Multifocal VEP: insights into Multifocal VEP: insights into the optic neuropathiesthe optic neuropathies

Save Sight Institute Save Sight Institute

University of SydneyUniversity of Sydney

MFVEP- unique diagnostic MFVEP- unique diagnostic testtest

Distinct from conventional VEPDistinct from conventional VEP Topographic informationTopographic information Finer and more complete samplingFiner and more complete sampling

More than a perimetric testMore than a perimetric test AmplitudeAmplitude LatencyLatency

Insights into pathophysiology of optic Insights into pathophysiology of optic pathway diseasespathway diseases

Compare FFVEP & MFVEPCompare FFVEP & MFVEP

50 degrees

Multifocal VEP

“Full-field” VEP

FFVEP & MFVEPFFVEP & MFVEP

Preservation of peripheral mfVEP

Absent

Normal eye Optic Neuritis

FF VEP

MF VEP

FFVEP & MFVEPFFVEP & MFVEPNormal Traumatic optic neuropathy

Preserved ff VEP

mfVEP – significant losses, central inferior signal preserved

What is Multifocal VEP and how What is Multifocal VEP and how it works? it works?

Multifocal VEP stimulation and Multifocal VEP stimulation and recordingrecording

Striate cortex Visual field

L Calcarine fissure R

Recording channels

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+

+ -

_

+

Extraction of mfVEP by cross-Extraction of mfVEP by cross-correlationcorrelation

Clinical application of multifocal VEP Clinical application of multifocal VEP in glaucomain glaucoma

Why pursue objective Why pursue objective testing ?testing ?

Limitations of subjective Limitations of subjective teststests High level of co-operation High level of co-operation

requiredrequired Variable performanceVariable performance Learning curveLearning curve Patient complaints – stressfulPatient complaints – stressful Late detection of Late detection of

glaucomatous damage glaucomatous damage

Using achromatic Using achromatic stimulation various types stimulation various types

of scotoma can be of scotoma can be identifiedidentified

sensitivity of the technique:sensitivity of the technique:

in in early glaucoma 90-95% early glaucoma 90-95% in moderate to advance in moderate to advance

glaucoma-100%glaucoma-100%

(at specificity of 95%)(at specificity of 95%)

Example of glacoma patient with unreliable Example of glacoma patient with unreliable subjective visual field and normal optic disc-subjective visual field and normal optic disc-

mfVEP normalmfVEP normal

Sparse pattern-onset Sparse pattern-onset

stimulationstimulation Bright yellow backgroundBright yellow background Blue checks Blue checks

To improve mfVEP sensitivity in early To improve mfVEP sensitivity in early glaucoma Blue-on-Yellow Stimulation was glaucoma Blue-on-Yellow Stimulation was

introducedintroduced

It demonstrated:It demonstrated:100% sensitivity in early perimetric glaucoma 100% sensitivity in early perimetric glaucoma 95% specificity95% specificityLarger defects compared to black-and-white Larger defects compared to black-and-white mfVEP for the same eyes, especially in very mfVEP for the same eyes, especially in very early defectsearly defects

Blue-on-Yellow mfVEP was then applied Blue-on-Yellow mfVEP was then applied to pre-perimetric glaucoma to pre-perimetric glaucoma

14 out of 30 patients with pre-perimetric 14 out of 30 patients with pre-perimetric glaucoma had mfVEP defectsglaucoma had mfVEP defects

In all 14 cases, location of mfVEP defects In all 14 cases, location of mfVEP defects

corresponded topographicallycorresponded topographically with the with the worst affected rimworst affected rim

Example 1 of Example 1 of pre-perimetricpre-perimetric glaucoma glaucoma

Example 2 of Example 2 of pre-perimetricpre-perimetric glaucoma glaucoma

New stimulation technique New stimulation technique for simultaneous for simultaneous

BINOCULAR recording BINOCULAR recording using Virtual Reality using Virtual Reality

GogglesGoggles

MfVEP can be successfully used to MfVEP can be successfully used to detect visual field defect detect visual field defect

MfVEP can identifies defects in nearly MfVEP can identifies defects in nearly 50% patients with pre-perimetric 50% patients with pre-perimetric glaucoma which corresponded to glaucoma which corresponded to structural changes structural changes

ConclusionConclusion

R

Glaucoma subject

-Right eye scotoma

-Left eye normal VF

L

Utility of multifocal VEP in Utility of multifocal VEP in

optic neuritis.optic neuritis.

1. Multi-focal VEP amplitude as a marker of extent and evolution of inflammation in acute stage of ON

10 days-amplitude extinguished across whole field except temporal paracentral area

20 days- amplitude extinguished in the rest of the field, but begins to recover at some peripheral locations

1 month-significant recovery of amplitude in areas of visual field initially affected

2 month-amplitude still reduced in temporal paracentral area

3 month-almost complete amplitude recovery, small relative depression remains in temporal paracentral area

2. Multi-focal VEP amplitude as a marker of axonal

recovery/degeneration in post-acute stage of ON

Patient JL-”not-MS”

Monitoring axonal recovery-1Monitoring axonal recovery-1

1 month after ONASI=196

3 monthASI=140

6 monthASI=78

12 monthASI=39

1 month

3 month

6 month

12 month

MC-”MS”

Monitoring axonal degenerationMonitoring axonal degeneration

Example of gradual amplitude loss

3. Using multi-focal VEP to determine 3. Using multi-focal VEP to determine degree and topography of demyelinationdegree and topography of demyelination

Latency analysis of individual Latency analysis of individual segmentssegments

Non-affected eye

Affected eye

Detecting demyelination

Non-affected eye

Affected eye

complete amplitude recovery but significant complete amplitude recovery but significant delaydelay

1 m post-ON

Latency delay

4. Using multi-focal VEP to 4. Using multi-focal VEP to monitor remyelinationmonitor remyelination

VEP traces Amplitude Ampl asymmetry Latency Latency asymmetry

Example of good latency recoveryExample of good latency recovery

ConclusionConclusionThe mfVEP may be used to track The mfVEP may be used to track recovery of function in optic neuritisrecovery of function in optic neuritis

The rate and extent of functional recovery of The rate and extent of functional recovery of both amplitude and latency may have both amplitude and latency may have significance in terms of underlying significance in terms of underlying pathological processes, and ultimate pathological processes, and ultimate prognosis for conversion to MSprognosis for conversion to MS

It may be possible to use the mfVEP as a It may be possible to use the mfVEP as a monitor for remyelination in patients monitor for remyelination in patients undergoing treatment for early diseaseundergoing treatment for early disease