Update on the range of visual electrophysiology tests and heir application with clinical examples

Abstract

The International Society for clinical electrophysiology of vision (ISCEV) publishes open‐access standards and guidelines for routine electrophysiological tests of the visual system in order to optimize diagnostic value, to promote consistency and to allow meaningful inter‐laboratory comparisons. The ISCEV also publishes extended protocols with the aim of promoting convergence of methods that are not yet standardized, for tests that are widely used but often performed as an addition to the minimum ISCEV standard procedures (see www.ISCEV.org for all publications).This talk will outline the main ISCEV standard methods including the full‐field electroretinogram (ERG), pattern ERG (PERG) and multifocal ERG (mfERG). Several extended full‐field ERG protocols will also be highlighted, including the dark‐adapted (DA) red flash ERG, photopic On–Off ERG and S‐cone ERG. The use of these methods in the clinic will be illustrated in cases of inherited and acquired retinal disorders, to show how the extended protocols complement standard techniques, to aid diagnosis and patient management and to probe and detail retinal function phenotypes.The Standard full‐field ERG is recorded under dark‐adapted (DA) and light‐adapted (LA) conditions and provides a measure of generalized rod and cone system function at the level of the outer and inner retina, with minimal contribution from the macula. The mfERG assesses cone system function across the posterior pole and the PERG assesses macular and macular retinal ganglion cell function.The DA red flash ERG is an extended protocol that provides a measure of generalized dark‐adapted retinal function, with the advantage of having both a cone system x‐wave and a rod system b‐wave within the same waveform. This enables the relative involvement of rod and cone systems to be assessed simultaneously and can help determine the origins of severely attenuated standard DA strong flash ERGs. The DA red flash ERG is also useful for assessing cone system function in photophobic patients, and in patients with variable ability to comply with longer ERG protocols. The photopic On–Off ERG is a response to an extended light stimulus (duration 150 or 200 ms) and is used to assess generalized cone system function of both the On and Off retinal pathways, useful when there is a locus of dysfunction that is post‐phototransduction or post‐receptoral, when On and Off retinal systems may be similarly, selectively or specifically affected e.g., in different forms of congenital stationary night blindness (CSNB) or in forms of toxic retinopathy. The S‐cone ERG (short‐wavelength or “blue” flash ERG) is used to probe the function of the S‐cone retinal pathway, and can aid diagnosis and characterization in a variety of retinal dystrophies and disorders e.g., distinguishing between achromatopsia and S‐cone monochromacy.