acuity li% $e. - bmj

British Journal of Ophthalmology 1995; 79: 814-820

Low vision in east African blind school students:need for optical low vision services

Janet Silver, Clare E Gilbert, Peter Spoerer, Allen Foster

Departnent ofPreventiveOphthalmology,Institute ofOphthalmnology,LondonC E GilbertA Foster

ChristoffelBlindenmission, EastAfrica Regional Office,PO Box 58004,Nairobi, KenyaP Spoerer

Visual AssessmentDepartment,Moorfields EyeHospital, LondonJ Silver

Correspondence to:Janet Silver, VisualAssessment Department,Moorfields Eye Hospital,City Road, London EC1V2PD.

Accepted for publication17 May 1995

AbstractAims-There is increasing awareness ofthe needs of children with low vision, par-ticularly in developing countries whereprogrammes of integrated education arebeing developed. However, appropriatelow vision services are usually notavailable or affordable. The aims of thisstudy were, firstly, to assess the need forspectacles and optical low vision devicesin students with low vision in schools forthe blind in Kenya and Uganda; secondly,to evaluate inexpensive locally producedlow vision devices; and, finally, to evaluatesimple methods of identifying those lowvision students who could read N5 to N8print after low vision assessment.Methods-A total of 230 students wereexamined (51 school and 16 universitystudents in Uganda and 163 students inKenya, aged 5-22 years), 147 ofwhom hada visual acuity of less than 6/18 to percep-tion of light in the better eye at presenta-tion. After refraction seven of the 147achieved 6/18 or better. Eighty two(58.6%) ofthe 140 students with low vision(corrected visual acuity in the better eyeof less than 6/18 to light perception) hadrefractive errors of more than 2 dioptresin the better eye, and 38 (271%) had morethan 2 dioptres ofastigmatism.Results-Forty six per cent of studentswith low vision (n=64) could read N5-N8print unaided or with spectacles, as coulda further 33% (n=46) with low visiondevices. Low vision devices were indicatedin a total of 50 students (3570/o). Thelocally manufactured devices could meettwo thirds of the need.$e.

Figure 1 Low vision aids produced in the optical workshop in Nairobi.

Conclusion-A corrected distance acuityof 1/60 or better had a sensitivity of 99 lI%and a specificity of 56-7% in predicting theability to discern N8 print or better. Theability to perform at least two of thethree simple tests of functional vision hada sensitivity of 95-50/o and a specificity of63.3% in identifying the students able todiscern N8 or better.(BrJ Ophthalmol 1995; 79: 814-820)

In many developing countries children withvisual disability are taught in residentialschools. This is particularly true in Africa,where programmes of integrated education arestill being developed. A significant proportionof students in schools for the blind in Africa areseverely visually impaired rather than blind,but despite this most formal education is con-ducted using techniques appropriate for thetotally blind such as braille. There is, however,increasing awareness of the needs of childrenwith low vision and some countries are nowdeveloping educational services for studentswith low vision.1 2 Being able to read ink printallows a child much greater access to informa-tion and a wider range of recreational activitiesand educational and employment opportuni-ties. For children with low vision opticaldevices may be required to attain a near acuitywhich allows access to ink print.

Until recently the World HealthOrganisation's (WHO) category of low visionwas a corrected acuity in the better eye of lessthan 6/60 to 3/60. However, this definition isrestrictive, as many individuals who haveacuities of less than 3/60 to light perception inthe better eye have useful vision. The followingdefinition of low vision has recently beenagreed by WHO:

'A person with low vision is one who hasimpairment of visual function even aftertreatment and/or refractive correction, andhas a visual acuity in the better eye of lessthan 6/18 to light perception, or a visual fieldof less than 100 from the point of fixation,but who uses or is potentially able to usevision for the planning or execution of atask.'lChristoffel Blindenmission (CBM) a non-

governmental development organisationinvolved in prevention of blindness pro-grammes throughout the developing world,also provides support for children in schoolsfor the blind. CBM promotes optical work-shops which produce low cost spectacles.3 Arange of low vision devices (LVDs) has beendeveloped at the optical workshop nearNairobi (Fig 1). The devices are robust and

