Electroretinogram Responses Research Articles

Electroretinographic examinations of the crew members of the 8-month international experiment SIRIUS 20/21

Before and after the 8-month international experiment SIRIUS 20/21, a complex of electrophysiological testing of the visual system was performed, including registration of standard photopic electroretinograms (ERG), flicker ERG response on flickering with a frequency of 8.3, 10, 12 and 24 Hz, photopic negative response, and pattern-ERG. The aim of the work was an objective assessment of changes in the functional activity of retinal neurons in ground station crew members associated with long-term isolation and the influence of a complex of stress factors. The results obtained indicate a moderate activation of the bioelectrical activity of photoreceptors and bipolar cells and a slight decrease in the function of retinal ganglion cells after isolation experiment. The revealed changes may reflect the adaptation of the visual sensory system of the testers to physical and psycho-emotional stress in the experimental conditions. Further study of the specifics of changes in electroretinographic markers with a longer duration of the experiment is necessary to expand the understanding of stress resistance and adaptation of the visual system during prolonged exposure to extreme environmental conditions.

Mercury intoxication and ophthalmic involvement: An update review.

Human intoxication after mercury exposure is a rare condition that can cause severe damage to the central nervous, respiratory, cardiovascular, renal, gastrointestinal, skin, and visual systems and represents a major public health concern. Ophthalmic involvement includes impaired function of the extraocular muscles and the eyelids, as well as structural changes in the ocular surface, lens, retina, and optic nerve causing a potential irreversible damage to the visual system. Although, there are many pathways for poisoning depending on the mercury form, it has been suggested that tissue distribution does not differ in experimental animals when administered as mercury vapor, organic mercury, or inorganic mercury. Additionally, visual function alterations regarding central visual acuity, color discrimination, contrast sensitivity, visual field and electroretinogram responses have also been described widely. Nevertheless, there is still controversy about whether visual manifestations occur secondary to brain damage or as a direct affectation, and which ocular structure is primarily affected. Despite the use of some imaging techniques such as in vivo confocal microscopy of the cornea, optical coherence tomography (OCT) of the retina and optic nerve, and functional tests such as electroretinography has helped to solve in part this debate, further studies incorporating other imaging modalities such as autofluorescence, OCT angiography or adaptive optics retinal imaging are needed. This review aims to summarize the published structural and functional alterations found in the visual system of patients suffering from mercury intoxication.

Long-term blue light rearing does not affect in vivo retinal function in young rhesus monkeys.

Exposure to blue light is thought to be harmful to the retina. The purpose of this study was to determine the effects of long-term exposure to narrowband blue light on retinal function in rhesus monkeys. Young rhesus monkeys were reared under short-wavelength "blue" light (n = 7; 465nm, 183 ± 28lx) on a 12-h light/dark cycle starting at 26 ± 2days of age. Age-matched control monkeys were reared under broadband "white" light (n = 8; 504 ± 168lx). Light- and dark-adapted full-field flash electroretinograms (ERGs) were recorded at 330 ± 9days of age. Photopic stimuli were brief red flashes (0.044-5.68cd.s/m2) on a rod-saturating blue background and the International Society for Clinical Electrophysiology of Vision (ISCEV) standard 3.0 white flash on a 30cd/m2 white background. Monkeys were dark adapted for 20min and scotopic stimuli were ISCEV standard white flashes of 0.01, 3.0, and 10cd.s/m2. A-wave, b-wave, and photopic negative response (PhNR) amplitudes were measured. Light-adapted ERGs in young monkeys were compared to ERGs in adult monkeys reared in white light (n = 10; 4.91 ± 0.88years of age). For red flashes on a blue background, there were no significant differences in a-wave (P = 0.46), b-wave (P = 0.75), and PhNR amplitudes (P = 0.94) between white light and blue light reared monkeys for all stimulus energies. ISCEV standard light- and dark-adapted a- and b-wave amplitudes were not significantly different between groups (P > 0.05 for all). There were no significant differences in a- and b-wave implicit times between groups for all ISCEV standard stimuli (P > 0.05 for all). PhNR amplitudes of young monkeys were significantly smaller compared to adult monkeys for all stimulus energies (P < 0.05 for all). There were no significant differences in a-wave (P = 0.19) and b-wave (P = 0.17) amplitudes between young and adult white light reared monkeys. Long-term exposure to narrowband blue light did not affect photopic or scotopic ERG responses in young monkeys. Findings suggest that exposure to 12h of daily blue light for approximately 10months does not result in altered retinal function.

