Visual evoked potential

Visual evoked potentials (VEP, including: VECP = visually evoked cortical potentials ) are caused by visual stimulation of the retina potential differences of low electrical charges that can be derived over the area of the visual cortex at the back of the skin. They are used in neurology and ophthalmology as a diagnostic procedure and allow an objective detection of sensory stimulation leads to the cerebral cortex. The measurement of latency time (duration ) and amplitude ( extent of excitability ) of the potentials are clues to the function of the visual pathways and their components ( the optic nerve, visual cortex ). The visual stimulation takes place either with light pulses or with a checkerboard pattern, in which the contrast in short intervals to be reversed. In healthy people, the latency of the primary cortical potential is 100 milliseconds. On the monitor, a negative deflection is to recognize.

In circulatory disorders, degenerative processes and inflammation in the area of the visual pathway, the latency can be delayed and / or reduced the amplitude. VEPs play especially in the diagnosis of multiple sclerosis an important role.

Interpretation of the values

A typical VEP has a valley of its potentials at about 80 ms ( N80 ), a peak at 100 ms (called P100 ) and another minimum at about 135 ms ( N135 ). Measured the latency of the P100 and the amplitude is measured as the difference N80 either P100 or a mean difference ( ( P100- N80 ) ( P100- N135 )) / 2 The latency is in the broadest sense, a value for the time required for a stimulus light from the retina of the eye as a pulse voltage to the visual cortex in mind. It is located in the normal population in the range of 95-115 ms. The amplitude is in the range of 5 to 30 microvolts microvolts.

The classic application of VEPs is the diagnosis of visual pathway and their components ( the optic nerve, visual cortex ), eg in the context of multiple sclerosis. In inflammation in the field of the visual pathway, the latency is increased significantly ( to 20 ms or more), the amplitude is reduced little. Also VEPs allow the assessment of the severity of amblyopia and therefore find in the strabologischen diagnostic application.

  • A slight latency ( delay ) at normal amplitude indicates a demyelination. The amplitude can be reduced in this case also.
  • A strong delay of the signal at a normal amplitude is indicative of demyelination and remyelination.
  • A fragmented and delayed stimulus response indicates a chronic de-and remyelination.
  • No irritant response points to the complete damage to the axons or the fact that there is a line block, which may be caused by a tumor.
  • A low stimulus response ( voltage potential ) and a normal latency ( delay ) indicates a partial damage to the axons, or upon a partially existing conduction block.

The REE are highly dependent on technical parameters of stimulation (monitor, mirror, flash glasses, distance to the eye). Therefore, it is mandatory that any particular configuration specific standard values ​​are determined. There is also a function of age with a slow increase in the latency from the age of 55.

Chessboard Werner Hacke
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