1. Electrodiagnosis tests ofElectrodiagnosis tests ofvisual systemvisual systemDr ibtisam marashdehDr ibtisam marashdeh

2. ElectroretinogramElectroretinogram(ERG)(ERG) 3. ERGERG The record of retinal action currentsThe record of retinal action currentsgenerated by the retina in response togenerated by the retina in response tolight stimuluslight stimulus objective, quantitative measure of retinalobjective, quantitative measure of retinalfunctionfunction It uses electrodes placed on the cornea orIt uses electrodes placed on the cornea oradjacent to the orbit to monitor changes inadjacent to the orbit to monitor changes inthe electrical potential of the eye inthe electrical potential of the eye inresponse to specific stimuliresponse to specific stimuli 4. The ability to distinguish between differentThe ability to distinguish between differentcell layers and cell types means thatcell layers and cell types means thatERGs can be used to distinguish betweenERGs can be used to distinguish betweeninherited retinal disorders and dystrophiesinherited retinal disorders and dystrophiesthat may otherwise prove clinicallythat may otherwise prove clinicallyindistinguishable.indistinguishable. SeveralSeveral different typesdifferent types of ERG testof ERG testprovideprovide specific informationspecific information about theabout thepatients visual functionpatients visual function 5. Full field ERGFull field ERG It provides an assessment ofIt provides an assessment of generalgeneralretinal function and can distinguishretinal function and can distinguishbetween the various cell typesbetween the various cell types,,revealing the function of photoreceptors,revealing the function of photoreceptors,bipolar cells, ganglion cells and amacrinebipolar cells, ganglion cells and amacrinecells, butcells, but no specific information aboutno specific information aboutindividual sectorsindividual sectors of the retina.of the retina. Response to change in luminanceResponse to change in luminance 6. Multi-focal ERGMulti-focal ERG which measures thewhich measures the responseresponse in each of ain each of alarge number oflarge number of small sectorssmall sectors, typically, typicallyeither 61 or 103, of the retina.either 61 or 103, of the retina. response toresponse to changes in contrastchanges in contrast It thus provides a map that allows theIt thus provides a map that allows theclinician toclinician to locatelocate specific areas ofspecific areas ofmalfunctionmalfunction 7. Pattern ERGPattern ERG measures the response to a temporallymeasures the response to a temporallychanging pattern of contrastchanging pattern of contrast at a constantat a constantlevel of luminance, providing informationlevel of luminance, providing informationaboutabout ganglion cells and generalizedganglion cells and generalizedmacular functionmacular function 8. The electro-oculogramThe electro-oculogram measuresmeasures changes in the resting potentialchanges in the resting potentialof the eye during adaptation to dark andof the eye during adaptation to dark andlight states, revealinglight states, revealing function of thefunction of theretinal pigment epithelium.retinal pigment epithelium. 9. Visual evoked potentialVisual evoked potential Gross electrical signal generated at visual cortexGross electrical signal generated at visual cortexin response to visual stimuliin response to visual stimuli RecordedRecorded by EEGby EEG It is the onlyIt is the only objective techniqueobjective technique to assessto assessclinical and functional state of visual systemclinical and functional state of visual systembeyond retinal ganglion cellsbeyond retinal ganglion cells.. 10. The typical ERG waveform is the sum result ofThe typical ERG waveform is the sum result ofactivity in the photoreceptors and bipolar cells,activity in the photoreceptors and bipolar cells,with some contribution from Mller cells. Thewith some contribution from Mller cells. Theinitial negative deflection, known as theinitial negative deflection, known as the a-wavea-wave,,is the result of early signals from theis the result of early signals from the rod androd andcone photoreceptorscone photoreceptors. The subsequent rise. The subsequent risetowards the positive peak, known as thetowards the positive peak, known as the b-b-wavewave, is created primarily by slower signals from, is created primarily by slower signals fromthethe muller cellsmuller cells and conducted by rod and coneand conducted by rod and conebipolar cells.bipolar cells. 