Intracellular responses of the Müller (glial) cells of mudpuppy retina: their relation to b-wave of the electroretinogram

The relationship between spectral signals and retinal sensitivity in dendrobatid frogs

Research on visually driven behavior in anurans has often focused on Dendrobatoidea, a clade with extensive variation in skin reflectance, which is perceived to range from cryptic to conspicuous coloration. Because these skin patterns are important in intraspecific and interspecific communication, we hypothesized that the visual spectral sensitivity of dendrobatids should vary with conspecific skin spectrum. We predicted that the physiological response of frog retinas would be tuned to portions of the visible light spectrum that match their body reflectance. Using wavelength-specific electroretinograms (ERGs; from 350-650 nm), spectrometer measurements, and color-calibrated photography of the skin, we compared retinal sensitivity and reflectance of two cryptic species (Allobates talamancae and Silverstoneia flotator), two intermediate species (Colostethus panamansis and Phyllobates lugubris), and two conspicuous aposematic species (Dendrobates tinctorius and Oophaga pumilio). Consistent with the matched filter hypothesis, the retinae of cryptic and intermediate species were sensitive across the spectrum, without evidence of spectral tuning to specific wavelengths, yielding low-threshold broadband sensitivity. In contrast, spectral tuning was found to be different between morphologically distinct populations of O. pumilio, where frogs exhibited retinal sensitivity better matching their morph's reflectance. This sensory specialization is particularly interesting given the rapid phenotypic divergence exhibited by this species and their behavioral preference for sympatric skin reflectances. Overall, this study suggests that retinal sensitivity is coevolving with reflective strategy and spectral reflectance in dendrobatids.

Slope between positive and negative ERG components in patients with open-angle glaucoma

PURPOSE

To evaluate ERG morphology, in particular the slope between P50 and N95 components of the PERG, as well as between the b-wave and the photopic negative response (PhNR) of the light-adapted (LA) ERG in patients with retinal ganglion cell (RGC) dysfunction due to open-angle glaucoma.

METHODS

The PERG and LA-ERG traces of 16 glaucoma patients and 21 age-similar controls were retrospectively analysed. The ERG signal between the peak of the positive component (P50 and b-wave) towards the negative component (N95 and PhNR) was described by a linear regression y = a + bx, where the parameter b indicated the steepness of the P50-N95 and b-PhNR slope.

RESULTS

The P50-N95 slope was less steep in glaucoma patients (-0.079 ± 0.034 vs. -0.166 ± 0.050 in controls, p < 0.001), while the b-PhNR slope was not affected (-4.2 ± 2.1 vs. -4.4 ± 1.2, p = NS). The P50-N95 slope showed strong correlation with PhNR and N95 amplitude (r = -0.68 and -0.92, respectively; p < 0.001), while the b-PhNR slope correlated only with b-wave amplitude (r = -0.66, p < 0.001).

CONCLUSIONS

The P50-N95 slope is a sensitive indicator of RGC dysfunction in patients with open-angle glaucoma. A similar component of LA-ERG, the b-PhNR slope, is less affected by glaucomatous RGC dysfunction and probably originates from similar retinal mechanisms as the b-wave.

S-cone contribution to oscillatory potentials in patients with blue cone monochromacy

PURPOSE

The aim of this exploratory study is to investigate the role of S-cones in oscillatory potentials (OPs) generation by individuals with blue-cone monochromacy (BCM), retaining S-cones, and achromatopsia (ACHM), lacking cone functions.

METHODS

This retrospective study analyzed data from 39 ACHM patients, 20 BCM patients, and 26 controls. Central foveal thickness was obtained using spectral-domain optical coherence tomography, while amplitude and implicit time (IT) of a- and b-waves were extracted from the ISCEV Standard dark-adapted 3 cd.s.m-2 full-field ERG (ffERG). Time-frequency analysis of the same measurement enabled the extraction of OPs, providing insights into the dynamic characteristics of the recorded signal.

RESULTS

Both ACHM and BCM groups showed a significant reduction (p < .00001) of a- and b-wave amplitudes and ITs as well as the power of the OPs compared to the control groups. The comparison between ACHM and BCM didn't show any statistically significant differences in the electrophysiological parameters. The analysis of covariance revealed significantly reduced central foveal thickness in the BCM group compared to ACHM and controls (p < .00001), and in ACHM compared to controls (p < .00001), after age correction and Tukey post-hoc analysis.

CONCLUSIONS

S-cones do not significantly influence OPs, and the decline in OPs' power is not solely due to a reduced a-wave. This suggests a complex non-linear network influenced by photoreceptor inputs. Morphological changes don't correlate directly with functional alterations, prompting further exploration of OPs' function and physiological role.

Nicotinamide mononucleotide, a potential future treatment in ocular diseases

PURPOSE

The burden of ocular diseases has been gradually increasing worldwide. Various factors are suggested for the development and progression of ocular diseases, such as ocular inflammation, oxidative stress, and complex metabolic dysregulation. Thus, managing ocular diseases requires the modulation of pathologic signaling pathways through many mechanisms. Nicotinamide mononucleotide (NMN) is a bioactive molecule naturally found in life forms. NMN is a direct precursor of the important molecule nicotinamide adenine dinucleotide (NAD+), an essential co-enzyme required for enormous cellular functions in most life forms. While the recent experimental evidence of NMN treatment in various metabolic diseases has been well-reviewed, NMN treatment in ocular diseases has not been comprehensively summarized yet. In this regard, we aimed to focus on the therapeutic roles of NMN treatment in various ocular diseases with recent advances.

METHODS

How we came to our current opinion with a recent summary was described based on our own recent reports as well as a search of the related literature.

RESULTS

We found that NMN treatment might be available for the prevention of and protection from various experimental ocular diseases, as NMN treatment modulated ocular inflammation, oxidative stress, and complex metabolic dysregulation in murine models for eye diseases such as ischemic retinopathy, corneal defect, glaucoma, and age-related macular degeneration.

CONCLUSION

Our current review suggests and discusses new modes of actions of NMN for the prevention of and protection from various ocular diseases and can urge future research to obtain more solid evidence on a potential future NMN treatment in ocular diseases at the preclinical stages.

