What are pitfalls in the use of visual evoked potentials (VEPs) for clinical use?

Updated: Oct 25, 2019
  • Author: Andrew B Evans, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Answer

A check size of 27 seconds of visual angle may result in normal P100 latency in a patient with cortical blindness; smaller checks (ie, ≤ 20 seconds of visual angle) should be used to demonstrate the abnormality. If cortical blindness is suspected, large checks should not be used.

In conditions such as retinal disease or refractory errors, the amplitude may be smaller and, at very small check sizes, the latency may increase. For this reason, proper refraction is of great importance.

Because the VEP measures the pathway from the retina to area 17, a normal P100 does not exclude lesions of the visual pathway beyond area 17. Consequently, the VEP may be normal in patients with the diagnosis of cortical blindness. Note that in such cases, the VEP is still useful, in that it rules out disease up to area 17 in patients with a normal response.

The usefulness of VEP is limited in malingering and hysterical visual loss. It is useful when a normal VEP is recorded, but abnormal responses are of limited diagnostic value in such cases. Baumgartner et al reported that as many as 5 of 15 healthy subjects were able to suppress their pattern VEPs. [8]


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