11. Two principal measures of the ERGTwo principal measures of the ERGwaveform are taken:waveform are taken: 1) The1) The amplitudeamplitude (a) from the baseline to(a) from the baseline tothe negative trough of the a-wave, and thethe negative trough of the a-wave, and theamplitude of the b-wave measured fromamplitude of the b-wave measured fromthe trough of the a-wave to the followingthe trough of the a-wave to the followingpeak of the b-wavepeak of the b-wave 12. 2) the time (t) from flash onset to the2) the time (t) from flash onset to thetrough of the a-wave and the time (t) fromtrough of the a-wave and the time (t) fromflash onset to the peak of the b-wave .flash onset to the peak of the b-wave .These times, reflecting peak latency, areThese times, reflecting peak latency, arereferred to as referred to as implicit timesimplicit times in the in thejargon of electroretinography.jargon of electroretinography. 13. ffERGffERG ISCEV Standard ERG ProtocolISCEV Standard ERG ProtocolIn 1989, theIn 1989, the International Society forInternational Society forClinical Electrophysiology of VisionClinical Electrophysiology of Vision(ISCEV) developed a protocol to(ISCEV) developed a protocol tostandardize ERGstandardize ERG testing so test resultstesting so test resultscould be compared worldwide. Thecould be compared worldwide. Theprotocol consists ofprotocol consists of five separate testsfive separate tests,,each designed to evaluateeach designed to evaluate different areasdifferent areasor functionsor functions of the eye.of the eye. 14. Ganzfeld ERG recording setup. The ERG equipment consists ofa Ganzfeld bowl, a direct current amplifier, and a PC-basedcontrol and recording unit. 15. Dim Scotopic Flash ERGDim Scotopic Flash ERGThis is the first step in the InternationalThis is the first step in the InternationalSociety for Clinical Electrophysiology ofSociety for Clinical Electrophysiology ofVision (ISCEV) standard ERG protocol. ItVision (ISCEV) standard ERG protocol. Itis conducted with a -25 dB flash. In ais conducted with a -25 dB flash. In adark-adapteddark-adapted eye, aeye, a dimdim flash tests aflash tests aresponse arising from theresponse arising from the rodsrods primarilyprimarilyand associated glial cells.and associated glial cells. 16. Maximum Scotopic Flash ERGMaximum Scotopic Flash ERGThis is the second step in the InternationalThis is the second step in the InternationalSociety for Clinical Electrophysiology ofSociety for Clinical Electrophysiology ofVision (ISCEV) standard ERG protocol. ItVision (ISCEV) standard ERG protocol. Itis conducted with a 0 dB flash. In ais conducted with a 0 dB flash. In a dark-dark-adaptedadapted eye, aeye, a moderatemoderate flash tests aflash tests aresponse fromresponse from both the rods and cones.both the rods and cones. 17. Oscillatory Potentials (OPs)Oscillatory Potentials (OPs)This is the third step in the International SocietyThis is the third step in the International Societyfor Clinical Electrophysiology of Vision (ISCEV)for Clinical Electrophysiology of Vision (ISCEV)standard ERG protocol. The oscillatorystandard ERG protocol. The oscillatorypotentials arepotentials are high-frequency oscillationshigh-frequency oscillations ororwavelets seenwavelets seen on the leading-edge of the b-on the leading-edge of the b-wavewave. The oscillatory potentials of the ERG are. The oscillatory potentials of the ERG area sensitive and objective measure of function ofa sensitive and objective measure of function ofthethe amacrine cellsamacrine cells and become abnormal earlyand become abnormal earlyin retinal ischemia.in retinal ischemia. 18. Photopic Flash ERGPhotopic Flash ERGOrOr Single Flash Cone ResponseSingle Flash Cone ResponseThis is the fourth step in the InternationalThis is the fourth step in the InternationalSociety for Clinical Electrophysiology ofSociety for Clinical Electrophysiology ofVision (ISCEV) standard ERG protocol. ItVision (ISCEV) standard ERG protocol. Itis conducted with a 0 dB flash. In ais conducted with a 0 dB flash. In a light-light-adaptedadapted eye, aeye, a moderatemoderate flash tests aflash tests aresponse arising from theresponse arising from the conescones 19. 