Metrovision's Multifocal ERG and VEP

Principle

This exam creates a map of electrical responses from the retina (mfERG) or from the visual cortex (mfVEP).

The visual stimulator generates a matrix of 16 to 217 zones that are stimulated with independent sequences of flashes. The global ERG response (or VEP) is recorded from a unique electrode.
Local responses are obtained by computing the inverse correlation between this global ERG response and the stimulation sequence.

Highly innovative stimulation technology

Controlling stimulus luminance and timing is very important for multifocal exams

This is achieved thanks to the proprietary LED technology of the MonPackONE.
It produces very high luminance stimulations (up to 600 cd/m2) resulting in responses of high signal to noise ratio and reduced examination time
The LED backlight produces short flashes of light interespaced with dark intervals, resulting in a timing accuracy better than 1 ms.

• MonPackONE PDF brochure Information Request

Multifocal stimulations

A compromise needs to be made between resolution, examination time and signal/noise ratio.

The number of stimulation zones is comprised between 19 and 217.The number of stimulated zones must be a compromise since, as this number increases, the accuracy of fixation and the recording time increase. For 61 stimulation zones, the typical recording time varies from 60 to 300 seconds, depending on the cooperation of the patient.

Map of local responses

During the exam, the program displays in real time the local responses with an automated identification of the N1, P1 and N2 peaks of each response.
The quality of the recorded signal is evaluated by computing the noise level and displaying the signal evolution since the beginning of the recording (base line).
In the example hereby, the base line appears very unstable at the beginning of the exam, which is frequently due to eye movements, eye blinks or electrode instability.
After about 1 minute, the baseline becomes stable and the noise level indicates that the quality of result is sufficient for a valid interpretation.

2D and 3D maps

The program allows to display 2D and 3D interpolated maps of the amplitude and implicit time of the N1, P1 and N2 peaks of the local responses.

Statistical analysis

The ring ratio analysis greatly improves the detection of early alterations.

The program performs a comparison of analysis results within given zones with a normal subjects data base from several clinical centers. Quantitative measurements of amplitude and implicit times outside the normal range are immediately outlined with a color code.
In addition, the program performs a ring ratio analysis (comparison between central and peripheric responses) that improves significantly the detection of central alterations.

Comparison with the eye fundus

This analysis allows the superposition of the map of local mfERG responses over the image of the eye fundus of the patient. The image of the eye fundus is imported as an image file either through the computer network or by USB key, CDROM etc. The operator identifies the position of the fovea and papilla to obtain a precise superposition.

Optical correction and fixation monitoring

The accurate correction of refractive errors is important for the quality of MfERG results

Metrovision proposes set of "large field" eye glasses that avoid masking artifacts of the peripheral visual field.
In addition, the high resolution video camera allows an accurate control of fixation by the operator. As an option, Metrovision proposes an automated fixation control that analyses the image of the eye in realtime to reject responses in case of blink and eye movement.

• PDF brochure on optical set Information Request