The Role of Sphingosine-1-Phosphate Receptor 2 in Mouse Retina Light Responses

The bioactive sphingolipid sphingosine-1-phosphate (S1P) acts as a ligand for a family of G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways. However, their specific roles in the neural retina remain unclear. We previously showed that S1P receptor subtype 2 (S1PR2) is expressed in murine retinas, primarily in photoreceptors and bipolar cells, and its expression is altered by retinal stress. This study aims to elucidate the role of S1PR2 in the mouse retina. We examined light responses by electroretinography (ERG), structural differences by optical coherence tomography (OCT), and protein levels by immunohistochemistry (IHC) in wild-type (WT) and S1PR2 knockout (KO) mice at various ages between 3 and 6 months. We found that a- and b-wave responses significantly increased at flash intensities between 400~2000 and 4~2000 cd.s/m2, respectively, in S1PR2 KO mice relative to those of WT controls at baseline. S1PR2 KO mice also exhibited significantly increased retinal nerve fiber layer (RNFL) and outer plexiform layer (OPL) thickness by OCT relative to the WT. Finally, in S1PR2 KO mice, we observed differential labeling of synaptic markers by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (RT-qPCR). These results suggest a specific involvement of S1PR2 in the structure and synaptic organization of the retina and a potential role in light-mediated functioning of the retina.

The role of sphingosine-1-phosphate receptor 2 in mouse retina light responses

The bioactive sphingolipid sphingosine-1-phosphate (S1P) acts as a ligand for a family of G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways. However, their specific roles in the neural retina remain unclear. We previously showed that S1P receptor subtype 2 (S1PR2) is expressed in murine retinas, primarily in photoreceptors and bipolar cells, and its expression is altered by retinal stress. This study aims to elucidate the role of S1PR2 in the mouse retina. We examined light responses by electroretinography (ERG), structural differences by optical coherence tomography (OCT), and protein levels by immunohistochemistry (IHC) in wild-type (WT) and S1PR2 knockout (KO) mice at various ages between 3 and 6 months. We found that a- and b-wave responses significantly increased at flash intensities between 400∼2000 and 4∼2,000 cd.s/m 2 respectively, in S1PR2 KO mice relative to those of WT controls at baseline. S1PR2 KO mice also exhibited significantly increased retinal nerve fiber layer (RNFL) and outer plexiform layer (OPL) thickness by OCT relative to the WT. Finally, in S1PR2 KO mice, we observed differential labeling of synaptic markers by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (RT-qPCR). These results suggest a specific involvement of S1PR2 in the structure and synaptic organization of the retina and a potential role in light-mediated functioning of the retina.

The origins of the full-field flash electroretinogram b-wave

The electroretinogram (ERG) measures the electrical activity of retinal neurons and glial cells in response to a light stimulus. Amongst other techniques, clinicians utilize the ERG to diagnose various eye diseases, including inherited conditions such as cone-rod dystrophy, rod-cone dystrophy, retinitis pigmentosa and Usher syndrome, and to assess overall retinal health. An ERG measures the scotopic and photopic systems separately and mainly consists of an a-wave and a b-wave. The other major components of the dark-adapted ERG response include the oscillatory potentials, c-wave, and d-wave. The dark-adapted a-wave is the initial corneal negative wave that arises from the outer segments of the rod and cone photoreceptors hyperpolarizing in response to a light stimulus. This is followed by the slower, positive, and prolonged b-wave, whose origins remain elusive. Despite a large body of work, there remains controversy around the mechanisms involved in the generation of the b-wave. Several hypotheses attribute the origins of the b-wave to bipolar or Müller glial cells or a dual contribution from both cell types. This review will discuss the current hypothesis for the cellular origins of the dark-adapted ERG, with a focus on the b-wave.

Development of a rabbit model of Adenosine triphosphate-induced monocular retinal degeneration for optimization of retinal prostheses

Optimization of retinal prostheses requires preclinical animal models that mimic features of human retinal disease, have appropriate eye sizes to accommodate implantable arrays, and provide options for unilateral degeneration so as to enable a contralateral, within-animal control eye. In absence of a suitable non-human primate model and shortcomings of our previous feline model generated through intravitreal injections of Adenosine Triphosphate (ATP), we aimed in the present study to develop an ATP induced degeneration model in the rabbit. Six normally sighted Dutch rabbits were monocularly blinded with this technique. Subsequent retinal degeneration was assessed with optical coherence tomography, electroretinography, and histological assays. Overall, there was a 42% and 26% reduction in a-wave and oscillatory potential amplitudes in the electroretinograms respectively, along with a global decrease in retinal thickness, with increased variability. Qualitative inspection also revealed that there were variable levels of retinal degeneration and remodeling both within and between treated eyes, mimicking the disease heterogeneity observed in retinitis pigmentosa. These findings confirm that ATP can be utilized to unilaterally induce blinding in rabbits and, potentially present an ideal model for future cortical recording experiments aimed at optimizing vision restoration strategies.Clinical Relevance- A rapid, unilaterally induced model of retinal degeneration in an animal with low binocular overlap and large eyes will allow for clinically valid recordings of downstream cortical activity following retinal stimulation. Such a model would be highly beneficial for the optimization of clinically appropriate vision restoration approaches.

Ribbon Synapses and Retinal Disease: Review

Synaptic ribbons are presynaptic protein complexes that are believed to be important for the transmission of sensory information in the visual system. Ribbons are selectively associated with those synapses where graded changes in membrane potential drive continuous neurotransmitter release. Defective synaptic transmission can arise as a result of the mutagenesis of a single ribbon component. Visual diseases that stem from malfunctions in the presynaptic molecular machinery of ribbon synapses in the retina are rare. In this review, we provide an overview of synaptopathies that give rise to retinal malfunction and our present understanding of the mechanisms that underlie their pathogenesis and discuss muscular dystrophies that exhibit ribbon synapse involvement in the pathology.

Impact of keratoprosthesis implantation on retinal and visual pathway function assessed by electrophysiological testing

PURPOSE

To investigate the impact of Boston Type I Keratoprosthesis (BI-Kpro) implantation on retinal and visual pathway function, respectively, assessed by full-field electroretinography (ERG) and visually evoked potentials (VEPs).

METHODS

This is a prospective interventional longitudinal study, and patients with BI-Kpro implantation were assessed preoperatively and at 3 and 12 months after surgery. ERG, flash, and pattern-reversal VEPs (15' and 60' checks) along with visual acuity (VA) were performed.

RESULTS

A total of 13 patients (24 to 88 years of age) were included. Mean baseline VA (logMAR) improved from 2.30 to 1.04 at 3 months and to 1.00 at 12 months. Flash VEPs were normal in 6 (46%) patients and in 10 (77%) patients at the 12-month follow-up. PVEP was non-detectable in all patients preoperatively for both check sizes. For 15' check size, 6 (46%) patients showed responses after 3 and 12 months except for 1 patient with normal responses at 12 months with the remaining non-detectable. For 60' checks, 11 (85%) patients had responses 3 months after surgery with only 9 (70%) showing responses at 12 months. Abnormal full-field ERGs were found in all patients preoperatively. Amplitude improvement was found in 10 (77%) patients from baseline to 3 months and in 8 (62%) patients from the 3- to the 12-month follow-up.