30 Hz Flicker ERG30 Hz Flicker ERGThis is the fifth step in the InternationalThis is the fifth step in the InternationalSociety for Clinical Electrophysiology ofSociety for Clinical Electrophysiology ofVision (ISCEV) standard ERG protocol. InVision (ISCEV) standard ERG protocol. Inaa light-adaptedlight-adapted eye, a flicker ERG tests aeye, a flicker ERG tests aresponse arising from theresponse arising from the conescones. The. Theflicker ERG has also been shown to beflicker ERG has also been shown to beuseful in patients with diabetic retinopathy.useful in patients with diabetic retinopathy. 20. ff ERGff ERG 21. mfERGmfERG The mfERG is an important clinical toolThe mfERG is an important clinical toolboth because it can detectboth because it can detect localizedlocalizedabnormalities and because it provides aabnormalities and because it provides ameans to assessmeans to assess central and peripheralcentral and peripheralfunction separatelyfunction separately.. 22. 61 or 103 focal ERG responses can be61 or 103 focal ERG responses can berecordedrecorded from the cone-driven retina. withfrom the cone-driven retina. withcentral elements that are much smallercentral elements that are much smallerthan peripheral elements because thethan peripheral elements because thereceptive fields are larger in the periphery.receptive fields are larger in the periphery.The tested area typically spans 20-30The tested area typically spans 20-30degrees to each side of the foveadegrees to each side of the fovea 23. During the test, approximately half of theDuring the test, approximately half of theelements are illuminated at any givenelements are illuminated at any giventime,time, Because the electrodes are placed on theBecause the electrodes are placed on thecornea and offercornea and offer no spatial resolutionno spatial resolution bybythemselves, the response generated is notthemselves, the response generated is nottruly a series of individual responsetruly a series of individual responseelements but rather the result ofelements but rather the result ofmathematical calculationmathematical calculation 24. N1: off bipolarP1: on bipolarN2: on bipolar recovery 25. The results of the mfERG test can beThe results of the mfERG test can bedisplayed in several waysdisplayed in several ways.. 26. Summation of all the responses to theSummation of all the responses to themfERG generates a waveform similar tomfERG generates a waveform similar tothat of the ffERG maximum responsethat of the ffERG maximum responsethough represent very differentthough represent very differentmeasurements. The full-field ERG showsmeasurements. The full-field ERG showsthe direct response tothe direct response to changes inchanges inluminance,luminance, whereas the multifocal ERG iswhereas the multifocal ERG isa mathematically derived representation ofa mathematically derived representation ofthe response tothe response to changes in contrastchanges in contrast 27. pERGpERG The pattern ERG provides a useful measure ofThe pattern ERG provides a useful measure ofmacular functionmacular function and generalized bipolar celland generalized bipolar cellfunction.function. The most common stimulus is aThe most common stimulus is a checkerboardcheckerboardstimulus composed of white and black squaresstimulus composed of white and black squares The test measuresThe test measures response to contrastresponse to contrastchangeschanges, not luminance changes, so the overall, not luminance changes, so the overallluminance of the stimulator must remainluminance of the stimulator must remainconstant, spatially regular, fully symmetrical andconstant, spatially regular, fully symmetrical andcentered on the foveacentered on the fovea 28. alternates with a regular frequency and aconstant luminance 29. The normal pattern electroretinogram : N35, a small negativecomponent with a peak time occurring around 35 ms; P50, aprominent positive wave emerging around 50 ms and N95, a widenegative wave around 95 ms 30. thethe P50P50 component was shown to becomponent was shown to bealtered in all patients withaltered in all patients with retinalretinal andandmacular diseasesmacular diseases. On the other hand, the. On the other hand, theN95N95 component was abnormal in 81% ofcomponent was abnormal in 81% ofpatients with diseases of thepatients with diseases of the optic nerveoptic nervewhile the P50 component remainedwhile the P50 component remainednormal.normal. 