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38 Cards in this Set
- Front
- Back
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Transient VEP |
pattern reversal VEP; Peaks occur at constant latency after stimulus; more clinically relevant |
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VEP diseases |
Multiple sclerosis, Optic Neuritis |
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Visual acuity associated with VEP abnormalities |
20/200 or greater
Increased P100 latency primarily
Decreased amplitude |
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Visual acuity: Which # represents the diseased eye? 1st? 2nd? |
1st |
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Explain a visual acuity of 20/200 |
Nml vision pt can read chart at 100ft, but decreased vision pt must stand at 20 ft |
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Explain a visual acuity of > 20/20 |
Refractory error; pt can't see |
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Two types of VEP tests |
FLASH VEP/ LED Gogggles= Gross test function; non-localizing; can't tell where on visual pathway affected; used w/ babies ot pt unable to look at screen
Full field pattern reversal= optic nerve/ pre-chiasmal function test; This will not be on exam and will not be an answer |
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Left eye stimulation: Where is the response maxiamal to full field PR VEP?
LO, MO, RO? |
MO |
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Visual angle |
Perceived size impacted by distance |
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Visual angle to stimulate central vision/ foveal vision |
24-32 minutes of arc |
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Why is stimulating above 32 min of arc not recommended? |
Big/insensitive # everyone would test nml; same for <24 everyone would test abn |
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EQUATION: Visual angle in minutes of arc |
(3438 X check width) / distance from screen |
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What is the recommended fixation point for full field PR VEP |
Center of screen |
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ACNS guideline: Stimulator type |
Black and white checks |
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ACNS guideline: Constrast |
high; >50% |
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ACNS guideline: Stimulation or pattern reversal rate |
1.9-4/ sec |
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When might you change stim parameters |
Never; except for analysis time when no response is seen. 250msec to 500msec |
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Luminance vs contrast |
Luminance= amount of light coming in
Contrast= difference in luminance of the black check to the white check |
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Effect on VEP when luminance is decereased |
Increases latency
decrease amplitude |
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ACNS guideline: Bandpass |
1-100Hz |
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ACNS guideline: Filter Rolloff Slopes |
Not to exceed: 12dB/ octave low frequencies 24dB/octave high frequencies |
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ACNS guideline: Analysis time |
250 msec: up to 500 msec if signal is absent |
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Queen's square placement |
MF: 12cm above nasion MO: 5cm above inion LO: 5cm left of MO RO: 5cm right of MO A1: left ear lobe Ground: Cz |
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VEP montages (4) |
LO-MF MO-MF RO-MF MF-A1 |
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Other names for left and right eyes |
Oculus sinister (L) Oculus Dexter (R) |
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Clinically useful measurements for VEP |
P100 latency at MO
amplitude of P100 at all 3 occipital sites
>4ms inter-ocular latency difference= abn |
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Homonymous Hemianopsia |
Lesion behind chiasm (retro-chiasm); stroke; most often in occipital lobe |
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Age at which children VEPs have adult morphology |
6 months |
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Most important subject variable affecting VEP |
Age |
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What effect does anesthesia have on VEPs |
None |
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Lateral geniculate body |
Associated w/ VEP; found inside thalamus; processes visual info |
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Optic Neuritis |
Inflammation of optic nerve; uni/bilateral; increased P100 latency; Decreased P100 amplitude |
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Uhtoff's Phenomenon/Sign |
Worsening of neurologic symptoms in MS when body gets hot/oveheats; visual blurring, paresthesia, numbness |
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Lhermitte's Sign |
Electrical sensation that runs down back from involvement of posterior columns when bending neck; Classical sign in MS. |
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Friedrichs Ataxia/ VEP |
VEPs delayed in latency |
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How to calculate if noise in channel is 60 Hz |
0.06 X analysis= # of peaks in window
interpeak: 16.6ms |
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P300 |
Cognitive Evoked potential
Odd-Ball paradigm
High and low frequency auditory tones are presented
C3, CZ, C4, P3, PZ, P4
Abn in Alzheimer's/ pt w/ cognitive delays |
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Contingent Negative Variation |
Expectancy Wave
click followed by flash or absent of flash
response occurs if flash comes or not
test of discrimination |
