if a personhas invested in an aid, there is a greater likelihood that hewill attempt to use it. [Arch. Ophth. 2, 316 (1929).]

44 It is unfortunate that so few ophthalmologists andoptometrists have had training in the use of telescopicspectacles. Without doubt this fact partially accounts forthe failure of the eye professions to prescribe them.

4S Little or no information is at hand as to whether or nottelescopic trial sets are available at the various eye centers.To what extent individuals who are in need of the aids aretested and equipped with them is also not known. How-

692


Forces is discharged, his case is transferred tothe Veterans Administration. If an aid is thenrecommended by the attending ophthalmologist,but has not as yet been provided, the VeteransAdministration supplies him with it.

An important point in regard to policy is thatthe war blinded soldier or veteran (with a visualacuity of less than 20/200) has to be providedwith a prescribed course of social rehabilitationand training in the manual arts and the readingof Braille.4 6 If an individual has slightly betterthan 20/200 acuity, no optical aid or training inits use must needs be provided. Whether or notit is furnished depends entirely on the discretionof the ophthalmologist, who may or may not beacquainted with the available aids and who mayor may not know when and how to carry out theexamination and the prescription. If an indi-vidual is fortunate enough to have an aid pro-vided for him, the probability exists that he willbe given very little or not assistance in learninghow to use and become adapted to the device.

C. Opinion and Recommendation of SightConservation Program Personnel

The National Society for the Prevention ofBlindness promotes sight conservation classes ingrade and high schools and in the schools for theblind throughout the country. To date, there areabout 630 of these classes in the United States.The purpose of establishing such classes was "toprovide educational opportunities for childrenwith such low visual acuity that they cannotprofitably use the ordinary school equipment.This group includes those having a visual acuitybetween 20/70 and 20/200 in the better eye,with the best correction of the refractive errorobtainable with ordinary ophthalmic lenses. '47

This group has been labeled the "pedagogicalblind."4 8

The important advantage of these classes is,

ever, there is reason to suspect that such sets are onlyfortuitously available at a few scattered places.

46 This policy is the result of the recommendations of thein-service Rehabilitation Committee set up by PresidentRoosevelt during World War II

" C. Berens and W. Hathaway, "Sight saving classes,"Arch. Opth. 18, 845-849 (1935).

48 For the definitions of total, economic, vocational, andeducational blindness, see E. Jackson, A. C. Snell, andH. S. Gradle, "Report of the Committee on Definition ofBlindness," J.A.M.A., 1032, 1445-1446 (1934).

"that educational media is provided which thechild is able to see without undue effort; booksin large clear type; pencils, chalk, paper, etc.,that will enable clear writing. . . .".7 Thus, theattempt is made to alter the object matter, suchas books, etc., so that it can be perceived byan individual having subnormal vision.

The cost of printing an edition of a standardtext in large type print, however, is high; as aconsequence, only the more generally used bookssuch as those employed in the lower grades areavailable. Facing this limitation, some sight-conservation class teachers have attempted touse those reading lenses which are available inorder to aid students with subnormal vision intheir reading of textbooks printed in standardsizes of type. Unfortunately the reading lenseswhich can be purchased at the present time arenot very satisfactory for such use. The teachersdesire a large, well-corrected, reasonably pricedreading lens. Such a lens produced in largeenough quantities would be a real advance inthe educational program for all children afflictedwith subnormal vision.

The possibility exists that the design of thelens would necessitate its being moved across apage in order for an individual to read a line ofprint. Should this be the case, a mechanical de-vice would have to be provided to facilitate themoving of the lens while reading. Even if thelens were large enough to magnify an entireline of print without a horizontal movement, avertical movement would still be necessary toread an entire page.

V. CONCLUSIONS

The foremost conclusion which can be drawnfrom this survey is that the problem of opticalaids for subnormal vision involves many morefactors than has been generally suspected. Prin-cipal among these are the personality disorders ofthe patients who attempt to use the aids. Itappears that a lack of consideration of thisfactor can produce very poor clinical resultswhich usually have been mistakenly attributedto an inadequacy or an objectionable feature ofthe optical mechanical device employed. Theconfused notions as to their clinical efficacy indi-cates the desirability for a thorough investiga-tion of all psychological factors encountered in

693

V. J. ELLERBROCK

the fitting and use of an aid. Such an investiga-tion of this nature should study the role of thepersonality disorders of the patients, the causesfor the period of adjustment required before apatient with subnormal vision can use an aid,and the perceptual and reading problemsinvolved.

The answers to some of these problems arepartially known. For example, the period ofadjustment is necessary because "the individualhas to alter the normal relationship between eyeand head movement when reading with a devicebefore the eyes. The patient must also learn tomove the paper or book rather than his head;reduce his reading span to single words or evenletters at a time; compensate for lack of depth offocus by keeping the reading material at a fixedplane; learn to use sufficient and proper illumina-tion, etc." (Feinbloom).

