TheNeurologicalExaminationSpecialSenses

AssessingVisionandhearingDr.TamaraAlqudah

THEOPTICSOFVISION

RefractionofLight

Therefractiveindexofatransparentsubstanceistheratioofthevelocityoflightinairtothevelocityinthesubstance

Themorealensbendslightrays,thegreaterisits“refractivepower.”Thisrefractivepowerismeasuredintermsofdiopters.Therefractivepowerindioptersofaconvexlensisequalto1meterdividedbyitsfocallength

1/1=

1/0.5=

1/0.1=

Vision

Abouttwothirdsofthe59diopters ofrefractivepoweroftheeyeisprovidedbytheanteriorsurfaceofthecornea

Accommodation• Theabilityoftheeyetochangeitsfocusfromdistanttonearobjectsandviceversa.Thisprocessisachievedbythe lenschangingitsshape.

Accommodation

Presbyopia:Lossofaccommodationbythelens

Errorsofrefraction

Inhyperopiatheeyeball istooshortorthelenssystemistooweak.

Inmyopiatheeyeballistoolonganeyeballorthelenssystemistooactive.

VisualAcuity• Visualacuityreferstotheabilityoftheeyetoappreciatetwopoints1.75mmapartastwodistinctpoints(clarity ofvision).

• Assessmentofvisualacuityismandatoryinallophthalmicpatients.Eacheyemustbetestedseparately.ThemostcommonlyusedmethodoftestingisusingaSnellenchart,whichdisplaysarandomselectionoflettersatdiminishingfontsizeinsuccessivelines.

• Eachlineismarkedwithanumber(60,36,24,18,12,9&6).Thisrepresentsthedistanceinmetersatwhichanormallysightedpersoncouldreadthatline.

• Placepatient6metersawayfromthechart• Eacheyeneedstobetestedseparately• Useanoccluder tocovertheeyethatisnotbeingtested

• Askpatienttoreadfromthetopletter• Keepgoinguntiltheycannotreadthelineclearlyortheymake2ormoreerrorsinaline.

• Thepreviouslineisthelineyoudocument• TheresultisexpressedasaratioX/Y,whereXisthetestingdistanceandYreferstothelinecontainingthesmallestletterthatthepatientidentifies.

• Ifthepatientcannotreaddowntoline6(6/6),placeapinholedirectlyinfrontoftheeye tocorrectanyresidualrefractiveerror.

• Ifthevisualacuityisnotimprovedwithapinhole,thisindicatesthepresenceofeyediseasenotrelatedtotherefractiveapparatusalone,suchasretinaloropticnervepathology.

• Ifthepatientcannotseethelargestfontletter,reducethetestdistanceto3meters,thento1meterifnecessary.

• Iftheystillcannotseethelargestfontletter,documentinsteadwhethertheycancountfingers,seehandmovementorjustperceivethedifferencebetweenlightanddark.

• Thepowerofthelensneededtocorrectthevisualacuityproblemisdeterminedbytrialanderror

Jaegar eyechart•TheJaegereyechart(orJaegercard)isusedtotestanddocumentnearvisualacuityatanormalreadingdistance.Ithasprintsamplesofdifferentsizes(No.1-No.11).Anyonewithnormalvisionshouldbeabletoreadthesmallestprintingoodlighting,atacomfortablereadingdistance.

1. Askthepatienttoholdthetestcard37cmawayfromtheeyes.

2. Testeacheyealone.3. Askthepatienttogotothesmallestblockof

texttheyfeelcanseewithoutsquinting,andreadthatpassagealoud.

4. Askthepatienttocontinuereadingsuccessivelysmallerblocksofprintuntilhereachesasizethatisnotreadable.

5. Recordthe“J”valueofthesmallestblockoftexthecanread

Colorvision• Theretinacontainstwotypesofphotoreceptors;the rodsand cones.

