routine. In

ORGANIZATION

COIfFIEOL PR0G?"LMIII RIYEN. SASII{ ^..I.RT.\.

O}ICJ]OCEtCTJ,SIS

I}I frffi ^VOLTA

EXPM.T -IDV]SCRY COII,{ITTEE

For;rth session

furaa!9r_-2-6-j-Q_f-9pla1ql--e:])pz

CEIG]ldl.T, : ^E]'IGIfSH

ocPfB.^"c4.2

(ocr/aT.2)

VISUXI F]XID ItrST JIS .i ^RO-UT]IiE DINING

OPHT'u,*tLi' iOL 0G IC:il EX,LMIirIltT I 0II ^OF ElrI ^V ILI-:GES

J. corlplete assessrnent of visual function includ.es a test for cenf,ral as wel-I as peripheral vision. Central visj-on is com:only assessed by the

visual acuity test using Snellens test types but peripireral vision is by

the visual field test. ^:4:ereas visual acuity test in its adapted forrn can

be taught ^'bo illiterates wleo are unfa.miliar with the proced.ure to enable

acquisition of sufficiently reliable results in ^{a short} tine, visual field.

test is usually tine consur.ling and more d.ifficult to ^perform as it ^demands

Elore cooperation from the patient. For this reason visual field test r:rrlike visu-al acuity test is not usually d.one as a routjne.

fn the definition of blindness both central as well as peripheral vision are taken into account. Thu-s'[I0 d.efini-tion of blind.ness says inability to recognize fingers at ] ^{rnetres v,'ith} the better eye or the red.uction of visual field to less than lOc of fixation. This is also the defiirition ^followed. by

the ^OCP in the village evaluation. IIowever, estination of blindness by rneans

of visual fieId. test has hitherto not been practised. as a routjne for reasons

already elaboratcd. fn view of the fact that onchocercal choroido-retinitis

d.cstroys the retina, restricti-ng visual field.s, just as d.oes optic atrophy,

it follorvs that prevalence rates of blindness calculated. r,rithout taking visual field. test into ^{account give} an underestl'na'cion of the rates.

The evaluation of ocular onchocerciasis 1 ^years and 5 years after vector.control in the Volta River Basin area has shovrn that whereas lesions

of the anterior segraent of the eyes have stabilized, those of the posterior segnent continue to ^progress to a 1l'nited. extent. fne need. to follow up and. d.ocument the developnent of these lesions na"kes routine visua.l field tests now so essential in the epid,eniologicar and ophthalmological

examina'uion of ^OCP.

2-

I{aterial ^{and Ivletho€}

For more than a year now, visual field. tests with Sjerrr:nts targent scxeen and. tr'riednanrs anal5rser have been canietl out dr:ring the rr,sual EPf d.etailed. evaluation of villages to ^assess the

feasibility

routine. In

pilot

the

of the villages were subjected to visual fieltl.

test.

1. rs the population in question rea11y capabre of und.erstand.ing

the test ^procedure and. of turning out adequate and. reproduceable results?

2. hrhat should. be the inclication for the test in view of the fact that the test is time ccrnsuming and yet potential canclid.ates should not be left ^out?

1.

is

Results

Tabre r illustrates a tabre which is being proposed. for use in reporting on ophthalmological results which i:eclude the results of visual fieId. test ^wtren done as a routine. Ehis table gives the results of a hlrperend.en:ic village of Mananbougou in l*{a1i, on ttre river Nageg where

there is ^an on-going transmission of onchocerciasis. Six co}:nns are seen

in the table and it is the six.th which is the addition to the table hitherto in use. ILte prevalence of blindness. without application of visual field test is hi$, l.o/o ^arfi. with it, i-t increases to to.g/o. clearly _J.f16 of tbe population _who are functionatly b1ind. wou1d. have been overlooked in the assessment of the prevalence of blindness in this village if visual fielcl test had not been carried. out.

Table ff illustrates the results of Manambougou and two other neigh- bouring villages pooled together. Tais is to show that if age specific

prevalence rate of blindaess is consid.eredra high rate of fwrctionally blind ^people are masked in the 3€'e group of 15-49 than jrr _{the group aged} l0 ^{years and. above. This wou1d. suggest,} consid.ering the d.efinition of blindness by the use of visual acuity aIone, that the visual field. test also d.etects bIi.:nd.ing cand.id.ates early, since cand.id.ates with restrictj.on of visual fieId. lose thei: central vision with time.

Fig::res f, fI and IIf sh.ow by histogran the prevalence rates of blindness estimated with and without the results of visual field test for comparisorr in 1J villages r+trich have had visual field tests ^d.one since the inclusion of the test as a routine in the ophthalnorogical evaluation of ^EPI vi3-1ages.

0bservallion arrd. 4iscqss ion

A revj.ew of the results of visual field. tests d.one on the ^population

a6ied over I0 ^years ln the two villages ^{showed an} untestability rate of about 1Of. ^A cand.id.ate was declared as untestable if he couId. not be made to und.erstaad. the test or ^could. not be nade to ^{give reli.abIe a;r.swers}

which the test demantl.ed., d.espite the fact that there existed. no apparent

clinical rea^son to explain the lack of cooperation. Compared with visual acuity test ^{which gives} up to about M r:ntestability rate, this test ^can

be consid.ered. as acceptable as a routine test. ^{Thus the} test is feasible

i.:n the population concerneil.

