Visual evoked potentials in neurological diseases
Light triggers a chemical reaction in the retinal photoreceptors. Electrical signals are transmitted through all neurons of the visual pathway into the visual cortex. Resulting potential fluctuations can be derived as visually evoked potentials (VEP) and analyzed regarding latency and amplitude in order to get an indication of pathological changes within the visual pathway.
This article shall explain the processes leading to the emergence of potentials in the visual cortex, which methods and techniques of VEP are available and in which neurological diseases a clinical added value for finding a diagnosis is given.
In VEP, a response of all neurons is represented, which is mainly generated by central visual field components. In order to be able to represent pathologies, that affect only partial areas of the visual field, the measurement technique of multifocal evoked potentials (mfVEP) was invented, with which potentials can be assigned to certain retinal areas. In neurology, VEP are mostly used for testing for optic neuritis, mainly in the context of multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD). In MS, latency delay and amplitude reduction are typical in the acute stage, after subsiding only latency delays are typical. In NMOSD, a very strong reduction of the amplitude is a typical sign. MfVEP confirm pathological changes of VEP, but also show a central amplitude reduction in MS, while in NMOSD the central potentials are almost extinguished. In other neurological diseases, changes in VEP may occur, but are not specific, therefore they do not bring any additional clinical benefit to the diagnosis.
In neurological diseases, VEP can show specific changes, especially in optic neurites, and can therefore bring clinical added value in finding a diagnosis.
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