31. Pattern electroretinograms(PERGs) elicited by 4 Hz (eightreversals per second) from a37-year-old white female patientwith pseudotumor cerebri. Theupper tracing is a normal PERGfrom the right eye. Note that N2(N95) is larger than P1 (P50).The PERG in the lower tracing,from the affected left eye, isseverely reduced. PERGs wererecorded using 64 samples andan outer canthal reference. 32. APPLICATIONSAPPLICATIONS Toxicity and vitamin deficiency;Toxicity and vitamin deficiency; Numerous toxic compounds diminish retinal function andNumerous toxic compounds diminish retinal function andcan be assessed and monitored with ERG testing. Forcan be assessed and monitored with ERG testing. Forexample,example, vigabatrinvigabatrin, an anti-epileptic or HCN, an anti-epileptic or HCN Vitamin A deficiencyVitamin A deficiency can be suggested by ancan be suggested by anundetectable scotopic ERG responseundetectable scotopic ERG response, even with, even withincreased luminance, in conjunction with minimallyincreased luminance, in conjunction with minimallyreduced 30-Hz flicker and photopic responses. Visualreduced 30-Hz flicker and photopic responses. Visualfunction can be largely restored within a week offunction can be largely restored within a week oftreatment.treatment. 33. congenital stationary night blindnesscongenital stationary night blindness(CSNB) is an inherited condition affecting(CSNB) is an inherited condition affectingrod cells, thereby preventing night visionrod cells, thereby preventing night vision(AD, AR, XL)(AD, AR, XL) Some patients show only rod-specific scotopicSome patients show only rod-specific scotopicreduction, while many others experience anreduction, while many others experience anelectronegative b wave on the maximumelectronegative b wave on the maximumscotopic test as well. The transient photopic b-scotopic test as well. The transient photopic b-wave is delayed in some patientswave is delayed in some patients 34. Retinitis pigmentosa (RP)Retinitis pigmentosa (RP) Rod-cone degenerationsRod-cone degenerations Patients withPatients with early-stageearly-stage RP tend to showRP tend to showgreatly reduced scotopic rod response andgreatly reduced scotopic rod response andsome decrease in maximum responsesome decrease in maximum responseamplitude, corresponding to the early loss of rodamplitude, corresponding to the early loss of rodphotoreceptors. As the diseasesphotoreceptors. As the diseases progressesprogresses, the, themaximal ERG, 30-Hz flicker, and photopicmaximal ERG, 30-Hz flicker, and photopicresponses also steadily diminish as cone cellsresponses also steadily diminish as cone cellsdie. An implicit time delay is often seen, whichdie. An implicit time delay is often seen, whichdemonstrates generalized dysfunctiondemonstrates generalized dysfunction.. 35. Retinitis pigmentosa is aRetinitis pigmentosa is a heterogeneousheterogeneousdisease that has been associated with mutationsdisease that has been associated with mutationsin 34 different genes. The specific gene affectedin 34 different genes. The specific gene affectedin a given patient dictates the inheritancein a given patient dictates the inheritancepattern.pattern. Autosomal recessiveAutosomal recessive cases account forcases account forapproximately 60 percent of total RP cases andapproximately 60 percent of total RP cases andhave been associated with mutations in 17have been associated with mutations in 17different genes.different genes. Autosomal dominantAutosomal dominant inheritanceinheritancedefines approximately 15 to 35 percent of casesdefines approximately 15 to 35 percent of casesand is associated with 15 known mutations. Theand is associated with 15 known mutations. TheX-linkedX-linked form of RP is associated with just threeform of RP is associated with just threegenes and accounts for approximately 5 to 18genes and accounts for approximately 5 to 18percent of total casespercent of total cases.. 