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Multifocal Electroretinography
Last reviewed: 23.04.2024
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[When using multifocal electroretinography
Although most of the answers for: electroretinography come from the outer layers of the retina (photoreceptors, bipolar cells), multifocal electroretinography is also used for an objective evaluation of ganglion cell function. Some of the response signals come from the fibers of the ganglion cells located next to the optic nerve disc. This component in patients with glaucoma is understated. This method does not require the dilatation of the pupil. Special systems have been developed that study the amplification, isolation, and mapping of this component of the response.
How does multifocal electroretinography work?
When receiving an electroretinographic signal from the cornea through the contact lens of the electrode, all focal zones are independently and simultaneously excited. A special mathematical scheme of multifocal stimulation allows you to accurately extract the delivered focal responses from a single electroretinographic signal. Do not answer patients' questions. When using the Visual Evoked Response Imaging System (VERIS; Electro-Diagnostic Imaging, San Mateo, CA ), the stimulus can consist of several hundred focal stimuli. As a rule, 103 hexagonal sections depicted on a video monitor stimulate the central 50 ° field of view of the patient. In most cases, focal stimulation consists in the pseudorandom presentation of flares. Local electrophysiological response signals are topographically collected and recorded, forming functional retinal maps, similar to the field of vision field maps.
Restrictions
Currently, multifocal electroretinography is used experimentally, it is not included in the routine clinical examination.
Caused visual cortical potentials
Caused visual cortical potentials (SEM, or visual evoked responses) are electrical signals generated by the visual cortex of the occipital lobe of the brain in response to stimulation of the retina by light flashes or pattern-stimuli. To assess the condition of the visual pathways, because of the increased sensitivity in determining the violations of axonal conduction, it is preferable to use non-flare ZVKP, and the ZVKP pattern.
How the evoked visual cortical potentials work
The method of BEP measures the electrical response of the visual cortex of the brain to a pattern or flare stimulus. The potential of visual evoked responses is measured between the electrodes on the scalp. One electrode, measuring the response itself, is located above or lateral to the outer occipital tuberosity (or ation), close to the main visual cortex. The other electrode is located at the control point. The last electrode is used for grounding.
When the evoked visual cortical potential is applied
Initially, PBCC was used to determine the secondary loss of vision in optic nerve diseases and the damage to the anterior visual pathways.
The multifocal method described in the previous section is also used to record cortical responses (multifocal WBCs). In this case, the order of stimuli is usually formed as a "dart" pattern, where each sector contains contrasting reversible stimuli in a checkerboard pattern. The difficulty of this method lies in the reduction or absence of local responses in part because of the anatomical tortuosity of the cerebral cortex. This method does not always reflect a function violation. One-sided local disturbance of the function is revealed when comparing the two-eye response cards. In recent studies, correlations have been revealed between SLEV and visual field defects.
Restrictions
Similar to the limitations of multifocal electroretinography, it is necessary to do a great deal of work with multifocal electroretinography before general clinical adaptation of this method.