• Conesareresponsibleforcolorvision.• Therearethreetypesofcones,eachcontainingaspecificphotopigment calledanopsin thatismostsensitivetoparticularwavelengthsoflight( blue,greenandred).

• Thebraincombinesinputfromallthreetypesofconestoproducenormalcolorvision.

445 535 570

ColorVisionDeficiency• Colorvisiondeficiency (colorblindness)representsagroupofconditionsthataffecttheperceptionofcolor.

• Red-greencolorvisiondefectsarethemostcommonformof colorvisiondeficiency.Affectedindividualshavetroubledistinguishingbetweensomeshadesofred,yellow,andgreen.ItisanX-linkedgeneticdisorder.

• Apersonwithlossofredconesiscalledaprotanope

• Apersonwholacksgreenconesiscalledadeuteranope

• Bluecolorvisiondefects(tritanopia),whicharerarer,causeproblemswithdifferentiatingshadesofblueandgreen. DefectinChromosome7

• Usually,color deficiencyisaninheritedcondition.Butdiseaseorinjurythatdamagestheopticnerveorretinacanalsocauselossofcolor recognitioninsuchcasetheconditionmightaffectoneeyeonly.

Howtotestforcolorblindness

• Thepatientisshownaseriesofspeciallydesignedpicturescomposedofcolored dots,calledpseudoisochromatic plates.MostcommonlyusedisIshiharatest.

• Thepatientisaskedtolookfornumbersamongthevariouscolored dots.Individualswithnormalcolorvisionseeanumber,whilethosewithadeficiencyseeadifferentnumberorseenothingatall.

• Testeacheyeindividuallyandensurethereisenoughsunlightintheroom.

74vs 21

42VS4“green”/2“red”

Assessinghearing

• TypesofDeafness:1. Conductivedeafness:impairmentofear

structuresthatconductsoundwavestothecochlea.

2. Nervedeafness:impairmentofthecochlea,theVIIInerveortheCNScircuitsfromtheear.

• HearingcanbeassedbysubjectivemethodssuchasRinne andWebertests,orbyobjectivemethodssuchasanaudiometry test

WeberTest• Thetuningforkisplacedonthevertexoftheskullinthemidline,andthepatientisaskedtoreportthesidewherethetonesoundslouder.

• Normally,thetonesoundsequalonbothsides.

• Inconductivehearingloss,thetoneislouderontheaffectedside.

• Insensorineural hearingloss,thetoneislouderonthenormalside.

Rinne Test• Thistestisdesignedtoevaluatehearing• Weusea256Hztuningforkforthistest

• Weputavibratingfork1-2cmawayfromtheear(airconduction)thenweputthebaseoftheforkonthemastoidbone(boneconduction),andaskthepatienttocomparebetweenthetwosounds.Repeatfortheotherear.

• Normalindividualswillhearthetonebetterbyairconduction.

• Inconductivehearingloss,boneconductionisgreaterthanairconduction,becauseboneconductionbypassesproblemsintheexternalormiddleear.

• Insensorineural hearingloss,airconductionisgreaterthanboneconduction(asinnormalhearing),however,hearingisdecreasedintheaffectedear.

WeberTest

Rinne Test

Audiogram• Anaudiometry testshearingacuity.Ittestsboththeintensityandthetoneofsounds.

• Soundintensityismeasuredindecibel(dB).Ahealthyhumanearcanhearquietsoundssuchaswhispers,theseareabout20dB.

• Thetoneofasoundismeasuredincyclespersecond.TheunitofmeasurementisHertz.

• Normalhearingrangeis250-8,000Hzat25dBorlower.

• Thetestisdesignedtotestairconduction.• Ifairconductionisabnormalthenboneconductionistested.

• Theresultsofthetestareshownonanaudiogram.

Normalaudiogram

Rightear.Boneconductionisbetterthanairconduction.Thepatienthaslow- tomid-frequencyconductivehearinglossduetotympanicmembraneperforation.

Bilateral,noise-inducedsensorineural hearingloss.

Bestofluck