814

on February 16, 2022 by guest. P

rotected by copyright.http://bjo.bm

j.com/

Br J O

phthalmol: first published as 10.1136/bjo.79.9.814 on 1 S

eptember 1995. D

ownloaded from

http://bjo.bmj.com/

Low vision in east African blind school students: needfor optical and low vision services

inexpensive, but had not been field tested, andit was not known how well the range anddesign would meet the needs of children withlow vision.The aims and objectives of the study were as

follows:(1) to determine the range of refractive

errors and need for distance spectacles in stu-dents with low vision in schools for the blind ineast Africa;

(2) to determine the proportion of studentswith low vision who have the potential todiscern N5-N8 or N10-N36 print afteraccurate refraction and assessment with LVDs;

(3) to determine from a range ofLVDs thatmeet British and international standards thetype of devices required, and the feasibility ofcreating a smaller range that would be helpfulto the majority of students who have the poten-tial to benefit;

(4) to determine to what extent the locallyproduced (CBM) LVDs could meet the need;

(5) to evaluate simple methods which couldbe used by teachers and others to identifystudents who would benefit from low visionassessment.The requirements for distance LVDs, such

as telescopes, were not assessed in this study,as these have more limited applications thanthose for near work, are more difficult tomanufacture, and are expensive to purchase.

CALCULATION OF MAGNIFICATIONMagnification, or rather how it is calculated, isa complex area as the optical system of the eyeas well as the power of the LVD being usedhave to be taken into consideration. Standardcalculations are based on the equivalent powerof the lens(es). Two formulas are commonlyused for calculating the magnification of standand hand held devices; M=f/4 (formula 1),where f=the focal length ofthe lens of the LVDin dioptres (D). This is the standard formula inthe USA, and is widely used by clinicians.However, the formula M=f/4+1 (formula 2)has been promoted by certain manufacturers,and is now generally used by them. The BritishStandards Institution calls the latter 'trademagnification' and to avoid confusion theyrecommend that all magnifiers are labelled withthe equivalent power (D).4 To further compli-cate the issue, if the lens is placed closer to theobject than its focal length then its effectivemagnification is reduced and an accommoda-tive effort (or an appropriate near add) isrequired to compensate for the divergence ofthe emergent rays. The magnification of spec-tacle magnifiers (hyperoculars) can also be cal-culated using either formula, but the morefrequently used is M=f/4, which assumes thatthe material will be placed at the far point.The reading distance and, hence, size of

the image falling on the retina will also beinfluenced by the refractive error of the user.For example, when using formula 1, a x 5labelled lens (that is, +20 D) in an uncorrectedhigh myope who normally uses -12 D, willhave a total optical system of 32 D (+ 12 D ofhis own +20 D from the hyperocular). The

working distance will be 3'3 cm (100/32) andthe magnification X 8 (using f/4). If the user isaphakic, normally needing +12 D, the samehyperocular lens will produce only x2 magni-fication and the working distance will be12-5 cm (+20 from the hyperocular -12 D tocorrect the aphakia=8 D; M=8/4= X2; work-ing distance= 100/8=12 5 cm).

In an emmetropic eye 4 D of accommoda-tion (or reading add) is required to focus printat 25 cm. If the print is moved from 25 cm to12-5 cm the angle subtended at the eye willincrease by a factor of x 2 with a correspondingincrease in image size. An emmetropic eye willneed +8 D to focus the image while an uncor-rected highly short sighted (myopic) eye of-12 D will need -4 D, and an aphakic eyemight need (+20 D). The actual retinal imagesize will be very similar for each individual.However, variations are caused by the effectsof back vertex distance (BVD) and thick lensoptics, but with lenses of 20 D or less varia-tions in image size are rarely as much as 10%.5

In this study, in order to simplify the calcu-lation of magnification required by studentsthe principles outlined above have been used,and the reciprocal of the reading distance cal-culated as a measure of magnification at theeye irrespective ofthe type of optical correctionor the power of LVD required. Young peopleare able to bring print very close, using accom-modation to provide magnification, but as thiseffort is unlikely to be sustainable LVDs maybe indicated for prolonged close work.