36. TheThe full-field ERGfull-field ERG is an essential clinicalis an essential clinicaltool fortool for diagnosing and monitoringdiagnosing and monitoring retinitisretinitispigmentosa. Thepigmentosa. The 30 Hz flicker30 Hz flicker amplitudeamplitudecan be used tocan be used to estimate the length of timeestimate the length of timethat a patient will retain useful visionthat a patient will retain useful vision,,based on an assumedbased on an assumed lossloss ofofapproximatelyapproximately 10% each year10% each year with nowith notreatmenttreatment ffERG is also important for geneticffERG is also important for geneticcounselingcounseling 37. Age-related macular degeneration (AMD)Age-related macular degeneration (AMD)Because it is contained within theBecause it is contained within themacula,macula, thethe ffERGffERG often showsoften shows normalnormaloverall function. There may a slight drop inoverall function. There may a slight drop incone response amplitude, but the implicitcone response amplitude, but the implicittime, which typically signals generalizedtime, which typically signals generalizedfunction, is normal. However, thefunction, is normal. However, the pERGpERG,,which measures macular funciton, iswhich measures macular funciton, ismarkedly reducedmarkedly reduced.. 38. VariabilityVariability ERGs measure the response to light, so theERGs measure the response to light, so thepupil should be maximally dilatedpupil should be maximally dilated every time anevery time anERG is performed; changes in pupil dilation canERG is performed; changes in pupil dilation canreduce the potential.reduce the potential. SystemicSystemic blood pressureblood pressure and local blood flowand local blood flowcan affect ERG amplitude.can affect ERG amplitude. Patients also experience aPatients also experience a diurnal changediurnal change ininsignal amplitude as a result of circadiansignal amplitude as a result of circadianphysiological changes including blood pressurephysiological changes including blood pressureand rod outer-segment disc sheddingand rod outer-segment disc shedding 39. VariabilityVariability CertainCertain anestheticsanesthetics can affect the b-wavecan affect the b-waveamplitude, so they should be noted asamplitude, so they should be noted aswell.well. Ocular movementOcular movement can generatecan generateinterference in ffERG testing and stronglyinterference in ffERG testing and stronglyaffects the results of spatially specific testsaffects the results of spatially specific testssuch as the mfERG, so the patientssuch as the mfERG, so the patientsfixation should be closely monitored by thefixation should be closely monitored by theclinician.clinician. 40. ELECTRO-ELECTRO-OCULOGRAPHYOCULOGRAPHY 41. DEFINITIONDEFINITION The clinical electro-oculogram is anThe clinical electro-oculogram is anelectrophysiological test of function of theelectrophysiological test of function of theouter retina and retinal pigment epitheliumouter retina and retinal pigment epitheliumin which the change in the electrical potentialin which the change in the electrical potentialbetween the cornea and the fundus is recordedbetween the cornea and the fundus is recordedduring successive periods ofduring successive periods of dark and lightdark and lightadaptation.adaptation. 42. HISTORYHISTORY Emil du Bois-Reymond (1848) observed that theEmil du Bois-Reymond (1848) observed that thecornea of the eye is electrically positive relative to thecornea of the eye is electrically positive relative to theback of the eye.back of the eye. Elwin Marg named the electrooculogram in 1951 andElwin Marg named the electrooculogram in 1951 andGeoffrey Arden (Arden et al. 1962) developed theGeoffrey Arden (Arden et al. 1962) developed thefirst clinical applicationfirst clinical application 43. The eye has a standing electrical potential between frontThe eye has a standing electrical potential between frontand back, sometimes called theand back, sometimes called the corneo-fundalcorneo-fundalpotentialpotential. The potential is. The potential is mainly derived from the retinalmainly derived from the retinalpigment epithelium (RPE)pigment epithelium (RPE), and it changes in response to, and it changes in response toretinal illuminationretinal illumination The potential decreases for 810 min in darkness.The potential decreases for 810 min in darkness.Subsequent retinal illumination causes an initial fall in theSubsequent retinal illumination causes an initial fall in thestanding potential over 6075 s (the fast oscillationstanding potential over 6075 s (the fast oscillation(FO)), followed by a slow rise for 714 min (the light(FO)), followed by a slow rise for 714 min (the lightresponse). These phenomena arise from ionresponse). These phenomena arise from ionpermeability changes across the basal RPE membrane.permeability changes across the basal RPE membrane. 