CONCLUSIONS

In this small cohort of patients with BI-Kpro implantation, a remarkable improvement on visual function quantitatively assessed by electrophysiological testing was found in the majority of cases. Visual electrophysiological testing can contribute to objectively assess functional outcomes in this population.

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.

Differences in junction-associated gene expression changes in three rat models of diabetic retinopathy with similar neurovascular phenotype

Diabetic retinopathy, also defined as microvascular complication of diabetes mellitus, affects the entire neurovascular unit with specific aberrations in every compartment. Neurodegeneration, glial activation and vasoregression are observed consistently in models of diabetic retinopathy. However, the order and the severity of these aberrations varies in different models, which is also true in patients. In this study, we analysed rat models of diabetic retinopathy with similar phenotypes to identify key differences in the pathogenesis. For this, we focussed on intercellular junction-associated gene expression, which are important for the communication and homeostasis within the neurovascular unit. Streptozotocin-injected diabetic Wistar rats, methylglyoxal supplemented Wistar rats and polycystin-2 transgenic (PKD) rats were analysed for neuroretinal function, vasoregression and retinal expression of junction-associated proteins. In all three models, neuroretinal impairment and vasoregression were observed, but gene expression profiling of junction-associated proteins demonstrated nearly no overlap between the three models. However, the differently expressed genes were from the main classes of claudins, connexins and integrins in all models. Changes in Rcor1 expression in diabetic rats and Egr1 expression in PKD rats confirmed the differences in upstream transcription factor level between the models. In PKD rats, a possible role for miRNA regulation was observed, indicated by an upregulation of miR-26b-5p, miR-122-5p and miR-300-3p, which was not observed in the other models. In silico allocation of connexins revealed not only differences in regulated subtypes, but also in affected retinal cell types, as well as connexin specific upstream regulators Sox7 and miR-92a-3p. In this study, we demonstrate that, despite their similar phenotype, models for diabetic retinopathy exhibit significant differences in their pathogenic pathways and primarily affected cell types. These results underline the importance for more sensitive diagnostic tools to identify pathogenic clusters in patients as the next step towards a desperately needed personalized therapy.

Review: Use of Electrophysiological Techniques to Study Visual Functions of Aquatic Organisms

The light environments of natural water sources have specific characteristics. For the majority of aquatic organisms, vision is crucial for predation, hiding from predators, communicating information, and reproduction. Electroretinography (ERG) is a diagnostic method used for assessing visual function. An electroretinogram records the comprehensive potential response of retinal cells under light stimuli and divides it into several components. Unique wave components are derived from different retinal cells, thus retinal function can be determined by analyzing these components. This review provides an overview of the milestones of ERG technology, describing how ERG is used to study visual sensitivity (e.g., spectral sensitivity, luminous sensitivity, and temporal resolution) of fish, crustaceans, mollusks, and other aquatic organisms (seals, sea lions, sea turtles, horseshoe crabs, and jellyfish). In addition, it describes the correlations between visual sensitivity and habitat, the variation of visual sensitivity as a function of individual growth, and the diel cycle changes of visual sensitivity. Efforts to identify the visual sensitivity of different aquatic organisms are vital to understanding the environmental plasticity of biological evolution and for directing aquaculture, marine fishery, and ecosystem management.

Glucosamine protects against neuronal but not vascular damage in experimental diabetic retinopathy

Objective

Glucosamine, an intermetabolite of the hexosamine biosynthesis pathway (HBP), is a widely used nutritional supplement in osteoarthritis patients, a subset of whom also suffer from diabetes. HBP is activated in diabetic retinopathy (DR). The aim of this study is to investigate the yet unclear effects of glucosamine on DR.

Methods

In this study, we tested the effect of glucosamine on vascular and neuronal pathology in a mouse model of streptozotocin-induced DR in vivo and on cultured endothelial and Müller cells to elucidate the underlying mechanisms of action in vitro.

Results

Glucosamine did not alter the blood glucose or HbA_1c levels in the animals, but induced body weight gain in the non-diabetic animals. Interestingly, the impaired neuronal function in diabetic animals could be prevented by glucosamine treatment. Correspondingly, the activation of Müller cells was prevented in the retina as well as in cell culture. Conversely, glucosamine administration in the normal retina damaged the retinal vasculature by increasing pericyte loss and acellular capillary formation, likely by interfering with endothelial survival signals as seen in vitro in cultured endothelial cells. Nevertheless, under diabetic conditions, no further increase in the detrimental effects were observed.

Conclusions

In conclusion, the effects of glucosamine supplementation in the retina appear to be a double-edged sword: neuronal protection in the diabetic retina and vascular damage in the normal retina. Thus, glucosamine supplementation in osteoarthritis patients with or without diabetes should be taken with care.

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The hexosamine biosynthesis pathway (HBP) is activated in diabetic retinopathy (DR), which manifests as vascular and neuronal damage in the retina.

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Glucosamine, metabolized in the HBP, is a widely used oral supplement for osteoarthritis treatment.

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Glucosamine supplementation improved neuronal function in retinas of mice with experimental DR, but induced vascular damage in normal retinas.

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Müller cell activation and endothelial survival signals in the retina were affected by glucosamine.

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Patients with or without diabetes should take caution with glucosamine supplementation.

Sex-Specific Retinal Anomalies Induced by Chronic Social Defeat Stress in Mice

Major depressive disorder (MDD) is one of the most common consequences of chronic stress. Still, there is currently no reliable biomarker to detect individuals at risk to develop the disease. Recently, the retina emerged as an effective way to investigate psychiatric disorders using the electroretinogram (ERG). In this study, cone and rod ERGs were performed in male and female C57BL/6 mice before and after chronic social defeat stress (CSDS). Mice were then divided as susceptible or resilient to stress. Our results suggest that CSDS reduces the amplitude of both oscillatory potentials and a-waves in the rods of resilient but not susceptible males. Similar effects were revealed following the analysis of the cone b-waves, which were faster after CSDS in resilient mice specifically. In females, rod ERGs revealed age-related changes with no change in cone ERGs. Finally, our analysis suggests that baseline ERG can predict with an efficacy up to 71% the expression of susceptibility and resilience before stress exposition in males and females. Overall, our findings suggest that retinal activity is a valid biomarker of stress response that could potentially serve as a tool to predict whether males and females will become susceptible or resilient when facing CSDS.