Biphasic expression of thyroid hormone receptor TRβ1 in mammalian retina and anterior ocular tissues.

The retina is increasingly recognized as a target of thyroid hormone. We previously reported critical functions for thyroid hormone receptor TRβ2, encoded by Thrb, in cones, the photoreceptors that mediate color vision. TRβ1, another Thrb receptor isoform, is widely expressed in other tissues but little studied in the retina. Here, we investigate these N-terminal isoforms by RNA-sequencing analysis and reveal a striking biphasic profile for TRβ1 in mouse and human retina. In contrast to the early TRβ2 peak, TRβ1 peaks later during retinal maturation or later differentiation of human retinal organoids. This switch in receptor expression profiles was confirmed using lacZ reporter mice. TRβ1 localized in cones, amacrine cells and ganglion cells in contrast to the restricted expression of TRβ2 in cones. Intriguingly, TRβ1 was also detected in the retinal pigmented epithelium and in anterior structures in the ciliary margin zone, ciliary body and iris, suggesting novel functions in non-retinal eye tissues. Although TRβ1 was detected in cones, TRβ1-knockout mice displayed only minor changes in opsin photopigment expression and normal electroretinogram responses. Our results suggest that strikingly different temporal and cell-specific controls over TRβ1 and TRβ2 expression may underlie thyroid hormone actions in a range of ocular cell types. The TRβ1 expression pattern suggests novel functions in retinal and non-neural ocular tissues.

Vision rescue via unconstrained in vivo prime editing in degenerating neural retinas.

Retinitis pigmentosa (RP) is an inherited retinal dystrophy causing progressive and irreversible loss of retinal photoreceptors. Here, we developed a genome-editing tool characterized by the versatility of prime editors (PEs) and unconstrained PAM requirement of a SpCas9 variant (SpRY), referred to as PESpRY. The diseased retinas of Pde6b-associated RP mouse model were transduced via a dual AAV system packaging PESpRY for the in vivo genome editing through a non-NGG PAM (GTG). The progressing cell loss was reversed once the mutation was corrected, leading to substantial rescue of photoreceptors and production of functional PDE6β. The treated mice exhibited significant responses in electroretinogram and displayed good performance in both passive and active avoidance tests. Moreover, they presented an apparent improvement in visual stimuli-driven optomotor responses and efficiently completed visually guided water-maze tasks. Together, our study provides convincing evidence for the prevention of vision loss caused by RP-associated gene mutations via unconstrained in vivo prime editing in the degenerating retinas.

Association between relative peripheral refraction and corresponding electro-retinal signals.

