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Visual evoked potentials
Last reviewed: 18.10.2021
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Visible evoked potentials (VEP) are recorded to diagnose lesions of the visual pathways, assessing their condition from the peripheral (retina) to the central divisions (primary and secondary visual centers). The method of registration of visual evoked potentials for a flash of light and a reversal pattern is widely used in the clinic for the diagnosis of diseases of the visual pathways and pathology of the optic nerve, with swelling, inflammation, atrophy, compression injuries of traumatic and tumor origin, localization of the pathological process in the chiasmis, visual tract and cortex of the head brain, amblyopia and retinal diseases.
The visual evoked potentials reflect mainly the electrical activity of the macular area, which is due to its abundant representation as compared to the periphery in the spur groove. As stimuli, diffuse flashes of light and spatially structured stimuli in the form of chess patterns and lattices with a rectangular luminous profile are usually used. The types of visual evoked potentials depend on the nature of the stimulus: the visual evoked potential for a flash of light is called a flare, the pattern-stimulus is a pattern-PEP. When registering this form of visual evoked potentials, the stimuli are presented either in the on-off mode, when the average illumination of the pattern and the homogeneous field that replaces it is constant, or in the reversal mode, when in the constantly visible screen of the chess field the white squares are replaced by black ones, white. The visual evoked potentials on the flare allow obtaining approximate information about the state of the optic nerve and the visual pathway above the chiasma.
Spotted evoked potentials complement the results of electroretinography and are the only source of information about the visual system in cases where ERGs can not be registered for one reason or another.
Criteria for clinically significant abnormalities in the evaluation of visual evoked potentials are the absence of response or a significant decrease in amplitude, lengthening of latency of all peaks, significant differences in amplitude and latency in stimulation of the right and left. In newborn or non-contact patients, normal visual evoked potentials do not yet prove the presence of consciousness and perception of visual images, but can only indicate the preservation of photosensitivity.
Fluorescent angiography, ultrasound, scanning laser ophthalmoscopy, and optical coherence tomography also play an important role in the differential diagnosis of retinal and choroidal diseases.
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