MEASUREMENT OF NEAR VISIONSnellen charts (or their equivalent) are con-structed so that each element of the 6 metrefigure subtends 1 minute of arc at the retina ofthe viewer, the whole character subtending5 minutes. The Faculty of Ophthalmologists''N series' of reading charts, which usesprinter's type faces, is constructed so that thereis an arithmetic relation between the differentsizes of print.6 On the basis of visual anglesubtended at the eye it is possible to correlatedistance and near measurements of visualacuity. For example, a distance acuity of 6/18is equivalent to N5 at 25 cm, as both subtendthe same visual angle.The print size used in books for students is

not standardised. For the purpose of this studynear acuity was banded into two groups; N5 toN8, which would allow access to most printedmaterials, and N10 to N36 which would allowonly limited access to ink print.

Materials, subjects, and methods

MATERIALSThe Sonksen-Silver visual acuity test (S-S) wasused during refraction and low vision assess-ments. This test, which is based on Snellenacuities and which uses multiple optotypes atevery level, allows measurement of distancevisual acuity at any distance, can be used as amatching test, and can be used to measure nearvisual acuity. The S-S test has the advantage of

815



j.com/

Br J O


eptember 1995. D

ownloaded from

http://bjo.bmj.com/

Silver, Gilbert, Spoerer, Foster

Table 1 Grouping ofstudents after assessment for nearvision

Print size read!Group discerned Optical denice required

1 N5-N8 ±Own spectacles2 N5-N8 With new corrective lenses3 N5-N8 With LVD4 N1O-N36 ±Own spectacles5 N1O-N36 With new corrective lenses6 N1O-N36 With LVD7 N48 or less With any optical device

being light, portable, and readily understand-able without the benefit of a common language.Matching can be used for individuals who donot speak English or who cannot read. Snellenacuities rather than logarithm based acuitieswere used in this study as the WHO categoriesof visual loss are based on Snellen acuities.Low vision devices (stand and hand held

magnifiers, and hyperoculars) made byCombined Optical Industries were used duringthe low vision assessment. Simple magnifiersare readily available, relatively inexpensive, donot require skilled dispensing, and have beenshown to be well accepted by children.7 TheCOIL magnifiers are made using acrylic,aspheric lenses. In the stand magnifiers thelenses are mounted in a horseshoe-shapedstand so that the emergent rays are parallel(except for the 76 D which allows a little focus-ing). The stand magnifiers used in the assess-ment provided the greatest range of availablepowers (8, 12, 20, 28, 36, 44, 56, and 76 diop-tres). Hand held magnifiers of 3, 6, 12, and 20dioptres and hyperoculars (spectacle magni-fiers with surface curvatures calculated toreduce aberrations) in powers of 12, 16, 20,24, 32, 40, and 48 dioptres were also used.The magnifiers are fully described in themanufacturer's material and the literature.8 9The optical aids produced by CBM are pro-

duced from locally available materials, and canbe made by people with little previous experi-ence or knowledge, after a short period oftraining.3 With appropriate technology it ispossible to manufacture stand and hand heldmagnifiers, aphakic spectacles, and simplegalilean telescopes. The stands are made fromplastic drainpipe and the lenses are groundfrom window glass. The lens diameter isapproximately 50 mm. In the higher powersthere is little or no divergence as the standplaces the lens close to its focal length. In thelower power magnifiers the stands are rela-tively short, and demand either accommoda-tion, a near correction, or that the magnifier islifted off the page. Because each magnifier is

Table 2 Categories of visual loss before and after refraction (corrected acuity in the bettereye) in 230 students in schools for the blind in Kenya and Uganda

Before refraction After refraction

WHO categories Visual loss N % N %

No impairment 6/6-6/18 14 6-1 21 9.1Low visionVI <6/18-6/60 34 14-8 50 21-7SVI <6/60-3/60 53 23-0 48 20-9Blind <3/60-PL 60 26-1 42 18-3

Totally blind NPL 69 30-0 69 30 0Total 230 100 230 100

VI=visual impairment; SVI=severe visual impairment.

made individually, there will be small differ-ences at the same nominal power. Locally pro-duced stand magnifiers of 8, 10, 12, 16, 20,and 28 dioptres (the highest power available)were used in this study.

