VEP for the 21st Century

VEP For The 21st CenturyJody Abrams, MD

Sarasota Retina Institute

Disclosures

I do neuro-ophthalmology so no financial

disclosures

I do refuse to wear a bowtie

We do own one of the VEP machines

VEP For The 21st Century

The SRI Update course baby

VEP For The 21st Century

VEP: visually evoked potential, visually evoked

response, and visually evoked cortical potential

Electrical impulse from the eye to the brain

Part of an EEG

VEP For The 21st Century

VEP For The 21st Century

Functional integrity of entire visual pathway

Anterior Segment to Visual Cortex

VEP For The 21st Century First noticed during strobe lights with early EEGs in

the 30s

Computers were able to extract the visual potentials with signal averaging

Similar to anti-radar jamming programs in the 50s

Saves defined time period of activity and averages out the randomness

VEP For The 21st Century

Electrical signal for VEP is 1-20 microvolts

Computer’s data acquisition is synchronized to the timing of the visual stimulus

Apply signal averaging to repeated stimuli and

the wave form is captured

VEP For The 21st Century

Pattern reversal stimulation is preferred testing

stimuli

Black and white checker board alternates

Light output remains the same

VEP response is from detection of edges between

the white and black areas

VEP For The 21st Century

First negative peak is N75

First positive peak is P100

Second negative peak is

N135

VEP For The 21st Century

Amplitude is amount of

energy reaching the

cortex

Difference between N75

and P100

Normal is around 6 microvolts for 32x32 board

VEP For The 21st Century

Amplitude gives how much information is making

it to the occipital lobe

Increase often can indicate better discrimination

Refraction can be a big issue with this

VEP For The 21st Century

Latency is the time it takes to get the information

back to the occipital lobe

P100 is peak of the information getting to the

visual cortex

Average is 100 ms (97-117)

VEP For The 21st Century

Latncy is increased by impedance in conduction

Less variation then amplitude

VEP For The 21st Century

Most common pattern is checkered board or

bars

Best response in normal patients at 32x32

pattern size

Adjust for level of vision

VEP For The 21st Century

Contrast is adjusted for cell bias

High contrast for parvocellular

Low contrast for magnocellular

VEP For The 21st Century

Parvocellular cells most

abundant

Sensitive to color

Help with discriminating fine

detail

VEP For The 21st Century

Magnocellular cells

Coarse vision

Motion

More sensitive with low contrast

Thought to be damaged in

early glaucoma

VEP For The 21st Century

Flash VEP good for extreme vision loss or if not

able to focus on screen

Look at N2 (90 ms) and P2 peaks (120ms)

VEP For The 21st Century

Machines used to be

complicated

Mostly reserved to

universities

VEP For The 21st Century

Computer advancements

More compact system

Easier tech work

Interpretation easier

VEP For The 21st Century

Now in ophthalmology offices, optometry

offices, and neurology clinics

Use has exploded

Need to at least know what it means

VEP For The 21st Century

VEP is a tool

Does not give the diagnosis

A “semi” objective way

to track change

VEP For The 21st Century

VEP ignores the appearance

It looks at how the system runs

VEP For The 21st Century

Amblyopia

Glaucoma

Traumatic Brain Injury

Optic Neuritis/MS

Other causes of optic nerve dysfunction

Functional visual loss

Dense cataracts

VEP For The 21st Century

55 y/o BF

Family hx of glaucoma

IOP 21/19

Corneal thickness 555/542

VEP For The 21st Century

Angles open

C/D 0.7 ou

VEP For The 21st Century

HVF normal OU

SD-RNFL 92 and 88

Would you treat?

VEP For The 21st Century 34 y/o obese WF

Headaches

Sent with dx of PTC

On Diamox 500 bid

Denies visual complaints

VEP For The 21st Century

VA 20/25 ou

Pupils no APD, no light/near disassociation, brisk

VEP For The 21st Century

Is it time to rush to OR for a nerve sheath

fenestration or VP shunt?

Can the Diamox be increased and watch

closely?

VEP For The 21st Century 32 WF

1 s/p delivery with eclampsia

Now has LP vision ou

Pupils brisk, no APD, no LND

CF unreliable

VEP For The 21st Century

-9 myopia ou

Tilted Optic nerves

OCTs show thinning but difficult scan secondary

to optic nerve anatomy

VEP For The 21st Century

Is this a real problem?

Refuses MRI

OB/GYN feels is faking it to get attention

Posterior reversible encephalopathy syndrome

VEP For The 21st Century

89 yo WM

Sent over for abnormal VF and VEP

Pt has not noticed visual change

Original fields appeared to have Left

homonymous hemianopia

This lead to MRI

which was read as

normal

A VEP was done

VEP For The 21st Century

Our Exam

20/25 ou

Pupils no APD, no L/N, brisk

Fundus showed Dry ARMD

RNFL

OD 103

OS 107

VEP does not give all the answers

Make sure getting good data

If it does not make sense with all the other

information repeat the test

CPT code 95930