Considering the potential role of the peripheral retina in refractive development and giventhat peripheral refraction varies significantly with increasing eccentricity from the fovea, we investigated the association between relative peripheral refraction (RPR) and corresponding relative peripheral multifocal electroretinogram (mfERG) responses (electro-retinal signals) from the central to the peripheral retina in young adults. Central and peripheral refraction using an open-field autorefractor and mfERG responses using an electrophysiology stimulator were recorded from the right eyes of 17 non-myopes and 24 myopes aged 20-27 years. The relative mfERG N1, P1 and N2 components (amplitude density and implicit time) of a mfERG waveform were compared with the corresponding RPR measurements at the best-matched eccentricities along the principal meridians, that isatthe fovea (0°), horizontal (±5°, ±10° and ± 25°) and vertical meridians (±10° and ± 15°). The mean absolute mfERG N1, P1 and N2 amplitude densities (nV/deg2 ) were maximum at the fovea in both non-myopes (N1: 57.29 ± 14.70 nV/deg2 , P1: 106.29 ± 24.46 nV/deg2 , N2: 116.41 ± 27.96 nV/deg2 ) and myopes (N1: 56.25 ± 15.79 nV/deg2 , P1: 100.79 ± 30.81 nV/deg2 , N2: 105.75 ± 37.91 nV/deg2 ), which significantly reduced with increasing retinal eccentricity (p < 0.01). No significant association was reported between the RPR and corresponding relative mfERG amplitudes at each retinal eccentricity (overall Pearson's correlation, r=-0.25 to 0.26, p ≥ 0.09). In addition, the presence of relative peripheral myopia or hyperopia at extreme peripheral retinal eccentricities did not differentially influence the corresponding relative peripheral mfERG amplitudes (p ≥ 0.24). Relative peripheral mfERG signals are not associated with corresponding RPR in young adults. It is plausible that the electro-retinal signals may respond to the presence of absolute hyperopia (and not relative peripheral hyperopia), which requires further investigation.

Retinal Dysfunction in a Mouse Model of HCN1 Genetic Epilepsy.

Pathogenic variants in HCN1 are associated with a range of epilepsy syndromes including a developmental and epileptic encephalopathy. The recurrent de novo HCN1 pathogenic variant (M305L) results in a cation leak, allowing the flux of excitatory ions at potentials where the wild-type channels are closed. The Hcn1M294L mouse recapitulates patient seizure and behavioral phenotypes. As HCN1 channels are highly expressed in rod and cone photoreceptor inner segments, where they shape the light response, mutated channels are likely to impact visual function. Electroretinogram (ERG) recordings from male and female mice Hcn1M294L mice revealed a significant decrease in the photoreceptor sensitivity to light, as well as attenuated bipolar cell (P2) and retinal ganglion cell responses. Hcn1M294L mice also showed attenuated ERG responses to flickering lights. ERG abnormalities are consistent with the response recorded from a single female human subject. There was no impact of the variant on the structure or expression of the Hcn1 protein in the retina. In silico modeling of photoreceptors revealed that the mutated HCN1 channel dramatically reduced light-induced hyperpolarization, resulting in more Ca2+ flux during the response when compared with the wild-type situation. We propose that the light-induced change in glutamate release from photoreceptors during a stimulus will be diminished, significantly blunting the dynamic range of this response. Our data highlight the importance of HCN1 channels to retinal function and suggest that patients with HCN1 pathogenic variants are likely to have a dramatically reduced sensitivity to light and a limited ability to process temporal information.SIGNIFICANCE STATEMENT Pathogenic variants in HCN1 are emerging as an important cause of catastrophic epilepsy. HCN1 channels are ubiquitously expressed throughout the body, including the retina. Electroretinogram recordings from a mouse model of HCN1 genetic epilepsy showed a marked decrease in the photoreceptor sensitivity to light and a reduced ability to respond to high rates of light flicker. No morphologic deficits were noted. Simulation data suggest that the mutated HCN1 channel blunts light-induced hyperpolarization and consequently limits the dynamic range of this response. Our results provide insights into the role HCN1 channels play in retinal function as well as highlighting the need to consider retinal dysfunction in disease caused by HCN1 variants. The characteristic changes in the electroretinogram open the possibility of using this tool as a biomarker for this HCN1 epilepsy variant and to facilitate development of treatments.

X-Linked Retinoschisis.

X-linked retinoschisis (XLRS) is an inherited vitreoretinal dystrophy causing visual impairment in males starting at a young age with an estimated prevalence of 1:5000 to 1:25,000. The condition was first observed in two affected brothers by Josef Haas in 1898 and is clinically diagnosed by characteristic intraretinal cysts arranged in a petaloid "spoke-wheel" pattern centered in the macula. When clinical electroretinogram (ERG) testing began in the 1960s, XLRS was noted to have a characteristic reduction of the dark-adapted b-wave amplitude despite normal or usually nearly normal a-wave amplitudes, which became known as the "electronegative ERG response" of XLRS disease. The causative gene, RS1, was identified on the X-chromosome in 1997 and led to understanding the molecular and cellular basis of the condition, discerning the structure and function of the retinoschisin protein, and generating XLRS murine models. Along with parallel development of gene delivery vectors suitable for targeting retinal diseases, successful gene augmentation therapy was demonstrated by rescuing the XLRS phenotype in mouse. Two human phase I/II therapeutic XLRS gene augmentation studies were initiated; and although these did not yield definitive improvement in visual function, they gave significant new knowledge and experience, which positions the field for further near-term clinical testing with enhanced, next-generation gene therapy for XLRS patients.

