Electroretinogram Protocol Research Articles

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

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.

Electroretinogram (ERG) to Evaluate the Retina in Cases of Retinitis Pigmentosa(RP).

Electroretinogram (ERG) captures the electrical responses of photoreceptors, the summation of action potentials from all neurons in the retina elicited by illumination. ERG testing is an incredibly useful tool in obtaining more specific information regarding a retinal dystrophy. Specifically, ERGs are typically used to test photoreceptors and inner retinal function in humans and animals, to diagnose retinal dystrophies, and to monitor disease progression. In this chapter, we will introduce the components of ERGs and the standard ERG protocols for clinical examination. We will also introduce the various specialized ERG tests, which can help to differentiate retinitis pigmentosa (RP) from other retinal disorders. Lastly, we will elaborate on how to use ERGs to predict visual prognosis in RP.

Flicker electroretinogram in newborn infants

PurposeTo develop and validate a flicker electroretinogram (ERG) protocol in term-born neonates as a potential tool for assessing preterm infants at risk of developing retinopathy of prematurity.MethodsA custom flicker ERG protocol was developed for use with the hand-held RETeval® electrophysiology device. Feasibility of measuring flicker ERG through closed eyelids and without mydriasis was established in a pilot study enabling optimisation of the test protocol. Following this, healthy term-born neonates (gestational age 37–42 weeks) were recruited at the Neonatology clinic of the University Hospital Zurich. Flicker ERG recordings were performed using proprietary disposable skin electrodes during the first four days of life when the infants were sleeping. Flicker stimuli were presented at 28.3 Hz for a stimulus series at 3, 6, 12, 30, and 50 cd·s/m2, with two measurements at each stimulus level. Results were analysed offline. Flicker ERG peak times and amplitudes were derived from the averaged measurements per stimulus level for each subject.Results28 term-born neonates were included in the analysis. All infants tolerated the testing procedure well. Flicker ERG recording was achieved in all subjects with reproducible flicker ERG waveforms for 30 and 50 cd·s/m2 stimuli. Reproducible ERGs were recorded in the majority of infants for the weaker stimuli (with detectable ERGs in 20/28, 25/28, and 27/28 at 3, 6, and 12 cd·s/m2, respectively). Flicker ERG amplitudes increased with increasing stimulus strength, with peak times concurrently decreasing slightly.ConclusionFlicker ERG recording is feasible and reliably recorded in sleeping neonates through closed eyelids using skin electrodes and without mydriasis. Flicker ERG amplitude decreases for lower luminance flicker but remains detectable for 3 cd·s/m2 flicker in the majority of healthy term-born neonates. These data provide a basis to study retinal function in premature infants using this protocol.

ISCEV Standard for full-field clinical electroretinography (2022 update)

The full-field electroretinogram (ERG) is a mass electrophysiological response to diffuse flashes of light and is used widely to assess generalized retinal function. This document, from the International Society for Clinical Electrophysiology of Vision (ISCEV), presents an updated and revised ISCEV Standard for clinical ERG testing. Minimum protocols for basic ERG stimuli, recording methods and reporting are specified, to promote consistency of methods for diagnosis, monitoring and inter-laboratory comparisons, while also responding to evolving clinical practices and technology. The main changes in this updated ISCEV Standard for clinical ERGs include specifying that ERGs may meet the Standard without mydriasis, providing stimuli adequately compensate for non-dilated pupils. There is more detail about analysis of dark-adapted oscillatory potentials (OPs) and the document format has been updated and supplementary content reduced. There is a more detailed review of the origins of the major ERG components. Several tests previously tabulated as additional ERG protocols are now cited as published ISCEV extended protocols. A non-standard abbreviated ERG protocol is described, for use when patient age, compliance or other circumstances preclude ISCEV Standard ERG testing.

An alternative electroretinography protocol for children: a study of diagnostic agreement and accuracy relative to ISCEV standard electroretinograms.

