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Visual Evoked Potentials
12
March 2003
VEP diagram
Reference Values:
|
P100 |
Female |
Male |
|
<60 |
115 |
120 |
|
>60 |
120 |
125 |
<10ms difference between sides.
Smaller checks and higher contrast
increase size of P100
Montage
|
Channel 1 |
O2 – reference |
|
Channel 2 |
OZ – reference |
|
Channel 3 |
O1 – reference |
|
Channel 4# |
LT – reference |
|
Channel 5# |
RT – reference |
Reference is usually FZ.
#: Optional to be used in hemifield
studies. LT & RT 10 cm lateral to midline on both temporal regions.
Technical details
Dark room.
Patient seated 1 metre from screen.
Corrective lenses used if necessary
(acuity check prior to commencement of VEP).
200 sweeps.
Stimuli at 2 Hz.
Interpretation
|
Monocular VEP abnormality: |
This abnormality suggests a
conduction defect in the left/right visual pathway anterior to the optic
chiasm. Although demyelinating disease is the most common aetiology for such
a finding, various other possibilities cannot be excluded eg retinal disease
and compressive lesions of the optic nerve. |
|
Binocular VEP abnormality:
|
These abnormalities suggest
conduction defects in the visual pathways bilaterally. However, because of
the binocular nature of the findings, the lesion location (retina, optic
nerve, tracts or radiations) cannot be determined. |
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