SUBJECTSIn Uganda 51 pupils from two schools for theblind were examined as well as 16 universitystudents. In Kenya 163 pupils from threeschools for the blind were examined. All pupilsin the Ugandan schools were examined, butthis was not possible in Kenya as the schoolswere much larger. In order to obtain a repre-sentative sample of students, classes wereselected from all age groups and all students inthose classes were examined.

METHODSDistance visual acuities were measured in eacheye separately using a Snellen E chart, withspectacles if normally worn. Visual fields wereassessed by confrontation when indicated.Students with a visual acuity less than 6/18 tolight perception in the better eye underwentthree simple, recently developed tests of func-tional vision10 and were assessed by theoptometrist.

Tests offunctional visionThree simple tests of functional vision wereundertaken to determine whether the studenthad useful residual vision for:

(1) independent mobility (that is, ability tonavigate without assistance between twochairs, set 2 metres apart, in a well lit room)

(2) social contact (that is, ability to recog-nise someone known to them at a distance of 2metres)

(3) near vision (that is, ability to recogniseor describe the shape of three 5 mm symbols atany near distance).

Low vision assessmentDistance visual acuity measurement wasrepeated using the S-S test. Near visualacuities were measured in each eye using Nseries test types, with spectacles if these wereavailable. The S-S near chart was used for stu-dents unable to read ink print. The reading dis-tance was recorded for the better eye.Refraction was performed using standard tech-niques through an undilated pupil. The bestcorrected distance and near acuities, therefractive error and the eye to near chart dis-tance were recorded for the better eye.

All students unable to read N5 to N8 beforeor after refraction were then assessed with theLVDs from the UK, using the better eye. Thelevel of near acuity achieved, the reading dis-tance, and the type and power of the LVDwere recorded. All students who benefitedfrom the British devices were then assessedusing the CBM LVDs.

After assessment the students were groupedas shown in Table 1. The prescriptions and

816



j.com/

Br J O


eptember 1995. D

ownloaded from

http://bjo.bmj.com/


Table 3 Refractive errors in 147 students with low vision at presentation in schools for theblind in Kenya and Uganda (spherical equivalents)

6118 After refraction* <6/18 To LP after refractiont

Refractive error (D) N % N %

0-20 3 430 38 27-02-25-5-0 2 28-5 37 26-45-25-8-0 0 0 9 6-48 25-11-0 0 0 10 7-211-25 ormore 2 28-5 26 18-6Refraction not possible 0 0 20 14-4Total 7 100 140 100Significant cylinder (>2) 3 42-9 35 25-0

*No impairment after refraction. tLow vision according to the new definition after refraction.

names of students and who would benefit fromspectacles or LVDs were given to the principalsof the schools and the attending ophthalmolo-gists.

Results

CATEGORIES OF VISUAL LOSSA total of 230 students was examined. Levelsofvisual loss were recorded according toWHOcategories and are shown in Table 2. Atpresentation 14 (6 1%) students had no visualimpairment. Thirty four students had visualimpairment (<6/18-6/60) and 53 wereseverely visually impairment (<6/60-3/60).Sixty students had vision in the range of lessthan 3/60 to light perception in the better eye(blind) and 69 students had no perception oflight in both eyes (totally blind). After refrac-tion the visual acuity in the better eyeimproved by one or more categories in 46students (20%).Of the 230 students included in the study,

140 (61%) were classified as having lowvision, according to the new definition. Fortytwo (30%) of the 140 students with low visionwere blind according to WHO categories ofvisual loss. The ages of individuals with lowvision ranged from 5-22 years (mean 13-6years). Forty two were aged over 15 years atthe time of the study, but all had developedvisual loss before the age of 16 years and sohave been included. Eighty nine (64%) weremale.

