ERG and VEP Flashcards
What kind of ERG would you use for plaquenil retinopathy and what would you see? What kind of VF could you use?
Plaquenil retinopathy looks for damage of outer retina
Use mfERG
ERG would look like Mt St Helens
Could also use 10-2 visual field
What kind of ERG would you use for Glaucoma? What’s the most common tool for seeing structure abnormalities in glaucoma?
Glaucoma affects ganglion cells. Use pERG.
Commonly use OCT for structure
What else can you visualize with ERG?
Glaucoma
Plaquenil retinopathy
Siderosis Bulbi
Genetic defects in children
Differentiate RP and CSNB
RP has flatter ERG curveWhat diseases would you expect to see only a sandcastle tiny peak in ERG (with periphery black)
Tiny sandcastle is caused by being mostly blind. Maybe some tunnel vision
Glaucoma, RP, CSNB, other genetic disorders causing blindness
What diseases would you expect to see lopped off Mt St Helens
Macula affected but periphery may still work
Plaquenil retinopathy
ARMD and Stargardt’s
Macular hole
What might you notice on a gross level in a child with Leber’s Congenital amaurosis?
Gaze disorder
No response to Teller Cards
Stages of Leber’s Congenital amaurosis?
Mild: Looks pretty normal
Moderate: Scleral window over macula
Severe: Widening of window and buildup of pigment around it - might look like RP
What tests could you use on LCA? (2)
ERG: Will be flatline at early age
Fluoroscein: Salt and pepper fundus
What do visually evoked potentials (VEPs) measure?
Objective VAs
How cortex responds to visual stimuli
What structures do VEPs measure?
Activity of cells in visual cortex
Usually V1
2/3 of cells for fovea
What stimuli do you use for VEPs?
Anything that changes Pattern Luminance Color Most common reverse phase checkerboard Decreases in size/VAs
Why would you use a phase reversing checkerboard to get VEPs
Want to stimulate simple cells
Can’t be held steady or not as much stimulation
Flickers
VEP vs ERG. Tell me what would happen with a full retinal stimulus, peripheral stimulus and foveal stimulus
Full retinal: Equal VEP and ERG
Foveal: VEP same as full retinal, ERG is reduced
Again, VEP focuses on V1 which is 2/3 foveal
Peripheral: VEP almost flatlines ERG is same as foveal
In mV, what’s the amplitude of brain noise?
60mV
What voltage does EOG measure?
6mV
What voltage does ERG measure?
1mV
How do you separate background noise in VEP?
To separate background noise, consider that VEP signals take 80ms to get through optic nerve to cortex. Filter out noise of EEG. Zeroes it out to allow you to see VEP
Stimuli for flash (AKA transient) VEP?
Alternating Black an white square separated by 250ms. Luminance is constant but pattern changes
Who would you use a flash (AKA transient) VEP on?
Babies that may not respond to visual stimuli but do respond to auditory stimuli
See of optic nerve works
What are you looking when analyzing results of a VEP?
Amplitude and latency
What stimulus does a steady state (AKA Flicker) VEP use? At what CFF?
Phase reversing checkerboard flashing at 20 Hz
Similar to pERG
Which is more accurate, the transient/flash VEP or the flicker/steady state VEP?
Flicker/Steady state VEP
What’s the advantage of multifocal VEP?
Multifocal VEP can measure threshold contrast and also looks at multiple retinal loci
Compare to mfERG which also looks at multiple points on the retina
How would you find threshold contrast with multifocal VEP?
Start at high contrast and go lower. Plot on graph with VEP amplitude on y and contrast on x. Extrapolate your resultant line down to the X intercept
What can you do to enhance mfVEP?
Conscious attention
What does wave that results from VEP look like?
3 dips and 3 peaks starting with a dip.
What can the VEP assess (5)
Foveal patency
Why is VEP best for Foveal patency?
VEP looks at visual cortex signals, most of which are from the fovea (2/3)
What can cause decrease in foveal patency
Cortical blindness, Cataracts, during surgery
How would you set up a patient to be tested for Optic nerve conduction with a VEP
Put patient in Ganzfeld with red bowl. Increased latency = demyelination
With MS, long latency even during remission
How would you be able to tell that there was poor conduction in the optic nerve using a VEP?
Long latency
What visual field defect would you notice in Leber’s optic neuropathy?
Size of normal scotoma will be enlarged
What does acute Leber’s look like on the optic nerve?
Papilledema
What does chronic leber’s optic neruopathy look like?
Pallor
According to Kollner’s rule, what color defect would you get in Leber’s optic neuropathy?
Red/Green
Same as MS because ON affected
What would you analyze on VEP graph to determine the refractive error
Amplitude
Why would you use VEP to assess refractive error in babies?
See if glasses would help infant
When do babies have 20/20 VEP potential?
6 months
What’s the problem with measuring VEP in babies?
OVERESTIMATES their potential
How much greater is VEP due to binocular summation?
1.4x
When would binocular VEP be greater or less than what you’d expect?
Less = Poor binocularity = amblyopia More = abnormal crossing at chiasm = albinism
How would you differentiate amblyopia and a retinal defect?
Retinal defect would show abnormal ERGs and VEPs
Amblyopia would show normal ERGs but abnormal VEPs
What stream does VEP predominantly look at? Why would this be a problem?
Parvo. Might miss magno stuff - like glaucoma.