Pre-stimulus bioelectrical activity in light-adapted ERG under blue versus white background.

To compare the baseline signal between two conditions used to generate the photopic negative response (PhNR) of the full-field electroretinogram (ERG): red flash on a blue background (RoB) and white flash on a white background (LA3). The secondary purpose is to identify how the level of pre-stimulus signal affects obtaining an unambiguous PhNR component. A retrospective chart review was conducted on four cohorts of patients undergoing routine ERG testing. In each group, LA3 was recorded the same way while RoB was generated differently using various luminances of red and blue light. The background bioelectrical activity 30ms before the flash was extracted, and the root mean square (RMS) of the signal was calculated and compared between RoB and LA3 using Wilcoxon test. Pre-stimulus noise was significantly higher under RoB stimulation versus LA3 in all four conditions for both right and left eyes (ratio RoB/LA3 RMS 1.70 and 1.57 respectively, p<0.033). There was also no significant difference between the RMS of either LA3 or RoB across protocols, indicating that the baseline noise across cohorts were comparable. Additionally, pre-stimulus noise was higher in signals where PhNR was not clearly identifiable as an ERG component versus signals with the presence of unambiguous PhNR component under RoB in all four groups for both eyes (p<0.05), whereas the difference under LA3 was less pronounced. Our study suggests that LA3 produces less background bioelectrical activity, likely due to decreased facial muscle activity. As it seems that the pre-stimulus signal level affects PhNR recordability, LA3 may also produce a better-quality signal compared to RoB. Therefore, until conditions for a comparable bioelectrical activity under RoB are established, we believe that LA3 should be considered at least as a supplementary method to evaluate retinal ganglion cell function by ERG.

Full-field stimulus threshold testing for evaluation of the retinal function in patients with inherited retinal dystrophy

Objective: To analyze the characteristics of full-field stimulus thresholds (FST) in patients with middle-and late-stage inherited retinal dystrophy (IRD), and to explore the feasibility of the FST test in evaluating the retinal function for IRD patients. Methods: It was a retrospective case series study. Twenty-eight patients with IRD whose full-field electroretinogram (ERG) results showed no electrical activity (20 patients) or a serious decrease in electrical activity (8 patients) were enrolled, including 17 males and 11 females, with a median age of 32 years. Ten normal controls were also enrolled. All eyes had a measurement of best corrected visual acuity (BCVA) and an ERG test. FST stimulated by red, blue and white lights were examined with an electrophysiological instrument. The decimal value of BCVA was converted to logarithm of the minimum angle of resolution. Data of the better eye of each participant were used for statistical analysis. Independent sample t-test was used to analyze the difference in FST among patients. Linear regression was used to analyze the correlation between FST, visual acuity and ERG amplitudes. Results: The BCVA of all eyes was 0.7±0.6. Under the stimulation of red, blue and white lights, the FST were(-27.0±7.1), (-47.4±12.2) and(-41.7±11.5) dB in the 8 eyes with decreased electrical activity, (-16.3±7.0), (-27.2±13.7) and(-23.5±12.5) dB in the 20 eyes with no electrical activity, and(-39.9±4.0), (-65.8±4.0) and(-58.5±3.4) dB in the 10 control eyes, respectively. The FST of IRD patients were higher than the normal controls. The FST with red, blue and white lasers in eyes with no electrical activity were higher than those with severely reduced electrical activity (t=-3.472, -3.506, -3.433; all P=0.002). The BCVA was not correlated with the FST under the red, blue and white light stimulation in eyes with a serious reduction in electrical activity (r=0.134, 0.011, 0.010; P=0.055, 0.601, 0.611). There was a linear correlation between the red light stimulus FST and the b-wave amplitude of flicker ERG response (r=-0.591, P=0.026), but there was no significant correlation between other amplitudes and FST. Conclusions: The FST test is a supplementary method to evaluate the retinal function of patients with middle-and late-stage IRD. It can quantitatively reflect the function of rod and cone cell system. As the retinal function of IRD patients decreases, the FST gradually increase.

