Which factors influence results of visual evoked potentials (VEPs)?

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

Answer

The usual VEPs are evoked by checkerboard stimulation. Because the cells of the visual cortex are maximally sensitive to movement at the edges, a pattern-shift method is used, with a frequency of 1-2 Hz. The size of the checks affects the amplitude of the waveform and the latency of the P100.

In addition, pupillary size, gender, and age all affect the VEP. Deterioration of visual acuity, up to 20/200, does not alter the response significantly; large checks may be required. In some studies, women have slightly shorter P100 latencies. Sedation and anesthesia abolish the VEP. Some subjects, by fixating beyond the plane of stimulation, may alter or suppress P100 altogether.

Certain drugs (eg, carbamazepine) prolong VEPs. In a study of the effects of carbamazepine and sodium valproate monotherapy on VEPs in 18 epileptic children, Yuksel et al found that carbamazepine slows down central impulse conduction. [5] . Pattern-reversal VEPs were determined before administration of the antiepileptic drugs and after 1 year of therapy; the VEP amplitude showed no consistent changes after 1 year of therapy, but VEP P100 latencies were significantly prolonged after 1 year of carbamazepine therapy.

According to Trip et al, atrophy of the optic nerve was correlated with decreased VEP amplitude. [6]

Sannita et al evaluated the correlation between amplitude and latencies of the pattern-reversal VEP and serum glucose level in healthy volunteers. Pattern VEP and serum glucose levels were obtained at 2-hour intervals during an 8-hour experimental session. At serum glucose concentrations within the physiological range of variability (55-103 mg/dL), the P100 latency increased with increasing serum glucose level, with a 6.9% estimated latency difference between lower and higher glucose concentrations. [7]


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