REFRACTIVE ERRORS IN STUDENTS WITH LOWVISIONStudents with normal vision at presentation

Table 4 Near visual acuity after assessment in 140 students in Kenya and Uganda

Subtotal1Tint size readl

Group discerned Optical device required N % N %

1 N5-N8 ±Own spectacles 56 40-02 N5-N8 With new correction 8 5-73 N5-N8 With LVD 46 32-9

110 78-64 N10-N36 ±Own spectacles 7 5-05 N1O-N36 With new correction 2 146 N10-N36 With LVD 3 2-2

12 8-67 N48 ±Own spectacles 1 0-7

N48 With LVD 1 0-7Less than N48 With any device 16 11-4

18 12-8Total 140 100 140 100

(14) and those who could not see light ineither eye (69) were not refracted. In a further20 students refraction was not possiblebecause of very low acuity combined withdense media opacity. Findings of refractionare presented in Table 3. Eighty two of the140 students with low vision had refractiveerrors of more than 2 dioptres (58-6%) and35 had astigmatism of 2 D or more (25 0%).Corrective lenses improved the visual acuityin the better eye in 59 students; by one line in37, two lines in 17, and three or more lines infive students.

Forty six students with low vision neededspectacles and in the remaining 13 theimprovement in acuity was not sufficient towarrant spectacle correction. At presentation28 students were already wearing spectacles,but in 13 the visual acuity could be improvedwith a change in prescription.

NEAR VISUAL ACUITY AFTER LOW VISIONASSESSMENTOne hundred and ten (78&6%) students withlow vision were able to discern N5 or N8 printwith or without optical devices (Table 4). Afurther 12 students (8.6%) could discernN10-N36 print. Two students could discernN48 print and 16 were unable to discern eventhe largest print.

LOW VISION DEVICES REQUIREDFifty six students (40%) were able to read N5 toN8 print at presentation, either unaided (43) orwith their own spectacles (13). All students ableto see N8 at presentation (16) were able to readN5 after accurate refraction. Eight students(6%) were able to discern N1O-N18 print atpresentation, which improved to N5-N8 withcorrective lenses and 46 students who had nearacuities ofN 10 or less at presentation were ableto read N5-N8 with LVDs.Twelve students could read N10-N36 print

but the acuity could not be improved toN5-N8. Two of these students achievedN1O-N36 with corrective lenses and three withLVDs. Five students could not be assessedwith LVDs because they were too young, orbecause of inadequate comprehension or con-centration.Two students could discern N48 print, one

with corrective lenses and one with an LVD.Overall, 27 students (19.3%) needed newspectacles to achieve their best level of nearvision and 50 (35.7%) needed LVDs.

LEVEL OF MAGNIFICATION REQUIREDThe dioptric power required has been calcu-lated from the reciprocal of the readingdistance of the better eye (Table 5). Themean dioptric power required by studentsin groups 1, 2, 4, and 5 who did notrequire LVDs is lower than the dioptricpower required by students in groups 3 and6 who did need LVDs (range of means11-25 D-14-8 D compared with 25-8 D-63 D).

817



j.com/

Br J O


eptember 1995. D

ownloaded from

http://bjo.bmj.com/


Table 5 Level of magnification required in 140 students with low vision in blind schoolsin Kenya and Uganda

Mean RangeGroup Near VA Optical device N power (D) (D)

1 [ ±Own spectacles 56 11-4 6-202 N5-N8 With new correction 8 14-8 65-333 LVD±corrective lenses 46 25-8 6-5-564 ±Own spectacles 7 14-1 6-5-335 Ni0N18 With new correction 2 11-25 10-12-56 LVD±corrective lenses 3 63-0 50-767 N48 orless 18 - -

TYPE AND RANGE OF LOW VISION DEVICESREQUIREDOf the 50 students requiring LVDs, 21 foundstand magnifiers the easiest to use (range+20 D to +76 D), a further 19 studentsbenefited from high reading adds (range + 6 Dto +20 D), and the remaining students usedhand held magnifiers (+20 D) and hyper-oculars (range +24 D to +48 D). Ninestudents needed LVDs with powers in therange +29 D to +40 D, and a further ninerequired more than +40 D (Table 6).

