Macular function tests

A presentation on Macular function tests.

1. MACULAR FUNCTION
TESTS
Dr Saurabh Kushwaha
Resident (Ophthalmology)

2. SCOPE
Macular function tests -uses and classification
Photostress test
Amsler grid
Two point discrimination test
Maddox rod test
Entoptic phenomena
Laser Interferometry
Microperimetry

3. MACULAR FUNCTION TESTS
Uses:
•Fordiagnosing
•Forfollowupofmaculardiseases
•Forevaluatingthepotentialmacularfunctionineyes
withopaquemediasuchascataractanddensevitreous
hemorrhage.
•Asapreludetosurgery,inordertoprovidea
preoperativeprognosisforthecondition.

4. CLINICAL ASSESSMENT
OF THE MACULA
Symptoms:
•Blurredvisionanddifficultywithclosework
•Scotoma
•Metamorphopsia(distortionofperceivedimages)
•Micropsia(decreaseinimagesize)
•Macropsia(increaseinimagesize)
•Colourdiscriminationmaybedisturbed,butisgenerally
lessevidentthaninevenrelativelymildopticneuropathy.
•Difficultiesrelatedtodarkadaptation,suchaspoorvision
indimlightandpersistenceofafter-images

5. MACULAR FUNCTION TESTS
MFT
MFT with
clear media
MFT with
opaque media
Depending on ocular media
Electrophysiological
tests
Psychophysical
tests
Depending on technique

6. MFT WITH CLEAR MEDIA
Visual Acuity
ColourVision
Photostresstest
Amslergrid
Two point discrimination
Microperimetry
FFA
OCT

7. MFT WITH OPAQUE MEDIA
Laser interferometry
Potential visual acuity meter test
Entopic phenomena
ERG
EOG
VEP

8. PSYCHOPHYSICAL TESTS
Subjectivetest
Aphysicalstimulusispresentedandpatientindicates
verballyorbyothersubjectivemeans,hisdetectionofthe
stimulus
Theyareasfollows:
•Visualacuity
•Colorvision
•Photostresstest
•Amsler’sgrid
•Twopointdiscriminationtest
•Entopticimagery
•MaddoxRodtest

9. ELECTROPHYSIOLOGICAL TESTS
Objectivetests
Astimulusispresentedandaresponseparameteris
measuredbyelectrophysiologicalmeans
Oneofthemosteffectivemodesoftestingformacular
functionsineyeswithtotalmediaopacities
Theyareasfollows:
•Electroretinogram(ERG)
•Electrooculogram(EOG)
•Visualevokedpotential(VEP)

10. PHOTOSTRESS TEST
Differentiatesvisuallosscausedbymaculardisease
fromthatcausedbyanopticnervelesion
Principle:
•Thevisualpigmentsarebleachedbylightwhich
causesatemporarystateofretinalinsensitivity,
perceivedbythepatientasascotoma.
•Therecoveryofvisionisdependentontheabilityof
thephotoreceptorstore-synthesizevisualpigments.

11. Thetestisperformedasfollows:
•BCVAisdetermined
•Ptisaskedtofixateonthelightofapentorchoran
indirectophthalmoscopeheldabout3cmawayfor
about10seconds.
•Photostressrecoverytime(PSRT)ismeasuredby
thetimetakentoreadany03lettersofthepre-test
acuityline.
•Testisperformedontheother,presumablynormal
eyeandtheresultsarecompared.
•Inapatientwithmacularlesion,thePSRTwillbe
longer(50secondsormore)ascomparedwiththe
normaleyewhereasinapatientwithanopticnerve
lesiontherewillbenodifference.

12. AMSLER GRID
ThegridwasdevelopedbyMarcAmsler,aSwiss
ophthalmologist.
Itisagridofhorizontalandverticallinesusedto
evaluatethe20degreesofvisualfieldcenteredonfixation.
Thereare07charts,eachchartconsistingof10cm
square.
Itisadiagnostictoolthataidsinthedetectionofvisual
disturbancescausedbychangesintheretina,particularly
themaculaaswellastheopticnerveandthevisual
pathwaytothebrain.
Presenceofabnormalitieslikeblurredareas,holes,
distortions,orblankspotsarenoted

13. Chart1
•Firstgridisstandardgridthattestsforanygeneral
subjectivepatientresponsestofaultsordistortionsin
thepattern.
•Whitelinesonablackbackgroundandacentralwhite
dotonwhichthepatientfixates.
•Gridencloses400smallsquares,eachsquare
measures5mm
•Whengridisheldat30cmfromthepatient,each
squaresubtends1degreeontheretina.
•Ifptreportsonthefirstchartthat
hecannotseethecentralwhitespot,
thisindicatesascotoma.

