Visuel field test as a routine during ophtalmological examination of EPI villages

WORLD HEALTH ORGANIZATION ORGANISATION MONDIALE DE LA SANTE 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 visualfield 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 of the test as a routine. In the original pilot study the population aged. over 10 years of the villages were subjected to visual fieltl. test. fhe questions consid.ered. are: 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 factthat the test is time ccrnsuming and yet potential canclid.ates should not be left out? 1. Assuming that the test is feasible ancl useful how best coulti the results be reported. without jeopard.izing the importance of comparir:g present with past results? 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 seenin the table and it is the six.th which is the addition to the table hithertoin use. ILte prevalence of blindness. without application of visual fieldtest is hi$, l.o/o arfi. with it, i-t increases to to.g/o. clearly J.f16 of tbepopulation who are functionatly b1ind. wou1d. have been overlooked in the assessment of the prevalence of blindness in this village if visual fielcltest 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 specificprevalence rate of blindaess is consid.eredra high rate of fwrctionallyblind 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 testfor 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. 20bservallion 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 an area of vector control. Bulletin of the l'Ior1d' Eealth 0rganization, 58 (1) 10?-112 (rgeo). ROLLA\ID A. & TIIYf,EFORS B. Aspects 6volutifs d.e ltonchocercose oculaire en Afrique occj-dentale, aprbs trois ans de lutte antisimrLi&ienne. rropenm6d.izin und parasitotogie, 10, 482-4eO (1979). nADZlS KoYo e ROLLAIID A., TE$,EFORS 3" The evolution of ocular onchocerciasis :n lfre Volta River Basj-n a,rea over a period. of five years of vector control. (:n press). Table I EYALUATION CF' ]TTI,TAGEOPHIHATMOTOGICAT RESlIf,T AFltsR NETATIED Country : IvIaIi Viilag€ : Ivlana,mboug:ou AGE lTo. examined. Qrhthalmolo.gically 0cuIar Onchocer- ciasis Severe 0nchocercal Ocu1ar lesion Tmpairnent of vision Blinclness(without visua: field test) Blindness(vtttr ltsual field test) 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 14 rl M F },I F }I F M F 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 26 L1 3 2 5 4 t, 9 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 the census populatiorn. lhd F l* Efi E TJ E C) Edohd Id }JEIrl EilcnHrdolrl HtdFTF EH BEU)f4aHU] =fi>BHtsiH 1EHUl-l!q<H9H IO c)cjO€ Hz< c) F{aF3dfrt- EY rn|td EH crl uaaHOHZHaB F E4g E a) r-1 h-t F 0) <+ o a{H. ct rr P, a I, A,P Fr H. oHp ql' o a cl- PREVALmTCE nAIES 0F BIJININESS \, E E EIoI EIH E E t, c{o hdo H tstdo(= C]oq F A' c+ o @{F <+ o tr ct P. TA n s,H F+) P. oHp cl' o(o cl PREVAIM{CE RtrIES OF SLINDNESS vIE ohdhdH €< HEBZC)<trH HFd EE c)Edtd s)a oHrd td VE aaE,c) trlEbcnoza Ed tJ {ooH BHEIdH>6ZZF"ru HEEazBU>ltlEdOC)FqEhdEHH<E<tr:dHE*H HtJ BHi7l Ed pE6g \n c/lF] * bd !dbtr|!CN rN CIHoEqu p(IE Eq)I Eo F E c)F =oz() ozOfr bd fd 0)t o a{P.+ ot+ H.(D npF F+) ts oHa cl o u cl td tDct o a {P. cfp ts a ng) P FIJ P. oPp ct o tu <+ hd h-f* IH H HF.)bl1E)c)jtr, lp{E{ ETJ1A )c) ,fd t td .t uiHzIrJ ta1atu) )H{Flt!E .,8 lut{ ,H €)Elo lF:l i<IHardt> , t:l Its iH!uru ,€ ETaB E{ad Ea o rd a H H E-iHE C E4(n ts dUH H o E E HEfr @ H E;U' ot{ 6 c)BoN c) 2H Fdo rr !d s, <f o a {F. ct o trct P.(otp H |-+, l-r. oFp + oa * n s) * o(J' {P. cl' Er H. ln EF r-t H. oHp + oa G+ PREIIATM{CE HATES OF BL]NDNIESS E E 6)Ia