The photopic negative response of the Light-adapted 3.0 ERG in clinical settings

Associations of light-adapted electroretinogram in paediatric amblyopia

PURPOSE

The aim of this study was to investigate changes in the light-adapted (LA) electroretinogram (ERG) associated with paediatric amblyopia.

METHOD

A total of 220 eyes from 81 postoperative paediatric cataract patients and 29 healthy children were enrolled in four groups, namely controls, unilaterally amblyopic eyes, non-amblyopic fellow eyes and bilaterally affected eyes. Differences in LA ERG variables (peak time and amplitude of a- and b-waves and photopic negative response [PhNR]) were compared across groups, as well as their associations with visual acuity and changes in axial length.

RESULTS

The peak time of both the a-wave (p < 0.001) and b-wave (p < 0.001), as well as the amplitude of the b-wave (p < 0.001) and the PhNR (p = 0.04) differed significantly across groups. Compared to controls, affected eyes in both unilateral and bilateral groups showed significantly lower b-wave amplitude and longer a- and b-wave peak times (p < 0.008, Bonferroni-corrected). Additionally, fellow eyes in the unilateral group exhibited significantly longer b-wave peak times (p = 0.008). For all eyes, poorer visual acuity was associated with a longer peak time for both the a- (p = 0.006) and b-waves (p = 0.003), as well as lower amplitudes of the b-wave (p = 0.006) and PhNR (p = 0.02).

CONCLUSIONS

Changes in LA ERG components suggest alteration of retinal physiology in deprivation amblyopia. Thus, the LA ERG may provide additional information to help understand the mechanisms underlying deprivation amblyopia.

Impact of Myopia on the Utility of the Photopic Negative Response Ratio for Glaucoma Assessment

Background: The objective assessment of visual function is crucial in glaucoma management, highlighting the importance of electroretinography (ERG). This study investigates the diagnostic performance of photopic negative response (PhNR) amplitude and the normalized PhNR/b-wave ratio in diagnosing glaucoma, focusing on the impact of myopia. Methods: Ninety-one glaucoma patients and 19 glaucoma suspects were included, defining myopia as axial length (AL) > 24 mm or > 25 mm. Full-field photopic ERG used a red stimulus on a blue background. Results: Myopic glaucoma patients showed a higher PhNR/b-wave ratio than non-myopic patients (p = 0.023). AL negatively correlated with b-wave amplitude (r = -0.239, p = 0.012). PhNR amplitude demonstrated an area under the receiver operating characteristic curve (AUC) of 0.661 (p = 0.028) overall and was less effective in the myopic subgroup (AUC = 0.574, p = 0.082). The diagnostic performance of the PhNR/b-wave ratio did not achieve statistical significance in either the total group (AUC = 0.616, p = 0.114) or the myopic subgroup (AUC = 0.574, p = 0.332). Conclusions: Standardization using the PhNR/b-wave ratio did not enhance diagnostic accuracy over PhNR amplitude, particularly in myopic patients, underscoring the need for careful interpretation in myopia and further research to optimize electrophysiological diagnostics.

Association analyses of the measurements of the photopic negative response evoked by two ISCEV protocols

PURPOSE

To perform association analyses between the measurements of photopic negative response (PhNR) evoked by two ISCEV protocols.

METHODS

A total of 172 eyes from 72 post-operative pediatric cataract patients and 24 healthy children were enrolled. The amplitude and peak time of PhNR were analyzed in three eye groups, 1. healthy controls; 2. fellow eyes of unilaterally affected patients; 3. affected eyes. PhNR responses were measured with skin-electrodes and evoked by the ISCEV standard protocols of PhNR and light-adapted 3.0, referred to as PhNR1 and PhNR2. The correlation coefficients between PhNR1 and PhNR2 measurements were calculated. The generalized estimating equation (GEE) model of PhNR1, with PhNR2 as a predictor, was evaluated after adjusting for correlation between paired eyes.