LOW VISION DEVICES PRODUCED BYCHRISTOFFEL BLINDENMISSIONTwenty two of the 50 students who benefitedfrom the British LVDs were able to read thesame size print with CBM LVDs of equivalentpower (Table 7). Eleven students were able toread print of the same size but they neededCBM LVDs of higher power to achieve thesame near acuity. In six students the level ofnear acuity achieved with the CBM LVDs wasnot as good as with the British LVDs. Therange of magnification available in the CBMLVDs was not adequate for students with thelowest levels of vision where high powerdevices were needed. Overall the CBM LVDswere able to meet the need in 66% of studentswho would benefit from LVDs and in 72% ofthose students who could discern N5-N8print.

IDENTIFICATION OF STUDENTS WHO HAVE THEPOTENTIAL TO BENEFIT FROM LOW VISIONSERVICESThere was a correlation between corrected dis-tance acuity in the better eye and the level ofnear acuity achieved (Table 8). Only one of 18students (5/6%) with less than 1/60 correcteddistance acuity was able to read N5-N8,compared with 60% with 1/60-2/60, 96% with3/60-5/60, and 98% with 6/60 or better.

Table 6 Range and type ofBritish low vision devices required in 50 students with lowvision

Stand High reading Hand heldmagnifiers add magnifier Hyperocular

Power N Power N Power N Mag Power N

+20D 3 +6D 3 +20D 2 X6 +24D 2+28 D 6 +10D 7 X8 +32 D 4+36 D 4 +12 D 2 x1o +40 D 1+44D 2 +16D 5 X12 +48D 1+56D 4 +20D 2+76D 2Total 21 19 2 8

Sixteen students who were blind according toWHO categories of visual loss (that is, <3/60corrected acuity in the better eye) could readN5-N8 print with LVDs.A corrected distance visual acuity - 1/60

identified students able to read N5-N8 printafter low vision assessment with a sensitivity of99 1% and a specificity of 56 7%.The results of the functional vision tests

show that 95% of students who could discernN5-N8 print were able to perform at least twoof the three tests of functional vision comparedwith 58% students able to discern N10-N36print and 22% students able to read N48 orless (Table 9). The ability to perform two orall three tests of functional vision identifiedstudents able to read N5-N8 print after lowvision assessment with a sensitivity of 95-9%and a specificity of 63-3%.

TYPE OF EDUCATIONEighty of the 140 students (57%) with lowvision were being taught to read using brailleonly, even though 110 (79%) had the potentialto read N5-N8 print, and a further 9% had thepotential to read N1O-N36 print.

DiscussionThe schools for the blind included in the study(two in Uganda and three in Kenya) variedenormously with respect to size, quality ofbuildings, infrastructure, availability of teach-ing materials, facilities for recreation, numberof staff, and degree of integration of studentsinto normal schools. In all the schools severalof the teachers were themselves blind orvisually impaired. Low vision services andLVDs were not available in any of the schools.In Kenya a peripatetic special educationalisthas recently been appointed to promote educa-tional techniques for students with low vision,and an orthoptist has been appointed toinitiate low vision services. In two of theschools in the study students with residualvision were being taught to read ink print andwere given instruction on tasks of daily living,but the emphasis in all the schools was oneducation using techniques appropriate to thetotally blind - that is, braille. Although reasonsfor this were not investigated in this study thereare several factors which may be responsible.Firstly, low vision services are a fairly recentdevelopment"1 and teachers in special schoolsmay find it difficult to adapt to the newconcepts and to change their practices.Secondly, teachers may construe by implica-tion that the methods they have used in thepast were wrong. Thirdly, in many schoolsfor the blind a significant proportion of theteachers are blind or visually impaired them-selves and it would be difficult for them tochange to sighted methods of teaching.Fourthly, few materials and facilities are avail-able for low vision education. In this study57% of students with low vision were beingtaught to read using braille only, even though79% were capable of reading N5-N8 print.There is a need to improve awareness in

818



j.com/

Br J O


eptember 1995. D

ownloaded from

http://bjo.bmj.com/


Table 7 Effectiveness of locally produced CBM low vision devices compared with Britishstandard low vision devices (LVDs)

Near visual acuity (VA) with Group 3 Group 6 Group 7locally produced LVD (NS-N8) (NIO-N36) (-N48) Total

Same near VA with same power local LVD 22 0 0 22Same near VA with higher power local LVD 11 0 0 11Worse nearVA 6 0 0 6Local produced LVD of no benefit 7 3 1 11Total 46 3 1 50Needs met by locally produced LVD (O/6) 71-7 0 0 66-0

parents and teachers involved in special educa-tion in developing countries, emphasising thatchildren with low vision can and should usetheir residual vision wherever possible. Thereis also a need to provide appropriate low visiontraining, facilities, and educational materialsfor teachers and pupils.

