the neurological examination special senses assessing ... · special senses assessing vision and...
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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