RESULTS

Both the amplitude (P = 0.025) and the peak time (P = 0.036) of PhNR1 showed a significant difference among the three eye groups, which was not observed in PhNR2. The four correlation coefficients (Pearson, Intraclass, Lin's and Kendall's) between z-score transformed PhNR1 and PhNR2 measurements were generally moderate: 0.52, 0.52, 0.52, 0.36 for amplitude (P < 0.001), and 0.57, 0.57, 0.57, 0.36 for peak time (P < 0.001). The amplitude of PhNR1 cannot be precisely predicted by PhNR2, with a mean absolute percentage error (MAPE) of 36.7%, while the peak time of PhNR1 can be precisely predicted with a MAPE of 3.9%.

CONCLUSIONS

PhNR1 appears to be a more sensitive measure than PhNR2 for detecting eye group differences. Further research is needed to confirm this and explore its clinical applications. PhNR1 may not be entirely replaced by PhNR2 due to moderate correlation and low prediction precision in amplitude.

The Electroretinogram I-Wave, a Component Originating in the Retinal OFF-Pathway, Associates With a Myopia Genetic Risk Polymorphism

Purpose

One of the strongest genetic associations with myopia is near the GJD2 gene. Recently, this locus was associated with cone-driven electroretinograms (ERGs), with findings highlighting OFF pathway signals specifically. The ERG i-wave is thought to originate in retinal OFF pathways. We explored this component and tested the hypothesis that it would be associated with the myopia risk locus.

Methods

International standard LA3 ERGs, recorded with conductive fiber electrodes, were analyzed, first from patients with rare monogenic deficits impairing the ON pathway, or both ON and OFF pathways, to explore effects on the i-wave. Responses were then analyzed from adult participants from the TwinsUK cohort: i-wave amplitudes were measured by two investigators independently, blinded to genotype at the GJD2 locus. We investigated the association between i-wave amplitude and allelic identity at this locus, adjusting for age, sex, and familial relatedness.

Results

Patient recordings showed the i-wave persisted in the absence of ON pathway signals, but was abolished when both ON and OFF pathways were impaired. For TwinsUK participants, recordings and genotypes were available in 184 individuals (95% female participants; mean standard deviation [SD] age, 64.1 [9.7] years). Mean (SD) i-wave amplitude was 14.5 (SD = 6.5) microvolts. Allelic dosage at the risk locus was significantly associated with i-wave amplitude (P = 0.027).

Conclusions

Patient ERGs were consistent with the i-wave arising from cone-driven OFF pathways. Amplitudes associated significantly with allelic dosage at the myopia risk locus, supporting the importance of cone-driven signaling in myopia development and further highlighting relevance of the OFF pathway in relation to this locus.

Effects of Acute High-Altitude Exposure on Morphology and Function of Retinal Ganglion Cell in Mice

Purpose

High altitude retinopathy (HAR) is a retinal functional disorder caused by inadequate adaptation after exposure to high altitude. However, the cellular and molecular mechanisms underlying retinal dysfunction remain elusive. Retinal ganglion cell (RGC) injury is the most important pathological basis for most retinal and optic nerve diseases. Studies focusing on RGC injury after high-altitude exposure (HAE) are scanty. Therefore, the present study sought to explore both functional and morphological alterations of RGCs after HAE.

Methods

A mouse model of acute hypobaric hypoxia was established by mimicking the conditions of a high altitude of 5000 m. After HAE for 2, 4, 6, 10, 24, and 72 hours, the functional and morphological alterations of RGCs were assessed using retinal hematoxylin and eosin (H&E) sections, retinal whole mounts, transmission electron microscopy (TEM), and the photopic negative response (PhNR) of the electroretinogram.

Results

Compared with the control group, the thickness of the ganglion cell layer and retinal nerve fiber layer increased significantly, RGC loss remained significant, and the amplitudes of a-wave, b-wave, and PhNR were significantly reduced after HAE. In addition, RGCs and their axons exhibited an abnormal ultrastructure after HAE, including nuclear membrane abnormalities, uneven distribution of chromatin in the nucleus, decreased cytoplasmic electron density, widening and vacuolization of the gap between axons, loosening and disorder of myelin sheath structure, widening of the gap between myelin sheath and axon membrane, decreased axoplasmic density, unclear microtubule and nerve fiber structure, and abnormal mitochondrial structure (mostly swollen, with widened membrane gaps and reduced cristae and vacuolization).