To assess the diagnostic accuracy and agreement between a paediatric electroretinography protocol used at Great Ormond Street Hospital (GOSH-ERG) and the 'gold standard' international protocol (ISCEV-ERG) in health and disease. Patient databases between 2010 and 2020 were screened to identify children with an ISCEV-ERG recorded within four years of a GOSH-ERG. Electroretinogram (ERG) component peak times and amplitudes were re-measured, and data were analysed in terms of absolute abnormality and proportional deviation from respective reference ranges. Abnormality was defined by the retinal system affected and by individual ERG a- and b-wave component analysis. A total of 59 patients were included: 38 patients had retinal disease defined by an abnormal ISCEV-ERG and 21 had normal ISCEV-ERGs. When absolute abnormality was defined by combined retinal systems, the GOSH-ERG showed an excellent overall sensitivity of 95% (accuracy 86%). Individual retinal systems showed good-excellent sensitivity (67%-100%) and specificity (68%-97%). Electroretinogram (ERG) component sensitivities ranged between 60% and 97% and specificities between 79% and 97% dependent upon the protocol step. The proportional relationship appeared mostly linear between protocols. Electroretinogram (ERG) morphology was comparable for both protocols in a range of retinal diseases including those with pathognomonic ERGs. We demonstrate the high diagnostic accuracy of a paediatric ERG protocol (GOSH-ERG) relative to ISCEV standard ERGs. The close proportional deviation and similar waveform morphology indicate ERGs from each protocol are similarly affected in disease. This encourages the use of the GOSH-ERG protocol in the screening, diagnosis and monitoring of retinal disease in children who are unable to comply with the rigorous ISCEV-ERG protocol.

Effects of DTL electrode position on the amplitude and implicit time of the electroretinogram

PurposeThis study sought to investigate whether there is an optimal position of the Dawson, Trick, and Litzkow (DTL) electrodes when measuring the full-field electroretinogram (ERG) for monitoring purposes.MethodsIn 200 uveitis patients, an extended light-adapted (LA) ERG protocol was measured twice, incorporating the International Society for Clinical Electrophysiology of Vision standards. First, a LA ERG was measured with the DTL in the lower lid position (LLP) and thereafter in the fornix position. Differences in amplitudes and implicit times of a-waves, b-waves, and the 30 Hz peak were investigated. Intraclass correlation coefficients (ICCs) as well as coefficients of variation (CoV) were calculated, to assess both reliability and relative variability between the two DTL positions.ResultsImplicit times showed no statistically significant differences between the two DTL positions. As expected, amplitudes at the different stimulus strengths were 1.12–1.19 higher in the LLP, but there were no significant differences in the CoV between the two DTL positions. The ICC was high for the b-wave and 30 Hz flicker response (0.842–0.979), but lower for the a-wave, especially for amplitudes (0.584–0.716).ConclusionsFor monitoring purposes in patients, we conclude that based on relative variability, no position is preferable above the other. However, because in most diseases amplitudes are decreased, the LLP may be chosen because it yields higher amplitudes. Whatever the choice, it is important to ensure that the DTL position remains stable during an ERG recording.

Optimizing a Portable ERG Device for Glaucoma Clinic: The Effect of Interstimulus Frequency on the Photopic Negative Response.

PurposeThe purpose of this study was to investigate the effect of interstimulus frequency on the photopic negative response (PhNR) in the clinical electroretinogram (ERG) in glaucoma and healthy eyes.MethodsParticipants with open angle glaucoma (n = 15) and age-matched controls (n = 20) were recruited. Photopic ERGs were recorded in one eye using five frequencies (1–5 Hz) delivered in random order. ERGs were analyzed for changes to amplitude and timing between groups and interstimulus frequency. Coefficient of variation (CoV) was used to examine variability within recordings for each frequency.ResultsWhile the a-wave and b-wave showed minimal alteration, the PhNR was highly sensitive to changes in interstimulus frequency. The PhNR signal was largest at 1 Hz and steadily diminished with higher frequencies in both control and glaucoma groups. Significant differences in PhNR amplitude were found between controls and glaucoma groups at 2 and 3 Hz. While 1 Hz delivered the largest PhNR, it also showed a significantly greater CoV compared to other frequencies.ConclusionsAn interstimulus frequency of 2 Hz was optimal for recording the PhNR, creating a good balance between testing time and signal quality. A higher frequency could be used to further shorten clinical testing times; however, this may compromise its clinical utility by dampening the PhNR.Translational RelevanceHere we show the importance of considering flash interstimulus frequency when designing ERG protocols for recording the PhNR as while higher frequencies can shorten test times, they also have considerable effects on the PhNR.

Electroretinograms in idiopathic infantile nystagmus, optic nerve hypoplasia and albinism.