Luminance white noise electroretinograms (wnERGs) in mice.

To record and analyse electroretinograms (ERGs) to luminance stimuli with white noise temporal profiles in mice. White noise stimuli are expected to keep the retina in a physiologically more natural state than, e.g., flashes. The influence of mean luminance (ML) was studied. Electroretinograms to luminance temporal white noise (TWN) modulation (wnERGs) were measured. The white noise stimuli contained all frequencies up to 20 Hz with equal amplitudes and random phases. Responses were recorded at 7 MLs between -0.7 and 1.2 log cd/m2. Impulse response functions (IRFs) were calculated by cross correlating the averaged white noise electroretinogram (wnERG) responses with the stimulus. Amplitudes and latencies of the initial trough and subsequent peak in the IRFs were measured at each ML. Fourier transforms of the IRFs resulted in modulation transfer functions (MTFs). wnERGs were averaged across different animals. They were measured twice and the responses at identical instances in the 1st and 2nd recordings were plotted against each other. The correlation coefficient (r 2 repr) of the linear regression quantified the reproducibility. The results of the first and second measurement were further averaged. To study the underlying ERG mechanisms, the ERG potentials at the different MLs were plotted against those at the lowest and highest ML. The correlation coefficients (r 2 ML) were used to quantify their similarities. The amplitudes of the initial (a-wave-like) trough of the IRFs increased with increasing ML. The following positive (b-wave-like) peak showed a minimum at -0.4 log cd/m2 above which there was a positive correlation between amplitude and ML. Their latencies decreased monotonously with increasing ML. In none of the IRFs, oscillatory potential (OP)-like components were observed. r 2 repr values were minimal at a ML of -0.1 log cd/m2, where the MTFs changed from low-pass to band-pass. r 2 ML values increased and decreased with increasing ML when correlated with responses obtained at the highest or the lowest ML, respectively. White noise electroretinograms can be reliably recorded in mice with luminance stimuli. IRFs resemble flash ERGs superficially, but they offer a novel procedure to study retinal physiology. New components can be described in the IRFs. The wnERGs are either rod- or cone-driven with little overlap.

Middle-Inner Macular Layers Dysfunction in a Case of Stellate Foveomacular Retinoschisis Detected by Abnormal Multifocal Photopic Negative Response Recordings.

We describe the macular morpho-functional assessment of a 65-year-old man affected by stellate nonhereditary idiopathic foveomacular retinoschisis (SNIFR), studied by visual field, SD-OCT, autofluorescence, full-field electroretinogram (ffERG), multifocal electroretinogram (mfERG) and multifocal Photopic Negative Response (mfPhNR) recordings. The typical presentation consists of the foveal appearance of radial cartwheel pattern for the splitting of the retinal layers at the level of the Henle fiber layer (HFL) and the outer plexiform layer (OPL), perfectly seen by Spectral Domain-Optical Coherence Tomography (SD-OCT). Despite a normal function of the outer retina of the peripheral and central retina evaluated by ffERG and mfERG respectively, we observed a reduced function of the retinal elements involved in the retinoschisis by recording mfPhNR that assesses mainly inner retina function (retinal ganglion cells and their axons). Therefore, it is likely that the observed impaired mfPhNR responses reflect the signaling defects derived from the delaminated middle retina and transmitted to the innermost retinal layers.

Compound Homozygous Rare Mutations in PLCE1 and HPS1 Genes Associated with Autosomal Recessive Retinitis Pigmentosa in Pakistani Families.