Conclusions

The study findings confirm that the morphology and function of RGCs are damaged after HAE. These findings lay the foundation for further study of the specific molecular mechanisms of HAR and promote the effective prevention.

Intereye structure-function relationship using photopic negative response in patients with glaucoma or glaucoma suspect

We evaluated the intereye structure–function relationship in glaucoma patients using photopic negative response in electroretinogram analysis. Patients with confirmed glaucoma (36 eyes, 36 patients) or suspected glaucoma (19 eyes, 19 patients) were included in this study. Electroretinogram (RETI-scan) was performed with red stimulus on blue background. Intereye comparison for 55 patients was performed between better eyes and worse eyes, which were divided based on average retinal nerve fiber layer (RNFL) thickness measured using spectral-domain optical coherence tomography. In the intereye analysis, PhNR amplitude was lower in worse eyes than in better eyes (P < 0.001). The intereye difference in PhNR amplitude was significantly correlated with intereye difference in average RNFL, as well as average or minimum ganglion cell-inner plexiform layer (GCIPL) thickness (P = 0.006, 0.044, 0.001). In patients with mean deviation ≥ − 6 dB of worse eyes, the intereye difference in PhNR amplitude was significantly associated with intereye difference in average RNFL thickness or minimum GCIPL thickness (P = 0.037, 0.007), but significant correlation was not found between mean sensitivity of visual field tests and structural parameters. In conclusion, PhNR performed well with regard to intereye structure–function association in glaucoma patients, especially at the early stage.

Prediction of glaucoma severity using parameters from the electroretinogram

Glaucoma is an optic neuropathy that results in the progressive loss of retinal ganglion cells (RGCs), which are known to exhibit functional changes prior to cell loss. The electroretinogram (ERG) is a method that enables an objective assessment of retinal function, and the photopic negative response (PhNR) has conventionally been used to provide a measure of RGC function. This study sought to examine if additional parameters from the ERG (amplitudes of the a-, b-, i-wave, as well the trough between the b- and i-wave), a multivariate adaptive regression splines (MARS; a non-linear) model and achromatic stimuli could better predict glaucoma severity in 103 eyes of 55 individuals with glaucoma. Glaucoma severity was determined using standard automated perimetry and optical coherence tomography imaging. ERGs targeting the PhNR were recorded with a chromatic (red-on-blue) and achromatic (white-on-white) stimulus with the same luminance. Linear and MARS models were fitted to predict glaucoma severity using the PhNR only or all ERG markers, derived from chromatic and achromatic stimuli. Use of all ERG markers predicted glaucoma severity significantly better than the PhNR alone (P ≤ 0.02), and the MARS performed better than linear models when using all markers (P = 0.01), but there was no significant difference between the achromatic and chromatic stimulus models. This study shows that there is more information present in the photopic ERG beyond the conventional PhNR measure in characterizing RGC function.

Effect of spatial averaging on the amplitude ring ratio in multifocal electroretinography

PURPOSE

The purpose of this study was to evaluate the effect of spatial averaging on the multifocal electroretinography (mfERG) amplitude ring ratios used in screening for hydroxychloroquine (HCQ) toxicity.

METHODS

This was a retrospective review of the records of patients screened for HCQ retinopathy at the USF Eye Institute (University of South Florida) during the period of 2015-2020. Patients were tested binocularly with Diagnosys mfERG system (Diagnosys LLC, Lowell, MA). Only the records of patients referred internally were used. The effects of the lowest level (level 1, or 8%) of spatial averaging on the P1 amplitude ring ratios used for screening of HCQ maculopathy: R1/R2, R2/R5, R5/R3 and R5/R4, were evaluated.