14. Chart2
•Thischarthasdiagonallineswhichhelpmaintain
centralfixation.
•Ifptreportsonthefirstchartthathecannotseethe
centralwhitespot,thisindicatesapositivescotoma.
•Thishelpsthempointoutthelimitsofthescotoma.
Chart3
•Ithasredlinesonablackbackground
•Helpfulindetectingcolorscotomasand
desaturation,thatmayoccurinopticnerve,chiasmalor
toxicamblyopiarelatedproblems.

15. Chart4
•This chart comprises random dots only
•used to differentiate scotomafrom metamorphopsia
Chart 5
•This chart has horizontal lines
•helps detect metamorphopsiaalong specific meridians

16. Chart6
•Thischartissimilartochart5buthaswhite
backgroundandcentrallinesareorientedcloserfor
detailedevaluation
Chart7
•Thischarthasfinecentralgrid
•Eachsquaresubtendsanangleofhalfadegree
whenthechartisheldat30cmfromthepatient

17. Centralscotomaas
seenbyapatient
Forexamplethis
mightbesecondaryto
centralareolarchoroidal
dystrophyorcongenital
toxoplasmosis.

18. Aspaceocuupyingpathology
suchasatumorthatforcesthe
conesclosertogetherwillcause
thegridtobeseendistorted.
Theretinalimagewillfallon
moreconesthannormalandthe
linesoftheAmslergridwillbe
seenaslargerandbend
outward.
Thisisknownas"macropsia"

19. Apatientwithmacular
edema oranyother
pathologythatforcesthe
conesapart.
Theretinalimagewill
stimulatefewerconesthan
normalandthelinesofthe
Amslergridwillbeseenas
smallerandtendtobend
awayfromthepatient.
Thisconditionistermed
"micropsia".

20. A combination of
squeezingandspreadingof
theconescausesanoverall
distortionoftheimage.
ThelinesoftheAmsler
gridbecomedistortedand
non-uniform.
ThisconditionIstermed
Metamorphopsia.

21. TWO POINT DISCRIMINATION TEST
Theabilitytodistinguish2illuminatedpointsoflight2
mmdiameterinsizeand2inchesapart,placed2feet
awayfromthepatient’seyesuggestsgoodretinal
functions.
Excellentmethodfortestingmacularfunctionsin
childrenanduncooperativeadultsintheoutpatient’s
clinic
Ideallybeperformedinallpatientsduringinitial
examinationoftheeye

22. MADDOX ROD TEST
Itisahighpowercylindricallensusedtoformaline
imageperpendiculartotheaxisoftheparallelcylinders
fromapointsourceoflight.
Thelightsourceplacedbetween33cmto40cminfront
ofeacheyetogetappropriateobjectiveresults.
Anybreaks/holes;discoloration/distortioninthisline
indicatesamacularlesion
Thisisaverysensitivetestthatcanbeperformedinthe
outpatientclinicwithoutrequirementofanyspecific
equipment.

23. ENTOPTIC PHENOMENON
Entopticphenomenonisreferredtovisualperceptions
thatareproducedorinfluencedbythenativestructuresof
one’sowneye.
Illuminationofthefundusbyparallellightraysallows
visualizationofsmallopacitieslocatedclosetotheretina.
Sincethecolumnsofbloodcontainedwithinretinal
bloodvesselsarelinearopacitiessituatedinfrontofthe
retinalphotoreceptors,thismakesretinalbloodvessels
visible.
Ifafocalsourceoflight(suchassmallpenlight)is
pressedfirmlyagainsttheexterioroftheeyethrough
closedlids,thearborizingpatternofretinalbloodvessels
canbebrieflymadevisible.Thistestisusedastestof
retinalfunction.

