ISCEV standard for clinical multifocal electroretinography (mfERG) (2021 update)

Abstract

The multifocal electroretinogram (mfERG) is an electrophysiological test that allows the function of multiple discrete areas of the retina to be tested simultaneously. This document, from the International Society for Clinical Electrophysiology of Vision (ISCEV), presents an updated and revised ISCEV standard for clinical mfERG and defines minimum protocols for basic clinical mfERG recording and reporting so that responses can be recognized and compared from different laboratories worldwide. The major changes compared with the previous mfERG standard relate to the minimum length of m-sequences used for recording, reporting of results and a change in document format, to be more consistent with other ISCEV standards.

Keywords: Clinical standards; Electroretinogram; International Society for Clinical Electrophysiology of Vision (ISCEV); Multifocal electroretinogram.

Fig. 1

Typical mfERG-stimuli showing hexagonal frames scaled to be larger with increasing eccentricity and containing A 61 elements or B 103 elements. Individual hexagon outlines are added for clarity. The horizontal extent (arrows) of the stimulus array for standard mfERG recordings ranges between 40° and 50°

Fig. 2

Sample mfERG recording obtained to a stimulus array containing 103 elements. A Traces (left eye; field view) from different eccentricities are arranged in an equidistant manner for clear visualization and comparison, while the actual stimulus array is scaled (see Fig. 1b). B 3D-response density plot (field view). Overall signal strength is given per unit area of retina. C Ring-averages. MfERG traces from the concentric hexagons were averaged within six different eccentricity ranges (see color coding in stimulus schematic) and arranged vertically from center to periphery. MfERG peak definitions (N1, P1, and N2) and P1-amplitude (trough to peak, vertical arrow) and P1-peak time (horizontal arrow) measures are indicated for the foveal response. The horizontal broken line corresponds to the trough of the N1 component

Fig. 3

Sample mfERG recording to a 61-element array from a healthy control and illustrations of induced artifacts. Trace arrays (left column) and 3D-response density plots (right column) are depicted in field view (left eye). A Control (“normal”) recording for reference. B Eccentric fixation. To mimic eccentric fixation, the target was positioned in the lower right visual field (blue cross), where, as a consequence the responses were largest, while they were smallest in the stimulus center. C Unstable fixation. To mimic unstable fixation, the participant shifted the gaze between the three central horizontal hexagons (blue dashed line). This created a response reduction in the stimulus center and an enlargement for the lateral hexagons. D Positioning error/rim artifact. The view was obscured by the rim of the trial frame, resulting in attenuation of eccentric superior and superior-temporal responses

Fig. 4

Artifactual central peak. An example of a 61-element “mfERG recording” from a healthy control while the monitor was switched off (trace array and 3D-response density plots). No central response is evident in the trace array, but there is a central peak in the corresponding 3D plot, due to an automated scaling of signals relative to the area of a stimulus element. Noise associated with each hexagon is approximately similar, resulting in increased noise density for smaller hexagons. Note the difference in response density scaling compared with Fig. 3