The role of the visual factor, in view of thepersonality of the individual with certain eyedefects, was extensively studied at the Dart-mouth Eye Institute. One of the findings of thisinvestigation was "that, in the particular groupstudied, the motivational pattern of the indi-vidual is the principal factor that determinesthe nature of the individual's adjustment to his,visual defects or their correction. Each indi-vidual responded to his visual difficulty in a wayconsistent with his prevailing mode of adjust-ment. The visual condition could not be con-sidered apart from the motivational structure.""

Such findings could serve as a basis from whichto commence a more thorough investigation ofthe role of all the psychological factors.

Although there is a need for improvement inthe design of telescopic units resulting in a re-duction of weight and increase of size of field, thepossibility that any improvement would beclinically' significant is very small. The telescopicunits which are available at the present time, orat least, which have been proposed, obviatepractically every objection which has been madeto this conventional aid. It remains for the eyeprofessions to exploit and apply the various typesand to subject them to a thorough clinicalevaluation.

Possible improvement of aids for subnormal

49 Bender, Imus, et al., Dartmouth College Publications(1942), pp. 323-32.

vision which are not head-borne appears highlydesirable. Although many different types ofreading lenses of various size, shape and powerare available, a new design specifically for theaid of subnormal vision might be developed,taking advantage of new manufacturing methods.Such a lens would have to be no less than sixinches in diameter and relatively well corrected.A magnification of 3.0X or 200 percent would benecessary if individuals whose acuity was notless than 20/200 nor better than 20/70 could beaided. A reading lens of this type would probablyhave to be used monocularly.

For subnormal vision from 20/200 to 20/1500the development of projection devices mightbe considered. 0 The optical system of such adevice could take a form similar to one of thedevices developed by Jehle. However, a systemwhich has hitherto not been developed and whichmay offer even greater possibilities is a projectorbased on the design of the Schmidt astronomicalcamera. A modification of this design has beenand is now being successfully used in televisionprojection. Such a system might provide rela-tively high magnifications with adequate il-lumination and contrast to an extent which hashitherto been impossible. The projector would bedesigned to produce magnifications of opaqueobjects such as books or other printed matter.The magnified image would be formed on atranslucent screen which would necessitate theprojector being used in a semi-dark room. Sincelarge magnifications would have to be providedon a relatively small screen, a device would benecessary to allow the printed material to beeasily moved and the successive parts magnified.

BIBLIOGRAPHY

M. L. Berliner, "A new type of telescopic lens," Arch.Ophth. 16, No. 4, 649-654 (1936).

J. W. Bettman and G. S. McNair, "A contact-lens-tele-scopic system," Am. J. Ophth. 22, No. 1, 27-32 (1939).

Birch-Hirschfeld, "Ueber Fernrohrbrillen und Fernrohr-lupen fr schwachsichtige Kiegsverletzte," Zeits. f.Kriegsbeschadigten Firsorge in Ostpreussen 1, 168-170(1916).

P. Boeder, "Power and magnification properties of con-tact lenses," Arch. Ophth. 19, 54-67 (1938).

0 The Zeiss telescopic hand magnifiers and the Koll-morgen Microvisors produce magnifications to 10X.However, the very small visual field makes them practicallyuseless for reading.

694


A. B. Brunner, "Telescopic lenses as an aid to poor vision,"Am. J. Optom. 13, No. 8, 667-674 (1930).

J. Dallos, "Contact glasses, the 'Invisible' Spectacles,"Arch. Ophth. 15, 617-623 (1936).

A. F. Dittmer, Corrective Lens System, U. S. Patent No. 2,164, 801, Issued July 4, 1939. Application filed October22, 1936.

H. Eggers, "An inexpensive telescopic spectacle," Arch.Ophth. 10 (O.S. Vol. 67) No. 4, 515-517 (1933).

H. Erggelet, "ber Sampsons graphische Ableitung derAbbildungskonstanten und ihre Anwendung auf dieFernrohrbrille," Arch. f. Ophth. 86, 78-92 (1913).

-"Ein neuer Fernrohrlupenfuss," (28. IX), Zeits. f.ophth. Optik. 4, 149-153 (1916).

"Bemerkungen zur Fernrohrbrille," Zeits. f. ophth.Optik. 8, 146-154 (1920).

W. Feinbloom, "Report of 500 Cases of Subnormal Vision,"Trans. Am. Acad. Optom. 8, 58-70 (1934).

"A teloptic-magnifier aid for incomplete optic nerveatrophy," Am. J. Opt. and Arch. Am. Acad. Optom.18, No. 12, 550-558 (1941).

-- The Telescopic Spectacle and the New SubnormalVision Lens, first edition, Minneapolis, Minnesota, Am.J. Optom. (1933).

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Documents

Report on Survey of Optical Aids for Subnormal Vision