NEED FOR OPTICAL SERVICESMore than half the students with low visionhad spherical or astigmatic refractive errors ofmore than 2 dioptres. In 59 students the visionimproved with spectacles and one third (46) ofstudents required new spectacles. At least 20%of the total blind school population included inthis study could benefit from new spectacles.Accurate refraction of children with highrefractive errors often in association withmedia opacities is not easy and requires experi-ence and patience. It is recommended thatchildren with visual handicap in schools for theblind or in integrated education be refractedannually and spectacles made available tothem at no or minimum cost.

NEED FOR LOW VISION DEVICESMore than a third of the students with lowvision in this study (50/140) would benefitfrom LVDs. At assessment 46 of thesestudents were able to read N5-N8 print. Thisperformance might not be sustained for longperiods but would allow access to most printedinformation. There was a wide range in thepower of the devices required and differenttypes ofLVDs were needed. A smaller range ofLVDs would not therefore meet all the need.Eighteen of the 50 students (36%) neededLVDs of more than +28 D. The CBM LVDsmet the need in two thirds of the students whohad the potential to benefit. However, in 22%of students higher powers were required withthe CBM LVDs to achieve the same levelof near vision as with the British devices, prob-ably because the latter have superior opticalqualities. Plastic, aspheric lenses, however,cannot be produced without sophisticated

Table 8 Corrected distance acuity in the better eye by level of near vision after low visionassessment in 140 students in Kenya and Uganda

NS-N8 N10-N36 N48 or less TotalCorrecteddistance acuity N % N % N % N %

<1/60 1 5-6 3 16-7 14 77-7 18 1001/60-2/60 15 60-0 6 24-0 4 16-0 25 1003/60-5/60 46 95-8 2 4-2 0 0 48 1006/60 or better 48 98-0 1 2-0 0 0 49 100

Total 110 78-6 12 8-6 18 12-9 140

manufacturing facilities. It is relatively easy topurchase or grind glass lenses with powers ofup to +28 D, but lenses of higher power arenot readily available and are far more difficultto produce. This will limit the range of LVDsthat can be produced locally given the presenttechnology. The LVDs being produced by theCBM optical workshop in Nairobi costapproximately £2.50 each to produce.There is debate whether schools for the

blind in developing countries should useenlarging photocopiers to produce educationalmaterials for students with low vision. Thesemachines are expensive to purchase and run,depend on electricity, need regular supplies ofpaper of good quality and standard size, andcontinued maintenance particularly in hot,dusty climates. The findings of this studysuggest that accurate correction of refractiveerrors and provision of appropriate LVDs fornear vision would provide a flexible, cost effec-tive, and sustainable alternative.

SIMPLE METHODS OF IDENTIFYING STUDENTSWITH LOW VISION WHO WOULD BENEFIT FROMLOW VISION ASSESSMENTLow vision services are in their infancy in mostdeveloping countries, and ophthalmic andoptical services scarce. To maximise resourcesthere is a need to develop simple methods andguidelines which could be used by thoseresponsible for children with visual impairmentto identify those who should be referred for lowvision assessment. In this study the majority ofstudents (14/18) with a corrected distancevisual acuity of less than 1/60 to perception oflight could not read print of any size, suggest-ing that form vision is required before studentscan benefit from LVDs. However, 38% ofstudents with a corrected distance acuity of lessthan 1/60 had sufficient vision to perform oneor more of the simple tests of functional vision,suggesting that form vision is not a prerequisitefor independent mobility and social contact.The ability to see 1/60 or more after full

distance correction could be used to identifythose students who will benefit from low visiondevices (sensitivity 99%). If full refractionservices are not available, teachers could betaught to assess students using the three simpletests of functional which had a sensitivity of96% in identifying students who could readN5-N8 print.