24. ENTOPTIC PHENOMENON

25. Thebluefieldentopticphenomenon(flyingspots)
perceptionisperformedinthefollowingmanner:
•Ifonelooksatabrightanddiffuselyilluminatedsurface
withnocontrastingfeatures,aseriesoffastmoving,
luminouspointsareseenwhichtendtomoveinagenerally
curvedpattern,withtrailingshort,taperingsegmentsbehind
them.
•Thespotsarebestseenifthebackgroundisilluminated
bybluelightinthespectralregionof350to450nm.
•Sincethisregioncontainsthespectralabsorptionpeakof
hemoglobin,themovingparticlesrepresentredbloodcells
passingthroughtheretinalcapillaries.
•Normally-15ormoreofmovingcorpusclesareseen.
•Abnormalbluefieldentopticphenomenon-failuretosee
anycorpusclesorpartiallossofcorpusclesinonepartof
thefield,visibilityoflessnumberofcorpusclesandslow
corpuscularmovement.

26. HAIDINGER’S BRUSHES
Ifoneviewsadiffuselyilluminatedsourceofplane
polarizedwhiteorbluelight,brushesradiatingfromthe
pointoffixationintheformofMaltesecrosscanbeseen.
Thebrusheshavecontrastingyellowandbluehues.
ThedarkerportionsoftheMaltesepatternareyellow,
whereasthebrighterportionsareblue.

27. Thisphenomenoniscausedbyvariationsin
absorptionofplanepolarizedlightbyorientedmolecules
ofxanthophyllpigmentinthefovealretina.
Iftheyellowpigmentarrangementinthefoveais
disruptedbypathologyintheinnerretinallayers,the
brusheswillnotbeseen.
Commonlyusedasascreeningtestforretinal
pathologyinstrabismuspatientswithamblyopia.

28. LASER INTERFEROMETRY
Theresolvingpowerofthemaculaistestedbyusingtwo
coherentbeamsoflight,whichcreateathree-dimensional
fringepatternontheretina.
Thebeamsproducetwopointsourcesbehindthelens
opacity;thelightwavesemittedfromthesetwopoints
overlap.
Wherethecrestofonewaveoverlapsthetroughofthe
other,theeffectiscancelledandablackbandisproduced.
Wherecrestsortroughscoincidewithoneanother,the
enhancementproducesbrightbandsoflight.
Laserinterferometrycanthusbeusedineyeswith
immaturecataracts.

29. Thetestisperformedasfollows:
•Pupilsarewidelydilatedandlightbeamisdirectedinto
thecentreofthepupilintheplaneoftheiris.
•Thepupilisscanneduntilthefringepatternisseenand
patientindicatestheorientationofthebandsoflight.
•Initially,largegratingsareusedandthengradually
diminisheduntilpatientisunabletodetectcorrect
orientation
•Thepotentialvisualacuityisestimatedfromthewidthof
thegratingsresolved.
•Lasergeneratedfringesarenotdependentontheoptical
componentsoftheeyeforfocusing.Therefore,ametropia
haslittleinfluenceonthepatternsproducedbyretina.
•Italsoover-predictsthevisualpotentialinamblyopic
eyesbecauselaserfringevisionisbetterthantheletter
acuity.

30. POTENTIAL VISUAL ACUITY
METER
Thepotentialacuitymeter(PAM)projectsstandard
Snellenchartthroughasmallclearareaofanimmature
cataract
MaincomponentsofPAMareabrightlightsource,
miniaturetransilluminatedSnellenchartanda+12Dlens.
Mostaccuratewithvisualacuitiesof6/60orbetter.
Inperformingthetest,thepupilsshouldbe
widelydilatedandthepatientisaskedtoread
thelettersonthechartandthelevelrecorded.

31. MICROPERIMETRY
Alsok/asfundusperimetry,itallowsforexact
topographiccorrelationbetweenfundusdetailsanditslight
sensitivity.
Theprinciplerestsonthepossibilitytosee,inrealtime,
theretinaunderexamination(byinfraredlight)andto
projectadefinedlightstimulusoveranindividuallyselected
location.
Becauselightprojectionisjustrelatedtopreviously
selectedanatomicallandmarksandisindependentof
fixationandanyothereyemovement,theexaminerobtains
thefunctionalresponseoftheselectedarea.
Thecharacteristicsoffixation(locationandstability)are
easilyandexactlyquantifiedwithmicroperimetry.

32. Automaticfollow-upexaminationquantifiesretinal
thresholdexactlyoverthesameretinalpointstestedduring
baselineexamination(eveniffixationchangesduring
follow-uptime).
Staticmicroperimetryismorecommonlyused,buta
kinetictestisalsoavailable.

33. CONCLUSION
Evaluationofthemacularfunctionofapatientwith
opaquemediaisacommonlyfacedchallengingproblem
Nosingletestisimpeccable

34. THANK YOU