Veris Multifocal ERG

Multifocal ERG for the Presence and the Future

Since end of 1998 Cephalon A/S has worked with VERIS Multifocal ERG. Today Cephalon is the European Agent and distributor of the VERIS Multifocal system! For further information please do not hesitate to contact us.

Therefore we are proud to offer you the most advanced system on the market, invented by Erich Sutter, PhD, in the Smith-Kettlewell Eye Research Institute in San Francisco.

If you are interested in the basics of Multifocal ERG, feel free to take a look at a typical multifocal recording setup, drawn by Marc A. Bearse, PhD at the Smith-Kettlewell Eye Research Institute in San Francisco.

For additional informations follow our Introduction in VERIS Multifocal ERG and find a list of publications on multifocal ERG on the homepage of ElectroDiagnostic Imaging Inc.

Clinical & Research applications

The principle Multifocal ERG is an advanced technology based on the standard Electroretinogram. When the retina is exposed with changing light levels its current generated by the neural activity in the retina changes too. This current can be measured using an electrode attached to the eye. A bipolar contact lens electrode - as the Burian-Allen type - or a unipolar electrode - as for instance wire electrodes, may be used. Especially powerful and therefore interesting to evaluate is the impulse reaction that comes from a flash or other fast changes in contrast

Components of an ERG signal The components that make up an ERG response are: large cone and rod response, small contribution from ganglion cell and optic nerve head component. The graph shows averaged ERG signals over concentric rings of the retina. (Signal 1 is in the fovea, signal 6 is about 20° off center.)

Benefits

Standard versus Multifocal ERG: Standard ERG as full field ERGs are widely used. Standardized recordings, measurement protocols and procedures allow the comparison of results. Since it uses fairly large stimuli to test large retinal areas at a time, focal damages cannot be detected this way. In addition, early retinal disease probably affect small areas on the retina. In multifocal ERG you test locally with focal stimulation. A high resolution functional map of the retina is obtained in the same amount of time it would take to record from only one small focal area with conventional ERG.

How to stimulate multiple spots simultaneously Multifocal ERG projects a changing pattern, unlike the single spot used in conventional ERGs. The pattern changes "pseudo random" according to so called m-sequences. This algorithm guarantees that no stimulus sequence is repeated during an examination and all stimulus patterns appear only once. This is the condition that must be met to allow to "divide the multiplexed signal" from the contact lens electrode into separate signals for every test location.

Summary Instead of a single stimulus and a single response you have a stimulus pattern of usually 61 to 241 hexagons covering up to +/- 25 degrees of the visual field and an underlying mathematical system that derives the true signal from each location.

Capabilities What makes the multifocal ERG so powerful for diagnostic purposes? The ERG consists of different components that are caused by different "signal sources" such as cone and rod response, small superimposition of ganglion cell and optical nerve head responses, and delayed signals of optical nerves behind the spot. By using suitable frame patterns you can extract one or another components better. Altough you can get rod and cone response with conventional ERG you cannot map them. Multifocal stimulation is necessary to extract the ONHC generated by retinal ganglion cells

Available configurations

VERIS^TM Clinic and Science
VERIS always consists of a control unit, based on an Apple Power Mac G5 or G4 iBook computer and a stimulation unit. The following stimulation units are available:

 

	VERIS Standard 21" This is the original system with a customized high luminance 21" monitor. It allows binocular examination and is well suited for all kinds of clinic applications and age groups. The refractive camera is optionally available for this system
	VERIS Compact   A system with integrated pupil camera and 7" examination monitor. An easy to use configuration.
	VERIS Fundus   A sophisticated tool that allows to see the fundus picture of the area which is being stimulated. Besides it also includes the refractive pupil camera enabling the examiner to switch between the pupil picture and the fundus image on the computer screen. This system is especially suited for animal research and retina replacement development as well as - of course - objective stimulation area control.

Unique features

• High maximum luminance of 600cd/m² allows examination with undilated pupil
• Examination field approx. 50° (±25°)
• Recording and analysis protocols for fast preparation and data evaluation
• Freedom in definition of new examination procedures and patterns (VERIS Science)
• High quality ERG amplifiers and calibration instrumentation
• Binocular examination supported with VERIS Standard 21"
• Optional Pupil camera with refractive correction for eye monitoring