RESULTS

The records of 40 patients (4 males, 36 females) aged 54.4 ± 14.1 years were selected for analysis. The use of spatial averaging had a significant effect on P1 amplitudes, and on the ring ratios and this effect was correlated with the magnitude of the amplitudes and the ratios. Spatial averaging diminished P1 amplitude significantly in ring 1 (p < 0.0001) and increased it slightly in ring 4 (p < 0.05), while it had no effect on the amplitude of the other three rings. Although as a group spatial averaging had a moderate effect on the R1/R2 ratio (~ -15%), on an individual basis the range was wide, from -36 to 43%. The effect on the other ring ratios was similar: The average group effect was ~ -5%, ~ -3.4% and ~ -4% for R2/R5, R5/R3 and R5/R4 ratios, but individual effects ranged from 0.18% to -27.3%, 0.9% to -14.2% and 0.9% to -26.2%, respectively.

CONCLUSIONS

For all ring ratios used in this analysis, spatial averaging has a substantial effect on the ring ratio, which could affect the interpretation of the results. Therefore, use of spatial averaging should be avoided when analyzing mfERG results for HCQ screening.

Relationship between stimulus size and different components of the electroretinogram (ERG) elicited by flashed stimuli

PURPOSE

To investigate how light stimulus conditions of varying spatial sizes affect components of the flash and long-flash electroretinogram (ERG) in normal subjects.

METHOD

Three stimulus conditions were generated by a Ganzfeld stimulator: a white flash on white background (WoW), a red flash on a blue background (RoB) and an L+M-cone isolating on-off (long flash) stimulus (Cone Iso). ERGs were recorded from six subjects (5 M, 1 F) with DTL electrodes to full-field (FF), 70°, 60°, 50°, 40°, 30° and 20° diameter circular stimuli. Amplitudes and peak times for a-, b-, d- and i-wave, and PhNR were examined. PhNR amplitudes were estimated in two different ways: from baseline (fB) and from preceding b-wave peak (fP).

RESULTS

With decreasing stimulus size, amplitudes for all ERG waveform components attenuated and peak times increased, although the effect varied across different components. An exponential fit described the relationship between amplitudes and size of stimulated retinal area well for most components and conditions (R²= 0.75-0.99), except for PhNR(fB) (R²= - 0.16-0.88). For peak times, an exponential decay function also fitted the data well (R²= 0.81-0.97), except in a few cases where the exponential constant was too small and a linear regression function was applied instead (a-wave Cone Iso, b- and i-wave WoW). The exponential constants for RoB amplitudes (b-wave, PhNR(fB), PhNR(fP)) were larger compared to their counterparts under WoW (p < 0.05), while there was no difference between the constants for a-wave amplitudes and peak times and for PhNR peak times. The exponential constants of amplitudes vs. area under WoW and Cone Iso were remarkably similar, while under RoB PhNR(fB) showed larger constants compared to either a- or b-wave (p < 0.05).

CONCLUSION

ERG components change in a predictable way with stimulus size and spectral characteristics of the stimulus under these conditions. This predictability could allow a modified version of these sets of stimuli to be tested for clinical applicability.

The influence of mild cataract on ISCEV standard electroretinogram recorded from mydriatic eyes

PURPOSE

To investigate the effect of mild cataract and its surgery on the ISCEV standard electroretinogram (ERG) by comparing pre- and postoperative ERGs elicited from fully dilated eyes.

METHODS

Twenty-two patients participated. Each eye had cataract of grade 2 according to Emery-Little classification. None had complications during and after phacoemulsification and intraocular lens implantation. According to the ISCEV standard, pre- and 1-week postoperative full-field ERGs, dark adapted (DA) 0.01, DA 3, DA 3 oscillatory potentials (OPs), DA 10, and light adapted (LA) 3, and LA 3 flicker, were elicited from fully dilated eyes using skin electrodes. Photopic negative response (PhNR) 1 amplitude was measured from the baseline to the trough before the i-wave in the LA 3 ERG waveform. Statistical analysis was performed using SigmaPlot version 11.0 (Systat Software, Inc., San Jose, CA, USA). Pre- and postoperative data were compared using a paired t-test. Non-normally distributed data were evaluated using the Wilcoxon signed rank test.