In ord.er not to have to ^spend. too long a time at the village d.uring d.etailed. evaluation whilst havi-ng to do visual field. testr the factor of a6e at which the test ^was to ^{be d.one was} consid.ered.. Age 15 wa.s set as

a safe age below which there would be no risk of omitting a potential posterior segment lesion, but the number of tests to ^{be done was} stiII too large. ft r,ras therefore d.ecid.ed. to follow the usual ophthalnological pra.ctice in the ind.ication for visual fieltl. test. ^Ihus it was only

patients with ophtha'lnoscopically visible onchocereal lesion of the

posterior segment of the eye, who r:nderwent visual fielcl test' ^With this indication the time factor ^{ha^s been resolved} whilst not risking leaving out a candidate who shanld need the test.

Reporting of the results ^achieved. W ^the fact that ^a candidate found. blind. by visual field. test ^would. not have been classified. ^{a.s such} otherwise. Since the prevalence rates are given as the m:mber of ^cases

found. compared with the number at risk, a table ignoring the results ^of visual fieId. test ^gives results that can compare with past results. ^The

proposed. table f has the advantage that the first five coh:mns show the para.meters which aIlow comparison with past results. ^The additional

coh:mn six ^shows the tnre prevalence of blindness by ful1 d.efinition.

fhus the two prevalent rates elxe presented. simultaneously for comparison.

Incorporatirrg visual field. test ^{as a} routj::e in the EPI ophthalmo-

logical exaarination in the foru that has been elaborated. has the ^advantage of unveiling many more blinct by clefinition than it has been shoun and has been believed. to exist jl ^oncho area.s. But above all, this test will help to ^follow up accrrately the evolution of onchocercal lesions of the

posterior segment of the eye. ^The inportance of accurate documentation

of the d.evelopment of the lesions of the posteri.or ^seguent of the eye at this time cannot be und.erestimated as this ^nay influence future stratery of onchocerciasis control.

-4-

Rgferences

TIIYLEFORS B. & foNJUM A.M. A 1-ye* ^fo11ow-up of ocular onchocerciasis

in

control.

ROLLA\ID A. & TIIYf,EFORS

B.

trois

lutte

rropenm6d.izin und parasitotogie, 10, ^{482-4eO (1979).}

nADZlS KoYo e ^ROLLAIID A., ^TE$,EFORS

3"

onchocerciasis :n lfre Volta River Basj-n a,rea over a ^period. of five

years of vector control. (:n press).

EYALUATION CF' ]TTI,TAGE OPHIHATMOTOGICAT RESlIf,T AFltsR NETATIED

Country

:

Viilag€

:

AGE

lTo. examined.

Qrhthalmolo.

gically

0cuIar Onchocer-

ciasis

Severe 0nchocercal Ocu1ar lesion

Tmpairnent

of vision

Blinclness (without visua:

field

Blindness

(vtttr ltsual

field

M F M F M F M F M F M F

,-9 ^L5 t4 5 1 0 0 0 0 o 0 0 o

10-14 14 11 10 ₉ 2 1 0 0 0 0 o 0

L5-29 ,, 5t ²⁹ 2t 9 2 0 0 2 1 4 ²

3o-49 24 22 t9 t4 B 7 o 1 2 2 5 4

5o+ t7 75 11 _{9 9} 4 5 5 9 5 11 ₇

TOTAT to, 94 59.?rt _57.4/o 27.2/o t4.y/, _4.f/o 6.#/o B.ryo 5.qo ^L2.T/o 9.o/o

t97 54.Oi 2t.7/o _{5.6% 7.CI/o 1.:O.go}

Censns populationl _1A2

Prevalence of blindness relates to the census population.

Table If

POOLED OPEIIHALMOLOGICAI RESUTTS MAI{AI,IB0UGCTU + TOULAI,IAMJ0 +

otrl 'FnH ^VTLLAGES FOUTABOUGOU

AGE

No. exa.mined.

Ophtha'lme16-

gicaJ.ly

Ocular Orrchocer-

ciasis

Severe Onchocercal Ocular lesion

TmFai:ment

of vision

Slindness without visual

fielcL test)

Slindaess

(with visual field test)

M

r

5-9 ^{25 20} 4 ^{1 o o o} o 0 0 0 o

10-14 L6 22 11 L6 2 2 1 0 0 0 0 1

t5-29 _{44 54 15} 3B 11 4 ¹ o ^{2 1} 4 ,

10-49 46 42 4t

,t

t,

5o+ ^{26 2g 20 20} L' t1 ⁶ 12 t4 ^{B L7} 11

TOI'AL 158 ]'67 _70.9/o 61.f/o ,2".flo L9.2/o 7.0/o 8.4y, 9.lYo 5.A/o ^14.CI/o g.g,

125 ⁶⁷ .1yo 25.e/o l-7,t% _7.CI/o LL.frt

Census populati.on z JO2

Prevalence of blindness relates

to

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