The dark-adapted human electroretinogram (ERG) response to a standard bright flash includes a negative-going a-wave followed by a positive-going b-wave that crosses the baseline. An electronegative waveform (or negative ERG) results when the b-wave is selectively reduced such that the ERG fails to cross the baseline following the a-wave. In the context of a normally sized a-wave, it indicates a site of retinal dysfunction occurring after phototransduction (commonly at the photoreceptor to bipolar cell synapse). This is an important finding. In genetic disease, the pattern of ERG abnormality can point to variants in a small group of genes (frequently those associated with congenital stationary night blindness and X-linked retinoschisis, but negative ERGs can also be seen in other conditions including syndromic disease). In acquired disease, there are numerous causes, but specific features may point to melanoma-associated retinopathy (MAR). In some cases, the visual symptoms precede the diagnosis of the melanoma and so the ERG findings can initiate investigations facilitating early detection and treatment. Negative ERGs can occur in other paraneoplastic conditions, and in a range of other diseases. This review will outline the physiological basis for the negative ERG, report prevalences in the literature from different cohorts, discuss the range of causes, displaying examples of a number of ERG phenotypes, highlight features of a clinical approach to patients, and briefly discuss further insights relating to current flows shaping the a-wave trough and from single-cell transcriptome analysis.
Significance Myopia prevalence has increased dramatically over recent decades. Genome-wide association studies have identified numerous loci, but mechanisms by which genotypic identity confers myopia susceptibility are unknown. The common variant most strongly associated with myopia is near a gene encoding retinal gap junctions. We analyzed retinal electrophysiological responses from 186 twins genotyped at this locus, finding association between cone-driven, but not rod-driven, electroretinogram signals and allelic genotype. Examination of responses to further, nonstandard testing protocols, together with recordings from patients with selective loss of bipolar cell signals, points to an effect on cone-driven hyperpolarizing (“OFF”) signals. The pattern of retinal expression of this gene appears consistent with these findings, which support a potential role for altered cone-driven signaling in myopia development.
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