RESULTS

The pre- and 1-week postoperative amplitudes in each component were as follows: DA 0.01: 48.4 ± 19.5 μV and 57.1 ± 20.0 μV (p = 0.002), a-wave of DA3: 51.5 ± 14.8 μV and 58.3 ± 17.3 μV (p = 0.003), b-wave of DA3: 88.3 ± 27.5 μV and 101.5 ± 29.7 μV (p = 0.003), DA 3 ΣOPs (sum of DA 3 OP1, OP2, and OP3 amplitude): 30.7 ± 16.3 μV and 37.1 ± 21.9 μV (p < 0.001), a-wave of DA 10: 65.5 ± 18.8 μV and 74.2 ± 19.5 μV (p < 0.001), b-wave of DA 10: 95.5 ± 29.6 μV and 111.1 ± 29.9 μV (p < 0.001), a-wave of LA 3: 7.2 ± 2.6 μV and 8.2 ± 2.2 μV (p = 0.025), b-wave of LA 3: 30.6 ± 12.9 μV and 35.3 ± 12.7 μV (p = 0.003), PhNR1: 5.8 ± 2.5 μV and 5.5 ± 2.6 μV (p = 0.562), and LA 3 flicker: 25.4 ± 8.9 μV and 27.8 ± 8.6 μV (p = 0.039), respectively. The implicit time of all the components did not reveal significant differences before and after surgery.

CONCLUSIONS

Cataractous lens removal and intraocular lens implantation may influence ISCEV standard ERGs, even if the cataract is relatively mild.

Photopic negative response using a handheld mini-ganzfeld stimulator in healthy adults: normative values, intra- and inter-session variability

PURPOSE

To determine normative values, intra- and inter-session variability for a range of parameters derived from the photopic negative response (PhNR) using a handheld mini-Ganzfeld stimulator in healthy normal adults.

METHODS

Light-adapted flash full-field electroretinograms (ERGs) were recorded from healthy individuals with no visual complaints, visual acuity equal to or better than 0.0 logMAR (20/20 Snellen), and negative family history for visual diseases. ERGs were recorded from both eyes using a DTL^® type fiber electrode after dilation of the pupils with instillation of 1 drop of tropicamide eye drops (1%). The full-field PhNR stimulus conditions were produced by a LED-based ColorBurst™ (Diagnosys LLC, Lowell, MA, USA) handheld stimulator. Red flashes of 1, 5 and 7 cd.s/m² on a blue background of 10 cd/m² were presented. A-wave, b-wave and PhNR amplitude (determined by both baseline to trough-BT and peak to trough-PT) and peak times were analyzed. Normal limits were determined as 5% percentile for amplitudes and 95% percentile for latencies. Intra- and inter-session variability were assessed with Wilcoxon signed-rank test, intraclass correlation coefficient (ICC) and the coefficient of variability (COV).

RESULTS

Normative limits for PhNR amplitude (µV) using 1, 5 and 7 cd.s./m2 stimuli were, respectively: 20.81; 18.06 and 19.60 for BT and 69.11; 77.98; 76.51 for PT. Peak times (ms) normative limits for 1, 5 and 7 cd.s/m2 intensities were, respectively, 65.98; 78.20 and 77.96. Overall, intra-session variability assessed by coefficients of variation ranged from 1.35 to 10.28%. Inter-session variability disclosed significant intraclass correlation values for all PhNR parameters only for 1 cd.s/m2 stimuli.

CONCLUSIONS

The normative values provided by this study are clinically helpful in the diagnosis of inner retinal disorders, especially those affecting retinal ganglion cells such as glaucoma and other optic neuropathies. Further studies, including a larger sample with variable age range would extend the validity of the current results.

Developments in non-invasive visual electrophysiology

To study the physiology of the primate visual system, non-invasive electrophysiological techniques are of major importance. Two main techniques are available: the electroretinogram (ERG), a mass potential originating in the retina, and the visual evoked potential (VEP), which reflects activity in the primary visual cortex. In this overview, the history and the state of the art of these techniques are briefly presented as an introduction to the special issue "New Developments in non-invasive visual electrophysiology". The overview and the special issue can be used as the starting point for exciting new developments in the electrophysiology of primate and mammalian vision.