SERVICE PROVISION IMPLICATIONSIn this study assessment was undertaken inclassrooms and seven students could not beassessed for LVDs because of additionalhandicap, or because they were too young. Asconsiderable motivation, manual dexterity,time, enthusiasm, and concentration arerequired on the part of the child as well as theoptometrist during low vision assessment, thisshould be undertaken in a conducive environ-ment.

For low vision devices to be used effectivelysupport, training, follow up, and maintenanceare needed, particularly for younger children7 12

819



j.com/

Br J O


eptember 1995. D

ownloaded from

http://bjo.bmj.com/


Table 9 Results of tests offunctional vision in 140 students with low vision in Kenya andUganda

Failed all Performed Performed Performed allthree tests one test two tests three tests

Near vision Total N % N % N % N %

N5-N8 110 5 4-5 0 0 12 10-9 93 84-5N1O-N36 12 2 16-7 3 25-0 1 8-3 6 50-0N48orless 18 11 61-1 3 16-7 2 111 2 11.1Total 140 18 12-9 6 4-3 15 10-7 101 72-1

and those with lower levels of acuity. In additionmany students will need to be re-educated as'sighted' rather than 'blind'. With high powerdevices more supervised practice will berequired, and greater motivation on the part ofthe user.For low vision services to become widely

available to children with low vision in devel-oping countries there is a need to (1) developsimple guidelines for identifying students withlow vision who require assessment, (2) definethe level of training required to undertake lowvision assessment, (3) develop simplifiedmethods of assessing students with low visionwhich can be used by 'non-experts', as well as

guidelines on prescribing, (4) develop simpleguidelines on training in the use and main-tenance of LVDs, (5) modify and promote theproduction of locally produced LVDs.

To provide sustainable, low cost, lowvision services close cooperation betweenoptometrists, optical technicians, ophthal-mologists, teachers, and parents will be essen-tial.We are grateful to Combined Optical Industries, who donatedsets of low vision devices for the assessments; to Keeler, whodonated Sonksen-Silver acuity cards; and to the staff andstudents at the schools. The study was funded by the PeelMedical Trust, 'Help a Child See', Christoffel Blindenmission,Germany, and Sight Savers, UK.

1 The management of low vision of childhood. Proceedings ofWHO/PBL Consultation Bangkok, July 1992. Geneva:WHO, 1993.

2 Fagan T, Kenya: African report. Jf Vis Imp Blindness 1992;86: 16.

3 Spoerer P. How to make spectacles at low cost. Bensheim,Germany: Christoffel Blindenmission, 1994: 161-71.

4 British Standard No 7522, 1992. Part 1: Hand and standmagnifiers. London: British Standards Institution.

5 Jalie M. The principals of ophthalmic lenses. Vol III. London:Association of Dispensing Opticians, 1969: 546-56.

6 Bennett AG. Ophthalmic test types. BrJ Phys Optics 1965;22: 238.

7 Nott J. The use of low vision aids by children under the ageof seven years. BrJ Vis Imp 1994; 12: 57-9.

8 Bullimore M, Bailey I. Evaluation of new optical aids fromCOIL. Optometry Vis Sc 1989; 66: 766-73.

9 Leat S, Rumney N. Modulation transfer function of lowvision aids. Applied Optics 1992; 31: 3637-45.

10 Gilbert C, Foster A, Negrel D, Thylefors B. Childhoodblindness: a new form for recording causes ofvisual loss inchildren. WHO Bull 1993; 71: 485-9.

11 Silver J. The place of optimum low vision aids in themanagement of visual handicap. MPhil Thesis, CityUniversity, 1976.

12 Leat S, Karadsheh S. Use and non-use of low vision aids byvisually impaired children. Ophthal Physiol Opt 1991; 11:10-21.

820



j.com/

Br J O


eptember 1995. D

ownloaded from

http://bjo.bmj.com/

acuity li% $e. - bmj

Documents