To study electroretinograms in infantile nystagmus syndrome associated with idiopathic infantile nystagmus, optic nerve hypoplasia, and albinism. A total of 30 children with idiopathic infantile nystagmus, 18 with optic nerve hypoplasia, and 18 with albinism were studied. Three electroretinogram protocols were applied according to child's age: 58 (mean: 2.0 years) were recorded with skin electrode to Great Ormond Street Hospital protocol, 11 (mean: 5.3 years) with skin electrode to International Society for Clinical Electrophysiology of Vision protocol, and 7 children (mean: 12.2 years) with HK electrode to International Society for Clinical Electrophysiology of Vision protocol. The electroretinograms were compared to those of age-matched controls. Electroretinogram waveforms in idiopathic infantile nystagmus, optic nerve hypoplasia, and albinism were comparable to controls in all protocols. Electroretinogram amplitudes in idiopathic infantile nystagmus group showed increased white scotopic and photopic electroretinograms in 26 children (skin electrode to Great Ormond Street Hospital protocol), no difference to the controls in 3 children (skin electrode to International Society for Clinical Electrophysiology of Vision protocol), and increased rod electroretinogram in 3 children (HK electrode to International Society for Clinical Electrophysiology of Vision protocol). Optic nerve hypoplasia group showed increased white scotopic, photopic, and blue electroretinograms in 15 children (skin electrode to Great Ormond Street Hospital protocol); increased 30-Hz electroretinogram in 3 children (HK electrode to International Society for Clinical Electrophysiology of Vision protocol); and reduced combined rod-cone, cone, and 30-Hz electroretinograms in 3 children (skin electrode to International Society for Clinical Electrophysiology of Vision protocol). Albinism group showed increased white scotopic, photopic, and 30-Hz electroretinograms in 17 children (skin electrode to Great Ormond Street Hospital protocol), while it showed reduced cone and 30-Hz electroretinograms in 5 children (skin electrode to International Society for Clinical Electrophysiology of Vision protocol). Implicit times were shorter in albinism. Electroretinogram waveforms in idiopathic infantile nystagmus, optic nerve hypoplasia, and albinism were normal with mostly increased electroretinograms, while reduced electroretinograms did not show a specific pattern as in early-onset retinal dystrophies.

Reduction on OFF-responses of Electroretinogram in Monkeys with Long-term High Intraocular Pressure.

Background:There are ON- and OFF-pathways in the normal vertebrate retina. Short- and long-flash electroretinogram (ERG) are suitable methods to observe the function of ON- and OFF-pathways in vivo, respectively. It is clear that high intraocular pressure (IOP) might cause dysfunction of cone-dominated photopic negative response (PhNR) in monkeys with high IOP in ON-pathway. However, whether cone-dominated OFF-responses are also affected is less known. The aim of this study was to observe photopic OFF-responses of ERG in monkeys with high IOP.Methods:Nine monkeys were involved in the experiment from January 2006 to December 2016. High IOP was induced in the right eye by laser coagulation of the mid-trabecular meshwork in five monkeys. Six years after the laser coagulation, both short- and long-flash of the photopic ERG were recorded. Stimulus light was red flashes superimposed on a blue background. Four normal monkeys were examined under the same ERG protocols as controls. Paired t-test was used to compare the difference of each ERG parameter between the lasered eye and the fellow eye. Analysis of variance (ANOVA) with Tukey adjustment was adopted to calculate the differences among the lasered eye, the fellow eye, and the eyes of normal monkeys.Results:The mean amplitude of a-wave (11.73 ± 2.05) and PhNR (8.67 ± 2.44) in lasered eyes was significantly lower than that of a-wave (21.47 ± 3.15) and PhNR (22.05 ± 3.42) in fellow eyes (P = 0.03 and P = 0.01, respectively) in response to short flash. The mean amplitude of d-wave (1.60 ± 0.59) and i-wave (3.13 ± 0.64) was significantly reduced in the lasered eyes than that of d-wave (4.01 ± 0.56) and i-wave (8.79 ± 1.75) in the fellow eyes (P = 0.02 and P = 0.02, respectively) in response to long flash.Conclusions:Reduced OFF-responses are recorded in monkeys with high IOP when dysfunction of photoreceptor is involved. The reduced OFF-responses to long-flash stimulus show evidence of anomalous retinal circuitry in glaucomatous retinopathy.

Electrophysiological Studies on The Dynamics of Luminance Adaptation in the Mouse Retina.

