ISCEV extended protocol for the dark-adapted red flash ERG

Abstract

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG standard, namely the dark-adapted (DA) red flash ERG. The DA red flash ERG can be incorporated conveniently within the ISCEV standard ERG protocol after a minimum of 20-min DA and recorded after the DA 0.01 ERG to a flash strength of 0.3 phot cd s m^-2, eliciting a waveform with two positive peaks in healthy individuals. The first positive component is the cone-mediated x-wave with a peak at 30-50 ms; the second is a rod-mediated b-wave with a peak time of approximately 100 ms. Shorter DA times may be desirable to shorten the recording time or to alter the prominence of the early cone-mediated x-wave relative to the rod-mediated b-wave. The DA red flash ERG is used to aid the diagnosis of achromatopsia (rod monochromacy), cone dystrophy and other forms of cone system dysfunction, including "Bradyopsia" (RGS9/R9AP-retinopathy), when the DA red flash ERG x-wave is preserved in the absence of ISCEV standard LA ERGs. The DA red flash ERG can also help determine the origin of residual DA ERGs in cases of severe rod dysfunction, for example in disorders such as vitamin A deficiency, fundus albipunctatus (RDH5-retinopathy), Oguchi disease (SAG- or GRK1-retinopathy) and some rod-cone dystrophies. To shorter DA periods, the x-wave may be elicited without the following rod b-wave, shown to be helpful in abbreviated protocols for children.

Keywords: Clinical standards; Dark-adapted (DA); Electroretinogram (ERG); Full-field ERG; International Society of Clinical Electrophysiology of Vision (ISCEV); Red flash ERG; Retinal dystrophy.

Fig. 1

An ISCEV standard DA 0.01 ERG is shown at the top of the figure to compare the waveform of the rod driven b-wave with that of DA red flash ERGs produced by three different flash strengths of wavelength 635 nm after 20-min dark adaptation. Note the separation in peak time of the x-wave and b-wave to DA 0.03 cd s m⁻² (dim) flashes, the enlargement of the x-wave to DA 0.3 cd s m⁻² and the merging of x- and b-waves at DA 3 in a control subject. Insert i shows the spectral characteristics of the red (solid line) and blue (dotted line) LEDs in the Ganzfeld. Insert ii shows the DA red flash ERG to 0.3 cd s m⁻² in a second subject compared with a DA blue flash ERG of “scotopically matched” b-wave amplitude, in this case DA blue 0.0003 cd s m⁻² (the red flash response may also be “matched” to a DA dim white flash ERG). DA red ERG is shown as a solid black lines and DA blue flash ERG as a dotted line

Fig. 2

The gradual change in waveform of DA red flash ERG to a range of flash strengths weaker or stronger than 0.3 cd s m⁻², recorded after 20 min DA with a 650 nm red flash