Retinitis pigmentosa (RP) belongs to pigmentary retinopathies, a generic name for all retinal dystrophies with a major phenotypical and genotypical variation, characterized by progressive reduction of photo-receptor functionality of the rod and cone. Global prevalence of RP is ~ 1/4000 and it can be inherited as autosomal dominant (adRP), autosomal recessive (arRP) or X- linked (xlRP). We designed this study to identify causative mutations in Pakistani families affected with arRP. In 2019, we recruited two unrelated Pakistani consanguineous families affected with progressive vision loss and night blindness from Punjab region. Clinical diagnosis confirmed the; bone spicule pigmentation of the retina, and an altered electroretinogram (EGR) response. Proband and healthy individual from each family were subjected for whole-exome sequencing (WES). Various computational tools were used to analyze the Next Generation Sequencing (NGS) data and to predict the pathogenicity of the identified mutations. WES data analysis highlighted two missense homozygous variants at position c.T1405A (p.S469T) in PLCE1 and c.T11C (p.V4A) in HPS1 genes in proband of both families. Healthy individuals of two families were tested negative for p.S469T and p.V4A mutations. The variant analysis study including molecular dynamic simulations predicted mutations as disease causing. Compound effect of mutations in rarely linked PLCE1 and HPS1 genes could also cause RP. This study highlights the potential application of WES for a rapid and precise molecular diagnosis for heterogeneous genetic diseases such as RP.

SPACR Encoded by IMPG1 Is Essential for Photoreceptor Survival by Interplaying between the Interphotoreceptor Matrix and the Retinal Pigment Epithelium.

Several pathogenic variants have been reported in the IMPG1 gene associated with the inherited retinal disorders vitelliform macular dystrophy (VMD) and retinitis pigmentosa (RP). IMPG1 and its paralog IMPG2 encode for two proteoglycans, SPACR and SPACRCAN, respectively, which are the main components of the interphotoreceptor matrix (IPM), the extracellular matrix surrounding the photoreceptor cells. To determine the role of SPACR in the pathological mechanisms leading to RP and VMD, we generated a knockout mouse model lacking Impg1, the mouse ortholog. Impg1-deficient mice show abnormal accumulation of autofluorescent deposits visible by fundus imaging and spectral-domain optical coherence tomography (SD-OCT) and attenuated electroretinogram responses from 9 months of age. Furthermore, SD-OCT of Impg1−/− mice shows a degeneration of the photoreceptor layer, and transmission electron microscopy shows a disruption of the IPM and the retinal pigment epithelial cells. The decrease in the concentration of the chromophore 11-cis-retinal supports this loss of photoreceptors. In conclusion, our results demonstrate the essential role of SPACR in maintaining photoreceptors. Impg1−/− mice provide a novel model for mechanistic investigations and the development of therapies for VMD and RP caused by IMPG1 pathogenic variants.

Mesenchymal stem cell-derived extracellular vesicles protect retina in a mouse model of retinitis pigmentosa by anti-inflammation through miR-146a-Nr4a3 axis