Ocular safety of repeated intravitreal injections of Carboplatin and Digoxin: A preclinical study on the healthy rabbits

To evaluate the ocular safety of intravitreal carboplatin and digoxin injections as a new intravitreal chemotherapy option for retinoblastoma tumor vitreous seeds. Eighteen rabbits were divided randomly into three groups to receive intravitreal injection of Digoxin (6 rabbits), Carboplatin (7 rabbits), or Saline (5 rabbits). In every group, one eye randomly treated with 10 µg Digoxin in 0.1 cc or 1 µg Carboplatin or Saline, and the contralateral eye was considered as the control. All groups underwent three consecutive injections of the drugs with 1-week intervals. Baseline electroretinography (ERG) was recorded from both eyes of all the animals prior to injection and was repeated 1st day, 1st week, and 1st month after the last injection. All rabbits were sacrificed 1 month after the last injection, and histological studies were done. Mean a and b wave amplitudes decreased significantly at 1st day, 1st week, and 1st month after the last intravitreal injection of 10 µg Digoxin in comparison with other groups (p-value: .02). Contradictory, 1 µg Carboplatin injected eyes had minimal ERG changes. There were some nonspecific ERG changes with unclear clinical significance in non-injected contralateral control eyes of Digoxin and Carboplatin groups in comparison with the control eyes of the Saline group. Histological studies revealed considerable neural retinal atrophy in injected eyes of the Digoxin group. Intravitreal 10 µg Digoxin might have more local ocular toxicity in comparison with intravitreal Carboplatin in albino rabbit eyes. Future studies should assess the induced toxicity of intravitreal injection of these drugs on the non-injected contralateral eye.

Expanding the phenotype of mucopolysaccharidosis type II retinopathy

Purpose: To report novel retinal findings in two male patients with mucopolysaccharidosis type II (Hunter syndrome) receiving long-term human recombinant idursulfase enzyme replacement therapy.Method: Two males aged 19 and 26 years who had received enzyme replacement therapy for 12 and 13 years, respectively, with good compliance and no infusion-related reactions, were examined clinically and underwent optical coherence tomographic scanning of the retina and electroretinography testing.Results: Case 1 had visual acuity 20/32 in each eye and case 2 had visual acuity 20/25 in each eye. Both patients had clinically unremarkable anterior segment and fundus examinations. Ocular coherence tomography imaging in both patients showed thickening of the external limiting membrane with hyperreflective material in at least one eye each. One patient had bilateral foveoschisis and the other had mild foveal hypoplasia. Electroretinography showed a negative response in the patient with foveoschisis and reduced amplitudes in the patient with foveal hypoplasia.Conclusions: These two patients with Hunter syndrome receiving idursulfase treatment both have subfoveal deposition of hyperreflective material in the external limiting membrane despite good compliance and tolerance of the standard dose of enzyme therapy for this disorder. One patient has developed foveoschisis and negative electroretinogram suggesting abnormality of inner retinal function. Further studies are needed to determine the nature of the hyperreflective material, as well as the effect of systemic treatment on retinal findings in patients with mucopolysaccharidosis type II.

Retinal dysfunction induced in a mouse model of unilateral common carotid artery occlusion

Background

Retinal ischemic stresses are associated with the pathogenesis of various retinal vascular diseases. To investigate pathological mechanisms of retinal ischemia, reproducible, robust and clinically significant experimental rodent models are highly needed. Previously, we established a stable murine model of chronic hypoperfusion retinal injuries by permanent unilateral common carotid artery occlusion (UCCAO) and demonstrated chronic pathological processes in the ischemic retina after the occlusion; however, retinal functional deficits and other acute retinal ischemic injuries by UCCAO still remain obscure. In this study, we attempted to examine retinal functional changes as well as acute retinal ischemic alterations such as retinal thinning, gliosis and cell death after UCCAO.

Methods

Adult mice (male C57BL/6, 6–8 weeks old) were subjected to UCCAO in the right side, and retinal function was primarily measured using electroretinography for 14 days after the surgery. Furthermore, retinal thinning, gliosis and cell death were investigated using optical coherence tomography, immunohistochemistry and TUNEL assay, respectively.

Results

Functional deficits in the unilateral right retina started to be seen 7 days after the occlusion. Specifically, the amplitude of b-wave dramatically decreased while that of a-wave was slightly affected. 14 days after the occlusion, the amplitudes of both waves and oscillatory potentials were significantly detected decreased in the unilateral right retina. Even though a change in retinal thickness was not dramatically observed among all the eyes, retinal gliosis and cell death in the unilateral right retina were substantially observed after UCCAO.

Conclusions

Along with previous retinal ischemic results in this model, UCCAO can stimulate retinal ischemia leading to functional, morphological and molecular changes in the retina. This model can be useful for the investigation of pathological mechanisms for human ischemic retinopathies and furthermore can be utilized to test new drugs for various ischemic ocular diseases.

Estrogenic Modulation of Retinal Sensitivity in Reproductive Female Túngara Frogs

Although mate searching behavior in female túngara frogs (Physalaemus pustulosus) is nocturnal and largely mediated by acoustic cues, male signaling includes visual cues produced by the vocal sac. To compensate for these low light conditions, visual sensitivity in females is modulated when they are in a reproductive state, as retinal thresholds are decreased. This study tested whether estradiol (E2) plays a role in this modulation. Female túngara frogs were injected with either human chorionic gonadotropin (hCG) or a combination of hCG and fadrozole. hCG induces a reproductive state and increases retinal sensitivity, while fadrozole is an aromatase inhibitor that blocks hCG-induced E2 synthesis. In an analysis of scotopic electroretinograms (ERGs), hCG treatment lowered the threshold for eliciting a b-wave response, whereas the addition of fadrozole abolished this effect, matching thresholds in non-reproductive saline-injected controls. This suggests that blocking E2 synthesis blocked the hCG-mediated reproductive modulation of retinal sensitivity. By implicating E2 in control of retinal sensitivity, our data add to growing evidence that the targets of gonadal steroid feedback loops include sensory receptor organs, where stimulus sensitivity may be modulated, rather than more central brain nuclei, where modulation may affect mechanisms involved in motivation.

