Dark-adapted red flash ERGs in healthy adults

A review of electroretinography waveforms and models and their application in the dog

Electroretinography (ERG) is a commonly used technique to study retinal function in both clinical and research ophthalmology. ERG responses can be divided into component waveforms, analysis of which can provide insight into the health and function of different types and populations of retinal cells. In dogs, ERG has been used in the characterization of normal retinal function, as well as the diagnosis of retinal diseases and measuring effects of treatment. While many components of the recorded waveform are similar across species, dogs have several notable features that should be differentiated from the responses in humans and other animals. Additionally, modifications of standard protocols, such as changing flash frequency and stimulus color, and mathematical models of ERG waveforms have been used in studies of human retinal function but have been infrequently applied to visual electrophysiology in dogs. This review provides an overview of the origins and applications of ERG in addition to potential avenues for further characterization of responses in the dog.

ISCEV extended protocol for the dark-adapted red flash ERG

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.