To date, most studies involving in vivo electroretinography in mice are performed on steady state adapted animals. In this study, we focused on the dynamics of adaptation to high and low light levels in the mouse retina. Two flash electroretinogram (ERG) protocols and one flicker ERG protocol were employed. In the two flash ERG protocols, the animals were adapted to either 25 or 40 cd/m2 white light and ERGs were recorded for up to 15 min of adaptation. Afterwards, flash ERGs were recorded for up to 45 min of dark adaptation. Amplitudes of the flash ERG increased during light adaptation, while implicit times of the different wave components decreased. During subsequent dark adaptation, the amplitudes further increased. The increase in a-to-b-wave ratio indicated adaptational processes at the photoreceptor synapse. In the flicker ERG protocol, the responses to 12 Hz sinusoidal luminance modulation during the adaptation to 25 cd/m2 and a 1 cd/m2 mean luminances were recorded. The amplitudes of the first harmonic components in the flicker protocol decreased during light adaptation but increased during dark adaptation. This is at odds with the changes in the flash ERG, indicating that adaptation may be different in different retinal pathways.

Electroretinographic characteristics in children with infantile nystagmus syndrome and early-onset retinal dystrophies.

To differentiate early-onset retinal dystrophies on the basis of electroretinogram (ERG) characteristics in children with infantile nystagmus syndrome (INS). Thirty-seven children with INS and early-onset retinal dystrophies were included, with diagnosis according to clinical and ERG findings. Three ERG protocols were used according to the child's age and 17 children were followed with 2 protocols: 27 (mean 2.1 years) were recorded with skin electrodes to flash stimulation, 16 (mean 6.5 years) with skin electrodes to full-field stimulation, and 11 (mean 12.2 years) with HK electrodes to full-field stimulation. The ERGs were compared to those of age-matched controls, with differences significant if p<0.05. Clinical and electrophysiologic findings were in agreement across all of the children. In nine children with Leber congenital amaurosis, the scotopic and photopic ERGs were not recordable under all protocols. Six children with congenital stationary night blindness (CSNB) had electronegative scotopic ERG under all protocols, those with complete CSNB had absent rod ERG, and those with incomplete CSNB had reduced rod ERG. Eight children with achromatopsia had nonrecordable photopic and subnormal scotopic ERG under all protocols. The implicit times of the scotopic b-waves were prolonged. One child had blue-cone monochromatism and reduced photopic and normal S-cone ERG. Six children with cone-rod dystrophy without systemic disorder, and seven children with systemic disorder, had affected photopic and scotopic ERGs under all protocols. In children with INS, some early-onset retinal dystrophies can be differentiated through ERGs, also with skin electrodes.

Determinação dos valores normais do eletrorretinograma de campo total em cães da raça Poodle portadores de catarata de acordo com a faixa etária

Eletrorretinograma (ERG) é um meio diagnóstico objetivo, não invasivo e capaz de avaliar a função retiniana, detectando precocemente, em diversas espécies, lesões nas camadas mais externas. Tem como uma das principais indicações a avaliação pré-cirúrgica em pacientes portadores de catarata. A determinação dos valores normais do ERG é indispensável quando se objetiva, pela mensuração dos valores, o auxílio no diagnóstico das degenerações retinianas, mesmo quando apresentam opacidade de meios (catarata). Este estudo teve como objetivo padronizar os valores das respostas do eletrorretinograma em cães da raça Poodle portadores de catarata madura ou hipermadura, submetidos ao mesmo protocolo de sedação, adaptação ao escuro e eletrodo, utilizando aparelho portátil BPM 200. Em todos os animais, o exame oftalmológico precedeu o ERG. Os animais foram separados em quatro grupos de acordo com a faixa etária: um a três anos (GI), quatro a sete anos (GII), oito a 11 anos (GIII) e 12 anos ou mais (GIV). Foram mensuradas a amplitude pico a pico (pico da onda-a até o pico da onda-b) e o tempo de culminação da onda-b na resposta de bastonetes, máxima resposta e resposta de cones. Cães com respostas atenuadas ou extintas foram excluídos deste trabalho. Observou-se diminuição das amplitudes das três respostas quando se comparou GI com os demais grupos. Houve aumento do tempo de culminação da onda-b na comparação da resposta de bastonetes de GI com os outros grupos. O tempo de culminação da onda-b na máxima resposta e resposta de cones manteve-se praticamente inalterado nos quatro grupos testados. Concluiu-se que houve alteração dependente de idade nos parâmetros eletrorretinográficos, com diminuição da amplitude na resposta de bastonetes, máxima resposta e resposta de cones, enquanto que, no tempo de culminação da onda-b, apenas a resposta de bastonetes foi estatisticamente significante nos animais submetidos ao mesmo protocolo na execução do ERG.