Fenofibrate Protects against Retinal Dysfunction in a Murine Model of Common Carotid Artery Occlusion-Induced Ocular Ischemia

Ocular ischemia is a common cause of blindness and plays a detrimental role in various diseases such as diabetic retinopathy, occlusion of central retinal arteries, and ocular ischemic syndrome. Abnormalities of neuronal activities in the eye occur under ocular ischemic conditions. Therefore, protecting their activities may prevent vision loss. Previously, peroxisome proliferator-activated receptor alpha (PPARα) agonists were suggested as promising drugs in ocular ischemia. However, the potential therapeutic roles of PPARα agonists in ocular ischemia are still unknown. Thus, we attempted to unravel systemic and ocular changes by treatment of fenofibrate, a well-known PPARα agonist, in a new murine model of ocular ischemia. Adult mice were orally administered fenofibrate (60 mg/kg) for 4 days once a day, followed by induction of ocular ischemia by unilateral common carotid artery occlusion (UCCAO). After UCCAO, fenofibrate was continuously supplied to mice once every 2 days during the experiment period. Electroretinography was performed to measure retinal functional changes. Furthermore, samples from the retina, liver, and blood were subjected to qPCR, Western blot, or ELISA analysis. We found that fenofibrate boosted liver function, increased serum levels of fibroblast growth factor 21 (FGF21), one of the neuroprotective molecules in the central nervous system, and protected against UCCAO-induced retinal dysfunction. Our current data suggest a promising fenofibrate therapy in ischemic retinopathies.

Child with a mild phenotype of Incontinentia Pigmenti and inner retinal dysfunction

PURPOSE

To describe a case of a child with mild phenotype of Incontinentia Pigmenti (IP), with changes in Spectral-Domain Optical Coherence Tomography (SD-OCT) and Optical Coherence Tomography Angiography (OCT-A) and an electronegative dark-adapted (DA) 3.0 electroretinogram (ERG), suggestive of inner retinal dysfunction.

CASE REPORT

We described a 7-year-old female child with IP. Her best corrected acuity was 8/10 in the right eye and 6/10 in the left eye. Biomicroscopy, intraocular pressure and fundoscopy were normal. The electroretinography findings showed an electronegative DA 3.0 ERG with a normal a-wave but a b-wave that did not elevate above baseline. SD-OCT identified irregularities in the outer plexiform layer in both eyes, and OCT-A assessment revealed at the superficial capillary plexus, areas of decrease in the flow in parafoveal and perifoveal regions.

CONCLUSION

Classically, IP affects the peripheral retina; however, vascular and structural changes in macula can occur as well. To our knowledge, we report the first electronegative electroretinogram in a patient with IP.

Autosomal recessive Stickler syndrome associated with homozygous mutations in the COL9A2 gene

Background: Stickler syndrome is a hereditary disorder of collagen tissues causing ocular, auditory, orofacial, and joint manifestations. Ocular findings typically include vitreous degeneration, high myopia, retinal detachment, and cataract. Many subjects demonstrate sensorineural or conductive hearing loss. The inheritance is autosomal dominant with mutations in COL2A1, COL11A1, or COL11A2 or autosomal recessive due to mutations in COL9A1, COL9A2, or COL9A3. We describe a family with Stickler syndrome caused by homozygous loss-of-function mutations in COL9A2.Methods: Two brothers from a consanguineous family were examined with genetic testing, visual acuity, Goldmann perimetry, full-field and multifocal electroretinography (ffERG, mERG), optical coherence tomography (OCT), fundus autofluorescence (FAF), fundus photography, and pure-tone audiograms.Results: Both subjects were homozygous for the mutation c.1332del in COL9A2. Their parents were heterozygous for the same mutation. The boys demonstrated reduced visual acuity, vitreous changes and myopia. The proband was operated for retinal detachment and cataract in one eye. FfERG revealed reduced function of both rods and cones and mERG showed reduced macular function. No morphological macular changes were found by OCT or FAF. Both brothers have severe sensorineural hearing loss with down-sloping audiograms but only subtle midface hypoplasia and no, or mild joint problems.Conclusion: Only a few families with Stickler syndrome caused by COL9A2 mutations have been reported. We confirm previous descriptions with a severe ocular and auditory phenotype but mild orofacial and joint manifestations. Moreover, we demonstrate reduced macular and overall retinal function explaining the reduced visual acuity in patients with Stickler syndrome also without retinal complications.

The photopic negative response (PhNR): measurement approaches and utility in glaucoma

Purpose

Visual electrophysiological testing continues to generate interest among glaucoma experts because of its potential help in clarifying disease pathophysiology and promoting early detection of glaucomatous damage. The photopic negative response (PhNR) is a slow negative component of the full-field electroretinogram that has been shown to provide specific information about retinal ganglion cells (RGCs) activity. The purpose of this article is to review the literature to explore the currently available measurement methods and the utility of PhNR in glaucoma diagnostic process.

Methods

We gathered publications related to the origins, types of stimuli used, measurements methods and applications of the PhNR of ERG in animal models and humans through a search of the literature cited in PubMed. Search terms were: “PhNR”, “photopic negative response”, “glaucoma”, “glaucomatous optic neuropathy”, “ERG”, “electroretinogram”.

Results

The most reliable PhNR measurements are obtained using a red stimulus on a blue background, without requiring refractive correction, fixation monitoring, or ocular media transparency. Given its direct correlation with RGCs response, the PhNR measured as baseline-to-trough (BT) represents the most reliable parameter of evaluation. Glaucoma patients with evident perimetric defects show pathologic PhNR values. Even though the PhNR is promising in detecting early RGCs impairment, distinguishing between healthy subjects and suspect patients at risk of developing glaucomatous damage still remains challenging.

Conclusion

The PhNR is a useful additional tool to explore disorders that affect the innermost retina, including glaucoma and other forms of optic neuropathy. In particular, comparing reports of the standard examinations (optic disc assessment, OCT RNFL measurement, standard automated perimetry) with the results of electrophysiological tests may be helpful in solving clinical diagnostic and management dilemmas. On the one hand, the PhNR of the ERG can examine the parvocellular pathways; on the other hand, the steady-state pattern ERG optimized for glaucoma screening (PERGLA) can explore the magnocellular pathways. This could give ophthalmologists a useful feedback to identify early RGCs alterations suggestive of glaucoma, stratify the risk and potentially monitor disease progression.

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.

Retinal functioning and reward processing in schizophrenia

Retinal responses to light, as measured by electroretinography (ERG), have been shown to be reduced in schizophrenia. Data from a prior ERG study in healthy humans indicated that activity of a retinal cell type affected in schizophrenia can be modified by the presence of a food reward. Therefore, we aimed to determine whether ERG amplitudes would be sensitive to the well-documented reward processing impairment in schizophrenia. Flash ERG data from 15 clinically stable people with schizophrenia or schizoaffective disorder and 15 healthy controls were collected under three conditions: baseline, anticipation of a food reward, and immediately after consuming the food reward. At the group level, data indicated that controls' ERG responses varied as a function of salience of the food reward (baseline vs. anticipation vs. consumption) whereas patients' ERG responses did not vary significantly across conditions. Correlations between ERG amplitudes and scores on measures of hedonic capacity (including motivation and pleasure negative symptom ratings for patients) indicated consistent relationships. These data suggest that flash ERG amplitudes may be a sensitive indicator of the integrity of reward processing mechanisms. However, several differences in the direction of findings between this and a prior study in controls point to the need for further investigation of the contributions of a number of key variables to the observed effects.