BackgroundRetinitis pigmentosa is a rod-cone degenerative disease that induces irreversible vision loss. This study probed the protective capacity of mesenchymal stem cell-derived small EVs (MSC-EVs) on the retinas of rd10 mice and the underlying mechanism.MethodsMSC-EVs were injected into the vitreous of rd10 mice at postnatal day 14 and P21; morphology and function were examined at P28. The mechanism of action was explored by using co-culture of photoreceptor cell line 661 W and microglia cell line BV2.ResultsTreatment with MSC-EVs increased the survival of photoreceptors and preserved their structure. Visual function, as reflected by optomotor and electroretinogram responses, was significantly enhanced in MSC-EVs-treated rd10 mice. Mechanistically, staining for Iba1, GFAP, F4/80, CD68 and CD206 showed that MSC-EVs suppressed the activation of microglial, Müller glial and macrophages. Furthermore, western blotting showed that the treatment inhibited the NF-κB pathway. RNA-seq and qPCR showed that MSC-EVs upregulated anti-inflammatory cytokines while downregulating pro-inflammatory cytokines. MSC-EVs application in vitro decreased the number of TUNEL-positive 661 W cells co-cultured with LPS-stimulated BV2, with similar impact on the cytokine expression as in vivo study. Genetic screening predicted miR-146a to be the downstream target of MSC-EVs, which was detected in MSC-EVs and upregulated in co-cultured 661 W cells and BV2 cells after MSC-EVs treatment. Upregulation of miR-146a by using its mimic decreased the expression of the transcription factor Nr4a3, and its downregulation inhibition promoted Nr4a3 expression in both 661 W and BV2 cells. Nr4a3 was further identified as the target gene of miR-146a by dual-luciferase assay. Furthermore, overexpressing miR-146a significantly decreased the expression of LPS-induced pro-inflammatory cytokines in BV2 cells.ConclusionsMSC-EVs delays retinal degeneration in rd10 mice mainly by its anti-inflammatory effect via the miR-146a-Nr4a3axis. Hence, MSC-EVs may be used in the treatment of neurodegenerative diseases.

Electroretinographic responses to luminance and cone-isolating white noise stimuli in macaques.

Electroretinograms (ERGs) are mass potentials with a retinal origin that can be measured non-invasively. They can provide information about the physiology of the retina. Often, ERGs are measured to flashes that are highly unnatural stimuli. To obtain more information about the physiology of the retina, we measured ERGs with temporal white noise (TWN) stimuli that are more natural and keep the retina in a normal range of operation. The stimuli can be combined with the silent substitution stimulation technique with which the responses of single photoreceptor types can be isolated. We characterized electroretinogram (ERG) responses driven by luminance activity or by the L- or the M-cones. The ERGs were measured from five anesthetized macaques (two females) to luminance, to L-cone isolating and to M-cone isolating stimuli in which luminance or cone excitation were modulated with a TWN profile. The responses from different recordings were correlated with each other to study reproducibility and inter-individual variability. Impulse response functions (IRFs) were derived by cross-correlating the response with the stimulus. Modulation transfer functions (MTFs) were the IRFs in the frequency domain. The responses to luminance and L-cone isolating stimuli showed the largest reproducibility. The M-cone driven responses showed the smallest inter-individual variability. The IRFs and MTFs showed early (high frequency) components that were dominated by L-cone driven signals. A late component was equally driven by L- and M-cone activity. The IRFs showed characteristic similarities and differences relative to flash ERGs. The responses to TWN stimuli can be used to characterize the involvement of retinal cells and pathways to the ERG response. It can also be used to identify linear and non-linear processes.

Use of an alternating current amplifier when recording the ERG c-wave to evaluate the function of retinal pigment epithelial cells in rats.

We studied the conditions under which c-waves of the electroretinogram (ERG), that represent retinal pigment epithelium (RPE) function, were detectable using an alternating current (AC) amplifier and whether the c-wave recorded using an AC amplifier was useful for evaluating RPE function. We recorded ERG responses in rats to 5s stimuli under the conditions in which the low-cut frequency and the stimulus luminance were varied. In addition, changes in ERGs were studied after intravenous injection of sodium iodate (SI) to induce RPE degeneration. The c-wave was detected clearly when the frequency of the low-cut filter was set at 0.01Hz and light stimulus luminances were ≥ - 1.0 log cd/m2. The c-wave was attenuated earlier than other waves (e.g., a-wave and b-wave) after SI administration. The c-wave was easily detectable using an AC amplifier with the low-cut filter set at 0.01Hz. Using the AC amplifier may allow easier c-wave recording, compared with the conventional use of a direct current (DC) amplifier, and could be useful for evaluating RPE function.

Inhibition of Heat Shock Protein B8 Alleviates Retinal Dysfunction and Ganglion Cells Loss Via Autophagy Suppression in Mouse Axonal Damage.