Functional Changes in the Retina during and after Acute Intraocular Pressure Elevation in Mice

To examine retinal function using the full-field electroretinogram (ERG) during and after acute intraocular pressure (IOP) elevation in wild-type mice. IOP was elevated by anterior chamber cannulation in wild-type C57/BL6 mice. The pressure-function relationship was determined by IOP elevation in steps from baseline to 80 mm Hg. The rate of functional recovery was assessed for 60 minutes after an IOP spike of 50 mm Hg for 30 minutes. During and immediately after IOP elevation, scotopic ERG signals were recorded in response to dim and bright flashes (-4.54, -2.23, and 0.34 log cd x s x m(-2)) and analyzed for photoreceptoral (a-wave), ON-bipolar (b-wave), oscillatory potentials (OPs), and scotopic threshold responses (positive [p]STR/negative [n] STR). A full ERG protocol was collected 2 days before and 7 days after the single 50-mm Hg IOP spike. The pSTR was most sensitive to IOP elevation with 50% amplitude loss (mu) at 41 mm Hg (mu, 95% confidence limits (CL): 37.7, 45.6) followed by nSTR at 45 mm Hg (95% CL: 41.0, 49.1). pSTR was significantly more sensitive than the b-wave (95% CL: 41.4, 49.1), a-wave (95% CL: 47.6, 55.3), and OPs (95% CL: 49.6, 59.2). pSTR showed slower recovery immediately after the 50 mm Hg spike compared with the b-wave (P = 0.02). One week after the 50-mm Hg spike, pSTR (-30% +/- 6%, P < 0.001) and OP (-27% +/- 2%, P < 0.001) amplitudes were reduced, whereas other components were unaffected. The STR in mice is more sensitive to acute IOP elevation and recovers slower than other ERG components. Reduction in pSTR and OP amplitude at 1 week suggests persistent impairment of inner retinal function can occur after a single IOP spike.

The ERG in drug development: translation from animal models to human

Drug development is a long and complex process with a low likelihood of success. In order to allocate resources to compounds that will provide significant improvement to patients, it is imperative to develop measures that are predictive of clinical efficacy and safety. In the development of therapies for diseases of the retina, the electroretinogram (ERG) is a technique that is well suited to provide such information. As a functional measure, the ERG is more closely related to accepted behavioral endpoints than structural measures such as optical coherence tomography, and fluorescein angiography. Unlike most other measures of visual function, the ERG is easily obtained in animal models. These characteristics make the ERG a good biomarker to suggest the safety and efficacy of new treatments of retinal diseases. The ERG is also a sensitive measure of toxic effects of systemic therapies on the retina. In 2007, I organized a symposium entitled ERG in Drug Development: Translation from Animal Models to Human, held in Hyderabad, India as a part of the 45th ISCEV Symposium. The papers that follow summarize some of the presentations made at this symposium. Ido Perlman gave the keynote address at the Drug Development symposium, summarizing his elegant work using the ERG to detect and understand toxic effects of compounds on the retina. In this paper, Dr. Perlman also shows how these studies can help us understand the normal functioning of the retina. Jonathan Lyons and Matt Severns extend their published work on the use of the mfERG and ring ratios to detect toxic effects of hydroxychloroquine on the retinae of patients on long-term high-dose therapy. Pierre LaChapelle et al. show the use of the ERG in animal models of retinopathy of prematurity, and Ann Fulton et al. summarize their use of the ERG in translational research on degenerative and ischemic retinal diseases in children. Finally, Christina Gerth provides an overview of the use of the ERG in agerelated macular degeneration and the potential role of the mfERG in monitoring therapeutic interventions in this disease. Other presentations at the symposium were by Mathias Seeliger on the use of the ERG in animal models of retinal degenerative diseases, Laura Frishman on the use of various ERG techniques in preclinical models of glaucoma, Michael Bach on use of the pattern ERG in longitudinal studies of patients with ocular hypertension, and Eberhardt Zrenner emphasizing the need for standardized ERG protocols for use in multi-center clinical trials. Abstracts of all presentations in this special symposium can be found in Documenta Ophthalmologica 2007;115:21–26.

Reappraisal of a short-wavelength-sensitive (S-cone) recording technique in routine clinical electroretinography.

The recording of blue cone (S-cone) responses as described by Gouras and MacKay was slightly modified and incorporated into our routine ganzfeld electroretinogram protocol. We found a mean S-cone amplitude of 5.0 microV (range 2.9-6.9 microV) and a mean S-cone implicit time of 41.5 msec (range 40-46 msec). Separation between the combined red and green cone (L-M-cone) response and the S-cone response was obtained with blue flash stimuli on a yellow adapting background.