Rescue of Defective Electroretinographic Responses in Dp71-Null Mice With AAV-Mediated Reexpression of Dp71

Purpose

To study the potential effect of a gene therapy, designed to rescue the expression of dystrophin Dp71 in the retinas of Dp71-null mice, on retinal physiology.

Methods

We recorded electroretinograms (ERGs) in Dp71-null and wild-type littermate mice. In dark-adapted eyes, responses to flashes of several strengths were measured. In addition, flash responses on a 25-candela/square meters background were measured. On- and Off-mediated responses to sawtooth stimuli and responses to photopic sine-wave modulation (3–30 Hz) were also recorded. After establishing the ERG phenotype, the ShH10-GFP adeno-associated virus (AAV), which has been previously shown to target specifically Müller glial cells (MGCs), was delivered intravitreously with or without (sham therapy) the Dp71 coding sequence under control of a CBA promoter. ERG recordings were repeated three months after treatment. Real-time quantitative PCR and Western blotting analyses were performed in order to quantify Dp71 expression in the retinas.

Results

Dp71-null mice displayed reduced b-waves in dark- and light-adapted flash ERGs and smaller response amplitudes to photopic rapid-on sawtooth modulation and to sine-wave stimuli. Three months after intravitreal injections of the ShH10-GFP-2A-Dp71 AAV vector, ERG responses were completely recovered in treated eyes of Dp71-null mice. The functional rescue was associated with an overexpression of Dp71 in treated retinas.

Conclusions

The present results show successful functional recovery accompanying the reexpression of Dp71. In addition, this experimental model sheds light on MGCs influencing ERG components, since previous reports showed that aquaporin 4 and Kir4.1 channels were mislocated in MGCs of Dp71-null mice, while their distribution could be normalized following intravitreal delivery of the same ShH10-GFP-2A-Dp71 vector.

A review of electroretinography waveforms and models and their application in the dog

Electroretinography (ERG) is a commonly used technique to study retinal function in both clinical and research ophthalmology. ERG responses can be divided into component waveforms, analysis of which can provide insight into the health and function of different types and populations of retinal cells. In dogs, ERG has been used in the characterization of normal retinal function, as well as the diagnosis of retinal diseases and measuring effects of treatment. While many components of the recorded waveform are similar across species, dogs have several notable features that should be differentiated from the responses in humans and other animals. Additionally, modifications of standard protocols, such as changing flash frequency and stimulus color, and mathematical models of ERG waveforms have been used in studies of human retinal function but have been infrequently applied to visual electrophysiology in dogs. This review provides an overview of the origins and applications of ERG in addition to potential avenues for further characterization of responses in the dog.

Reproductive State Modulates Retinal Sensitivity to Light in Female Túngara Frogs

Visual cues are often a vital part of animal communication and courtship. While a plethora of studies have focused on the role that hormones play in acoustic communication of anurans, relatively few have explored hormonal modulation of vision in these animals. Much of what we do know comes from behavioral studies, which show that a frog’s hormonal state can significantly affect both its visual behavior and mating decisions. However, to fully understand how frogs use visual cues to make these mating decisions, we must first understand how their visual system processes these cues, and how hormones affect these processes. To do this, we performed electroretinograms (ERGs) to measure retinal sensitivity of túngara frogs (Physalaemus pustulosus), a neotropical species whose mating behavior includes previously described visual cues. To determine the effect of hormonal state on visual sensitivity, ERGs were recorded under scotopic and photopic conditions in frogs that were either non-reproductive or hormone-treated with human chorionic gonadotropin (hCG) prior to testing. Additionally, measurements of optical anatomy determined how túngara frog eye and retina morphology related to physiological sensitivity. As expected, we found that both sexes display higher visual sensitivity under scotopic conditions compared to photopic conditions. However, hormone injections significantly increased retinal sensitivity of females under scotopic conditions. These results support the hypothesis that hormonal modulation of neural mechanisms, such as those mediating visually guided reproductive behavior in this species, include modulation of the receptor organ: the retina. Thus, our data serve as a starting point for elucidating the mechanism of hormonal modulation of visual sensitivity.

Retinal correlates of neurological disorders

Considering the retina as an extension of the brain provides a platform from which to study diseases of the nervous system. Taking advantage of the clear optical media of the eye and ever-increasing resolution of modern imaging techniques, retinal morphology can now be visualized at a cellular level in vivo. This has provided a multitude of possible biomarkers and investigative surrogates that may be used to identify, monitor and study diseases until now limited to the brain. In many neurodegenerative conditions, early diagnosis is often very challenging due to the lack of tests with high sensitivity and specificity, but, once made, opens the door to patients accessing the correct treatment that can potentially improve functional outcomes. Using retinal biomarkers in vivo as an additional diagnostic tool may help overcome the need for invasive tests and histological specimens, and offers the opportunity to longitudinally monitor individuals over time. This review aims to summarise retinal biomarkers associated with a range of neurological conditions including Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) and prion diseases from a clinical perspective. By comparing their similarities and differences according to primary pathological processes, we hope to show how retinal correlates can aid clinical decisions, and accelerate the study of this rapidly developing area of research.

Müller Cell-Localized G-Protein-Coupled Receptor 81 (Hydroxycarboxylic Acid Receptor 1) Regulates Inner Retinal Vasculature via Norrin/Wnt Pathways

Ischemic retinopathies are characterized by a progressive microvascular degeneration followed by a postischemic aberrant neovascularization. To reinstate vascular supply and metabolic equilibrium to the ischemic tissue during ischemic retinopathies, a dysregulated production of growth factors and metabolic intermediates occurs, promoting retinal angiogenesis. Glycolysis-derived lactate, highly produced during ischemic conditions, has been associated with tumor angiogenesis and wound healing. Lactate exerts its biological effects via G-protein-coupled receptor 81 (GPR81) in several tissues; however, its physiological functions and mechanisms of action in the retina remain poorly understood. Herein, we show that GPR81, localized predominantly in Müller cells, governs deep vascular complex formation during development and in ischemic retinopathy. Lactate-stimulated GPR81 Müller cells produce numerous angiogenic factors, including Wnt ligands and particularly Norrin, which contributes significantly in triggering inner retinal blood vessel formation. Conversely, GPR81-null mice retina shows reduced inner vascular network formation associated with low levels of Norrin (and Wnt ligands). Lactate accumulation during ischemic retinopathy selectively activates GPR81-extracellular signal-regulated kinase 1/2-Norrin signaling to accelerate inner retinal vascularization in wild-type animals, but not in the retina of GPR81-null mice. Altogether, we reveal that lactate via GPR81-Norrin participates in inner vascular network development and in restoration of the vasculature in response to injury. These findings suggest a new potential therapeutic target to alleviate ischemic diseases.