44. The clinical electro-oculogram (EOG)The clinical electro-oculogram (EOG)makes an indirect measurement of themakes an indirect measurement of theminimum amplitude of the standingminimum amplitude of the standingpotential in the dark and then again at itspotential in the dark and then again at itspeak after the light rise. This is usuallypeak after the light rise. This is usuallyexpressed as aexpressed as a ratio of light peak toratio of light peak todark troughdark trough and referred to as theand referred to as the ArdenArdenratioratio.. 45. Measurement of the clinical EOGMeasurement of the clinical EOG The calibration of the signal may be achieved byThe calibration of the signal may be achieved byhaving the patient lookhaving the patient look consecutively at two differentconsecutively at two differentfixation points located at known angle apartfixation points located at known angle apart andandrecording the concomitant EOGs .recording the concomitant EOGs . By attaching skin electrodes on both sides of an eyeBy attaching skin electrodes on both sides of an eyethe potential can be measured by having the subjectthe potential can be measured by having the subjectmove his or her eyes horizontally a set distancemove his or her eyes horizontally a set distance .. 46. The standard methodThe standard method After training the patient in the eyeAfter training the patient in the eyemovements, the lights are turned off.movements, the lights are turned off. About every minute a sample of eyeAbout every minute a sample of eyemovement is taken as the patient is asked tomovement is taken as the patient is asked tolook back and forth between the two lights .look back and forth between the two lights . After 15 minutes the lights are turned on andAfter 15 minutes the lights are turned on andthe patient is again asked about once a minutethe patient is again asked about once a minuteto move his or her eyes back and forth forto move his or her eyes back and forth forabout 10 seconds.about 10 seconds. 47. The standard methodThe standard method Typically the voltage becomes a little smaller in theTypically the voltage becomes a little smaller in thedark reaching its lowest potential after about 8-12dark reaching its lowest potential after about 8-12minutes, the so-called minutes, the so-called dark troughdark trough.. When the lights are turned on the potential rises, theWhen the lights are turned on the potential rises, thelight rise, reaching its peak in about 10 minutes.light rise, reaching its peak in about 10 minutes. When the size of the "When the size of the "light peaklight peak" is compared to the" is compared to the"dark trough" the relative size should be about"dark trough" the relative size should be about 2:1 or2:1 orgreater .greater . AA light/dark ratio of less than about 1.7 islight/dark ratio of less than about 1.7 isconsidered abnormalconsidered abnormal.. 48. APPLICATIONSAPPLICATIONS The light response is affected in:The light response is affected in:- diffuse disorders of the RPE and the photoreceptor- diffuse disorders of the RPE and the photoreceptorlayer of the retina including some characterized by rodlayer of the retina including some characterized by roddysfunctiondysfunction- chorio-retinal atrophic and inflammatory diseases- chorio-retinal atrophic and inflammatory diseases In most of these there is correlation with theIn most of these there is correlation with theelectroretinogram (ERG), except notably in the case ofelectroretinogram (ERG), except notably in the case ofBests vitelliform maculopathyBests vitelliform maculopathy, in which the clinical, in which the clinicalEOG is usually highly abnormal in the presence of aEOG is usually highly abnormal in the presence of anormal ERGnormal ERG May be an early indicatorMay be an early indicator of Chloroquine toxicityof Chloroquine toxicity 49. BEST DiseaseBEST Disease 50. BEST DiseaseBEST Disease a slowly progressivea slowly progressive macular dystrophymacular dystrophywith onset generally inwith onset generally in childhoodchildhood andandsometimes in later teenage yearssometimes in later teenage years Sight loss can be variable but, like otherSight loss can be variable but, like othermacular problems, Bests disease threatensmacular problems, Bests disease threatenscentral vision in one or both eyes.central vision in one or both eyes. WithinWithin 5 identifiable stages5 identifiable stages, examination of, examination ofthe eye discloses a distinct progression. At firstthe eye discloses a distinct progression. At firstand second stages, there may be little or noand second stages, there may be little or noeffect on sight.effect on sight. 