Visual Evoked Potentials

The derivation of visual evoked potentials (VEP) is used for the diagnosis of pathological changes in both ophthalmology (eye medicine) and neurology (medicine of the nervous system). It involves electrical voltage changes derived by electroencephalogram (EEG) over the primary visual cortex (area in the cerebral cortex responsible for processing visual sensations) while the patient is exposed to visual stimuli. The examination allows assessment of the optic nerve, the visual pathway, and the visual cortex. In addition to visual evoked potentials, the following related examinations exist:

  • SEP – Somatosensory evoked potentials: small electrical signals stimulate peripheral sensory nerves (at the extremities) so that the response of the sensory neural pathways over the postcentral gyrus of the contralateral hemisphere (area in the brain responsible for processing sensitivity) can be inferred.
  • AEP – Auditory Evoked Potentials: repetitive clicking sounds irritate the patient’s auditory pathway so that the response of the sensitive neural pathways over the vertex (apex of the skull) and mastoid (temporal bone) can be derived.

The indications (applications) for performing a visual evoked potentials derivation are many: any visual pathway disorder starting with the retina (retinal) and ending with the primary visual cortex (primary visual cortex) are detectable.

Indications (areas of application)

  • Anton’s syndrome (cortical blindness) – visual anosognosia (misrecognition) of one’s own (cortical) blindness after damage to the visual pathways of both hemispheres of the brain.
  • Autosomal dominant optic atrophy – hereditary atrophy (atrophy) of the optic nerve.
  • Glaucoma – glaucoma
  • Endocrine orbitopathy (EO) – disease of the eye socket (orbit); it is one of the organ-specific autoimmune diseases, which usually occurs in the presence of thyroid dysfunction and is characterized by a so-called exophthalmos (protruding eyes).
  • Ischemic optic neuropathy – damage to the optic nerve pathway due to decreased blood supply.
  • Compression or injury of the optic pathway by tumors.
  • Leber’s optic atrophy – hereditary atrophy (atrophy) of the optic nerve, named after the first describer, Dr. Theodor Leber.
  • Maculopathies – diseases of the macula (yellow spot – place of sharpest vision) such as age-related macular degeneration (AMD).
  • Multiple sclerosis (MS) – chronic inflammatory demyelinating disease of the central nervous system (CNS).
  • Neurolues (synonym: neurosyphilis) – set of characteristic psychiatric or neurological symptoms that can occur with a latency period of years to decades in untreated or uncured syphilis disease.
  • Optic neuritis (optic neuritis).
  • Optic trauma (optic nerve injury)
  • Retinal ischemia – deficiency of blood supply to the retina.
  • Traumatic brain injury (TBI)
  • Disorders of the central visual pathway due to tumors or vascular problems.
  • Uveitis – inflammation of the middle skin of the eye, which consists of the choroid (choroid), the corpus ciliare, and the iris
  • Changes in the optic discs (exit site of the optic nerve from the eyeball).
  • Toxic damage to the nerve pathways caused by tobacco, alcohol or ethambutol (tuberculostat).

The procedure

The examination procedure is as follows: The patient is exposed to a visual stimulus consisting of either a checkerboard pattern with rapidly changing contrast reversal or alternating flashes of light. Meanwhile, VEPs are recorded at the occipital pole via an electrode as in electroencephalography (EEG). Since at any time spontaneous neuronal activity appears as noise in the EEG, the visual evoked potentials have to be averaged several hundred times to be recognizable as potential changes. For this reason, both the stimulus patterns and the defined stimulus strength or stimulus magnitude are constant. This procedure is also called averaging. Normally, the EEG curve shows a characteristic potential change that allows a diagnostic assessment. Positive and negative deflections occur after a defined latency period, so that changes represent indications of a pathological event.For example, the latency of the first pronounced positive potential change visible in the EEG is usually about 90-120 ms and is called the P100 component. This is the time from excitation of the photoreceptors on the retina to the arrival of excitation in the visual cortex. In certain diseases, such as multiple sclerosis (MS – chronic inflammatory demyelinating disease of the central nervous system (CNS)), the P100 latency is prolonged. The evaluation of visual evoked potentials allows an informative diagnosis of various disorders and diseases of the complete visual pathway and thus represents a valuable component of neurological and ophthalmological diagnostics. Especially in cases of suspected multiple sclerosis, the examination is important on the way to diagnosis.