Cinnamon Attenuated Long-Term IGT-Induced Retinal Abnormalities via Regulation of Glucose Homeostasis in Neonatal Streptozotocin Induced Rat Model

Diabetic retinopathy (DR) is one of the major causes of blindness all over the world. According to the previous studies, impaired glucose tolerance (IGT) has been linked to retinal dysfunction/vascular damage. Decreased retinal function is an initial event of early DR. Although the biochemical and molecular events are not fully understood, glial activation, angiogenesis and oxidative stress are some of the pathways associated with early retinal abnormalities. Since IGT is associated with development of retinal dysfunction/vascular damage; as a preventive strategy, we have studied beneficial effect of Cinnamon as a hypoglycaemic agent on long-term IGT induced retinal abnormalities using neonatal streptozotocin (nSTZ) rat model. Control, IGT rats were maintained on AIN-93M diet alone and another set of IGT rats were maintained on AIN-93M diet with 3% Cinnamon for 8 months. At the end of the study, untreated IGT rats developed retinal functional abnormalities as assessed by electroretinogram (ERG) and the retinal structure did not alter as assessed by H&E staining. Further, increase in expressions of GFAP, VEGF and decreased expression of rhodopsin in untreated IGT rat retinas. 4-HNE, a marker of oxidative stress was also elevated in IGT state. Supplementation of Cinnamon to IGT rats had lowered fasting and postprandial glucose levels and also prevented retinal functional abnormalities. Further, Cinnamon protected photoreceptor cell damage, suppressed glial activation, angiogenesis and oxidative stress as there was an improved rhodopsin expression, inhibited elevated expressions of GFAP, VEGF and 4-HNE respectively. In conclusion, Cinnamon attenuated IGT induced retinal abnormalities probably through its hypoglycemic property.

A longitudinal study of retinopathy in the PEX1-Gly844Asp mouse model for mild Zellweger Spectrum Disorder

Zellweger Spectrum Disorder (ZSD) is an autosomal recessive disease caused by mutations in any one of 13 PEX genes whose protein products are required for peroxisome assembly. Retinopathy leading to blindness is one of the major untreatable handicaps faced by patients with ZSD but is not well characterized, and the requirement for peroxisomes in retinal health is unknown. To address this, we examined the progression of retinopathy from 2 to 32 weeks of age in our murine model for the common human PEX1-p.Gly843Asp allele (PEX1-p.Gly844Asp) using electrophysiology, histology, immunohistochemistry, electron microscopy, biochemistry, and visual function tests. We found that retinopathy in male and female PEX1-G844D mice was marked by an attenuated cone function and abnormal cone morphology early in life, with gradually decreasing rod function. Structural defects at the inner retina occurred later in the form of bipolar cell degradation (between 13 and 32 weeks). Inner segment disorganization and enlarged mitochondria were seen at 32 weeks, while other inner retinal cells appeared preserved. Visual acuity was diminished by 11 weeks of age, while signal transmission from the retina to the brain was relatively intact from 7 to 32 weeks of age. Molecular analyses showed that PEX1-G844D is a subfunctional but stable protein, contrary to human PEX1-G843D. Finally, C26:0 lysophosphatidylcholine was elevated in the PEX1-G844D retina, while phopshoethanolamine plasmalogen lipids were present at normal levels. These characterization studies identify therapeutic endpoints for future preclinical trials, including improving or preserving the electroretinogram response, improving visual acuity, and/or preventing loss of bipolar cells.

A Life in Vision

I was drawn into research in George Wald's laboratory at Harvard, where as an undergraduate and graduate student, I studied vitamin A deficiency and dark adaptation. A chance observation while an assistant professor at Harvard led to the major research of my career-to understand the functional organization of vertebrate retinas. I started with a retinal circuit analysis of the primate retina with Brian Boycott and intracellular retinal cell recordings in mudpuppies with Frank Werblin. Subsequent pharmacology studies with Berndt Ehinger primarily with fish focused on dopamine and neuromodulation. Using zebrafish, we studied retinal development, neuronal connectivity, and the effects of genetic mutations on retinal structure and function. Now semi-retired, I have returned to primate retinal circuitry, undertaking a connectomic analysis of the human fovea in Jeffrey Lichtman's laboratory.

The Role of the Voltage-Gated Potassium Channel Proteins Kv8.2 and Kv2.1 in Vision and Retinal Disease: Insights from the Study of Mouse Gene Knock-Out Mutations

Mutations in the KCNV2 gene, which encodes the voltage-gated K⁺ channel protein Kv8.2, cause a distinctive form of cone dystrophy with a supernormal rod response (CDSRR). Kv8.2 channel subunits only form functional channels when combined in a heterotetramer with Kv2.1 subunits encoded by the KCNB1 gene. The CDSRR disease phenotype indicates that photoreceptor adaptation is disrupted. The electroretinogram (ERG) response of affected individuals shows depressed rod and cone activity, but what distinguishes this disease is the supernormal rod response to a bright flash of light. Here, we have utilized knock-out mutations of both genes in the mouse to study the pathophysiology of CDSRR. The Kv8.2 knock-out (KO) mice show many similarities to the human disorder, including a depressed a-wave and an elevated b-wave response with bright light stimulation. Optical coherence tomography (OCT) imaging and immunohistochemistry indicate that the changes in six-month-old Kv8.2 KO retinae are largely limited to the outer nuclear layer (ONL), while outer segments appear intact. In addition, there is a significant increase in TUNEL-positive cells throughout the retina. The Kv2.1 KO and double KO mice also show a severely depressed a-wave, but the elevated b-wave response is absent. Interestingly, in all three KO genotypes, the c-wave is totally absent. The differential response shown here of these KO lines, that either possess homomeric channels or lack channels completely, has provided further insights into the role of K⁺ channels in the generation of the a-, b-, and c-wave components of the ERG.