51. BEST DiseaseBEST Disease Initially a recording of eye movements and eye positionInitially a recording of eye movements and eye positionidentifies abnormal electrical potential.identifies abnormal electrical potential. At the second stage (usually between 10-25 years of age),At the second stage (usually between 10-25 years of age),typical yellow spots, sometimes accompanied by materialtypical yellow spots, sometimes accompanied by materialleaking into a space by the retina, can be observed; anleaking into a space by the retina, can be observed; anobservation called "egg-yolk" lesion.observation called "egg-yolk" lesion. When part of the lesion becomes absorbed this is identified asWhen part of the lesion becomes absorbed this is identified asstage three.stage three. At the fourth stage, when the "egg-yolk" breaks up, in aAt the fourth stage, when the "egg-yolk" breaks up, in aprocess referred to as "scrambled-egg", sight will probably beprocess referred to as "scrambled-egg", sight will probably beaffected.affected. The fifth and final stage is when the condition causes the mostThe fifth and final stage is when the condition causes the mostsevere sight loss.severe sight loss. 52. Other diseasesOther diseases The curves of the EOG of theThe curves of the EOG of the depresseddepressedpatients have lower amplitude.patients have lower amplitude. The normalised mean EOG amplitudesThe normalised mean EOG amplitudesobtained from a group ofobtained from a group of amblyopicamblyopic eyes wereeyes weresignificantly lower that the normalised meansignificantly lower that the normalised meanamplitudes from the fellow eyes at all timeamplitudes from the fellow eyes at all timepoints during the EOG recordingpoints during the EOG recording ed Amplitude of EOG seen with use of :ed Amplitude of EOG seen with use of :Mannitol,Acetazolamide,BicarbonateMannitol,Acetazolamide,Bicarbonate 53. Visual evoked potentialVisual evoked potential Gross electrical signal generated at visual cortexGross electrical signal generated at visual cortexin response to visual stimuliin response to visual stimuli Impulses carried to visual cortex via visualImpulses carried to visual cortex via visualpathwaypathway Recorded by EEGRecorded by EEG It is the only objective technique to assessIt is the only objective technique to assessclinical and functional state of visual syst.beyondclinical and functional state of visual syst.beyondretinal ganglion cells.retinal ganglion cells. 54. Types of VEPTypes of VEP1.1. Pattern VEPPattern VEP (checker-board(checker-boardpatterns on TV monitor)patterns on TV monitor)2.2. Flash VEPFlash VEP (diffuse flash light for(diffuse flash light foruncooperative subjects)uncooperative subjects) 55. VEPVEP Un-dilated pupils. Sit 1 meter from monitorUn-dilated pupils. Sit 1 meter from monitor Electrodes in midline at forehead, vertex &Electrodes in midline at forehead, vertex &occipital lobesoccipital lobes 2-3 different checker sizes are shown2-3 different checker sizes are shown Recording is doneRecording is done 56. VEPVEPNormal waveformNormal waveform Pattern VEPPattern VEP has initial ve (has initial ve (NN11))+ve(+ve(PP11))second ve (second ve (NN22) wave) wave Positive wave Positive wave 70 100 ms70 100 ms Negative wave Negative wave 100 130 ms100 130 ms Positive wave -Positive wave - 150 200 ms150 200 ms Flash VEPFlash VEP is complex. 2 positive & 2is complex. 2 positive & 2negatives.negatives. 57. VEP IndicationsVEP Indicationsa)a) Un-explained visual lossUn-explained visual lossb)b) Optic neuritisOptic neuritisc)c) Multiple sclerosisMultiple sclerosisd)d) Compressive ON lesionsCompressive ON lesionse)e) Cortical blindnessCortical blindnessf)f) AmblyopiaAmblyopiag)g) GlaucomaGlaucoma 58. THANK YOU