PurposeHeat shock protein B8 (HspB8) can be upregulated rapidly in many pathologic processes, but its role in traumatic optic neuropathy remains unclear. In this study, we investigated the involvement of autophagy in the effects of HspB8 by using the optic nerve crush (ONC) model.MethodsMale C57BL/6J mice were intravitreally injected with recombinant adeno-associated virus type 2 (AAV2-shHspB8 or AAV2-GFP) and subsequently received ONC by a self-closing tweezers. Western blot and immunohistochemistry staining were used to evaluate the expression of HspB8. We conducted retinal flat-mount immunofluorescence to measure the quantities of retinal ganglion cells (RGCs), and full-field flash electroretinogram (ff-ERG) and optomotor response (OMR) were used to evaluate retinal function. The autophagy level was reflected by western blot, immunohistochemistry staining, and transmission electron microscope (TEM) images. We also applied 3-methyladenine (3MA) and rapamycin (Rapa) to regulate autophagy level in optic nerve injury.ResultsONC stimulated the expression of HspB8. Declines of RGCs and ff-ERG b-wave amplitudes resulting from ONC can be alleviated by HspB8 downregulation. Increased autophagy activity after ONC was observed; however, this change can be reversed by intravitreal injection of AAV2-shHspB8. Furthermore, application of autophagy inhibitor 3MA had the same neuroprotective effects as AAV2-shHspB8, as illustrated by ff-ERG and quantities of RGCs. Also, protection of AAV2-shHspB8 was compromised by the autophagy activator Rapa.ConclusionsInhibition of HspB8 in mice optic nerve injury had neuroprotective effects, which may be derived from its downregulation of autophagy.

Supernormal rod response mediated by a novel KCNV2 variant in a cone dystrophy type 3B patient

The proband was an 8-year-old boy, complaining of progressively decreased vision in both eyes for 3 years. The electroretinogram was characterized by supernormal rod response. While the responses of the rod and cone system were reduced, the amplitudes of dark-adapted electroretinogram responses at a high intensity were supernormal. A homozygous non-frameshift deletion variant c.1002-1004del (p. L335del) in KCNV2 was found by the Next Generation Sequencing using a custom designed panel. His father was a heterozygous carrier of this variant. In silico analysis indicated the variant was harmful. The proband was diagnosed as cone dystrophy type 3B which also known as cone dystrophy with supernormal rod response.

Multifocal Electroretinogram Photopic Negative Response: A Reliable Paradigm to Detect Localized Retinal Ganglion Cells' Impairment in Retrobulbar Optic Neuritis Due to Multiple Sclerosis as a Model of Retinal Neurodegeneration.

The measure of the full-field photopic negative response (ff-PhNR) of light-adapted full-field electroretinogram (ff-ERG) allows to evaluate the function of the innermost retinal layers (IRL) containing primarily retinal ganglion cells (RGCs) and other non-neuronal elements of the entire retina. The aim of this study was to acquire functional information of localized IRL by measuring the PhNR in response to multifocal stimuli (mfPhNR). In this case-control observational and retrospective study, we assessed mfPhNR responses from 25 healthy controls and from 20 patients with multiple sclerosis with previous history of optic neuritis (MS-ON), with full recovery of visual acuity, IRL morphological impairment, and absence of morpho-functional involvement of outer retinal layers (ORL). MfPhNR response amplitude densities (RADs) were measured from concentric rings (R) with increasing foveal eccentricity: 0–5° (R1), 5–10° (R2), 10–15° (R3), 15–20° (R4), and 20–25° (R5) from retinal sectors (superior-temporal (ST), superior-nasal (SN), inferior-nasal (IN), and inferior-temporal (IT)); between 5° and 20° and from retinal sectors (superior (S), temporal (T), inferior (I), and nasal (N)); and within 5° to 10° and within 10° and 20° from the fovea. The mfPhNR RAD values observed in all rings or sectors in MS-ON eyes were significantly reduced (p < 0.01) with respect to control ones. Our results suggest that mfPhNR recordings may detect localized IRL dysfunction in the pathologic condition of selective RGCs neurodegeneration.