ISCEV Standard for full-field clinical electroretinography (2008 update)

Chromatic stimuli offer certain advantages in the separation of cone and rod ERGs, but the calibration of colored stimuli and the relation of the ERGs produced by them to the standard ERG require special procedures. White flashes should be used for the standard ERGs, whether or not other stimuli are used in addition.

White stimuli produced by a combination of narrow band sources, such as red, green, and blue light-emitting diodes (LEDs), may not be equivalent to broad-band white light as a stimulus for both rods and cones. Manufacturers must ensure that appropriate photopic and scotopic filters are incorporated into their stimulation and calibration systems so that stimulus output is equivalent to the standard for all conditions. Separate scotopic calibration may be necessary for LED systems, and if so the proper stimulus for eliciting rod ERGs will be 2.5 log units below a scotopically-calibrated standard flash. The word ‘intensity’ is widely used to describe the luminance of surfaces. However, in photometry, ‘intensity’ quantifies the light from a point source. Luminance is the appropriate term for extended sources such as those used for ERG stimuli and backgrounds.

We recommend that the flash source of commercial instruments be capable of generating strengths at least 2 log units above the basic 3.0-cd·s·m⁻² flash and be attenuable through 6 log units below that same flash. Regardless of whether attenuation is achieved by filters or electronic means, we also strongly recommend that commercial units incorporate a means of inserting additional colored and neutral density filters. These capabilities will allow electrophysiologists to perform a variety of useful protocols beyond the Standard, and will meet possible future changes in the Standard. We also suggest that background luminance be adjustable to perform electro-oculography with the same equipment. Commercial units should also allow the insertion of colored and neutral density filters into the background illumination system to meet a variety of needs.

DC (direct-current) amplification can produce signals identical to those from AC amplification, but it is extremely difficult to use because of drift in baseline and offset potentials; we strongly advise AC recording except for laboratories with special requirements and expertise.

An overall index of oscillatory potential amplitude can be obtained by adding up measurements of the three major peaks, preferably from lines spanning the bases of the adjacent troughs, but alternatively from adjacent troughs directly (to allow use of measuring cursors with digitized systems). Some authors advise measurement of individual peaks.