Quantifying the relationship between optical anatomy and retinal physiological sensitivity: A comparative approach

Light intensity varies 1 million-fold between night and day, driving the evolution of eye morphology and retinal physiology. Despite extensive research across taxa showing anatomical adaptations to light niches, surprisingly few empirical studies have quantified the relationship between such traits and the physiological sensitivity to light. In this study, we employ a comparative approach in frogs to determine the physiological sensitivity of eyes in two nocturnal (Rana pipiens, Hyla cinerea) and two diurnal species (Oophaga pumilio, Mantella viridis), examining whether differences in retinal thresholds can be explained by ocular and cellular anatomy. Scotopic electroretinogram (ERG) analysis of relative b-wave amplitude reveals 10- to 100-fold greater light sensitivity in nocturnal compared to diurnal frogs. Ocular and cellular optics (aperture, focal length, and rod outer segment dimensions) were assessed via the Land equation to quantify differences in optical sensitivity. Variance in retinal thresholds was overwhelmingly explained by Land equation solutions, which describe the optical sensitivity of single rods. Thus, at the b-wave, stimulus-response thresholds may be unaffected by photoreceptor convergence (which create larger, combined collecting areas). Follow-up experiments were conducted using photopic ERGs, which reflect cone vision. Under these conditions, the relative difference in thresholds was reversed, such that diurnal species were more sensitive than nocturnal species. Thus, photopic data suggest that rod-specific adaptations, not ocular anatomy (e.g., aperture and focal distance), drive scotopic thresholds differences. To the best of our knowledge, these data provide the first quantified relationship between optical and physiological sensitivity in vertebrates active in different light regimes.

Soft transparent graphene contact lens electrodes for conformal full-cornea recording of electroretinogram

Visual electrophysiology measurements are important for ophthalmic diagnostic testing. Electrodes with combined optical transparency and softness are highly desirable, and sometimes indispensable for many ocular electrophysiology measurements. Here we report the fabrication of soft graphene contact lens electrodes (GRACEs) with broad-spectrum optical transparency, and their application in conformal, full-cornea recording of electroretinography (ERG) from cynomolgus monkeys. The GRACEs give higher signal amplitude than conventional ERG electrodes in recordings of various full-field ERG responses. High-quality topographic mapping of multifocal ERG under simultaneous fundus monitoring is realized. A conformal and tight interface between the GRACEs and cornea is revealed. Neither corneal irritation nor abnormal behavior of the animals is observed after ERG measurements with GRACEs. Furthermore, spatially resolved ERG recordings on rabbits with graphene multi-electrode array reveal a stronger signal at the central cornea than the periphery. These results demonstrate the unique capabilities of the graphene-based electrodes for in vivo visual electrophysiology studies.

ELECTRONEGATIVE ELECTRORETINOGRAM IN ACHROMATOPSIA

PURPOSE

To report novel electroretinographic findings in a genetically confirmed case of achromatopsia.

METHODS

A patient with a history of childhood nystagmus, photoaversion, and absent color vision was examined. Electroretinography and fundus examination were performed under anesthesia at the time of corrective surgery for nystagmus. Genomic DNA isolated from peripheral blood was directly sequenced for variations in the CNGA3 and CNGB3 genes.

RESULTS

Ophthalmoscopic examination revealed no distinct abnormalities. Electroretinography obtained under anesthesia at age three years revealed absent photopic responses. The dark-adapted combined responses had reduced b-wave amplitudes resulting in an electronegative configuration. Genetic testing revealed two heterozygous sequence variations present in the coding sequence of the CNGA3 gene (Arg223Trp and Pro372Ser), which have been previously described in the setting of achromatopsia. Sequencing of the patient's parents confirmed that these two variations lie on separate alleles.

CONCLUSION

Novel electroretinography findings in a patient with genetically confirmed achromatopsia are reported. The electronegative configuration in this clinical setting is of unclear etiology; however, it may suggest some component of inner retinal dysfunction.

Electroretinogram evaluation for the treatment of proliferative diabetic retinopathy by short-pulse pattern scanning laser panretinal photocoagulation

Panretinal photocoagulation (PRP) is a standard method for proliferative diabetic retinopathy (PDR) treatment. However, conventional PRP usually significantly damages the retinal structure and vision. Retinal pattern scanning laser (PASCAL) photocoagulation has emerged as a new technique with fewer complications for the treatment of retinal disorders. This study compares the therapeutic effects of short-pulse PASCAL to conventional single-spot PRP for PDR. Fifty-two PDR patients (104 eyes) were randomly assigned into a short-pulse PASCAL-PRP treatment (SP) group and a conventional PRP treatment (TP) group. The best corrected visual acuity (BCVA) and full-field flash electroretinogram (ERG) data were evaluated before and after the two treatments. The BCVA data between before and after the PRP treatments did not show any significant difference. After the PRP treatment, the b-wave amplitude (b-A) in the dark-adapted 3.0 ERG (p = 0.0005) and the amplitude in the light-adapted 3.0 flicker ERG (p = 0.009) were significantly higher in the SP group compared with that of the TP group. In addition, after the PRP treatment, the a-wave implicit time (a-T) of light-adapted 3.0 ERG prolonged significantly in the TP group compared to the SP group. Compared with the parameters before the treatments, the a-A and b-A under dark-adapted 3.0 ERG and the b-A under the light-adapted 3.0 ERG in both TP and SP groups after the treatments decreased significantly (p < 0.05). Short-pulse PASCAL-PRP significantly attenuated partial vision damage compared to conventional PRP, although it still caused limited retinal injury and mild reduction in retinal function. These findings suggest that short-pulse PASCAL-PRP is a promising technique for PDR treatment.

Recording and Analysis of the Human Clinical Electroretinogram

The electroretinogram (ERG) represents the biopotential that is produced by the retina in response to a light stimulus. To date, it remains the best diagnostic tool to objectively evaluate the functional integrity of the normal or diseased retina. In the following pages we briefly review the necessary requirements in order to record and analyze the conventional clinical ERG.

Evaluation of Critical Flicker-Fusion Frequency Measurement Methods for the Investigation of Visual Temporal Resolution

Recent studies highlight the importance of the temporal domain in visual processing. Critical Flicker-Fusion Frequency (CFF), the frequency at which a flickering light is perceived as continuous, is widely used for evaluating visual temporal processing. However, substantial variability in the psychophysical paradigms, used for measuring CFF, leads to substantial variability in the reported results. Here, we report on a comprehensive comparison of CFF measurements through three different psychophysical paradigms: methods of limits; method of constant stimuli, and staircase method. Our results demonstrate that the CFF can be reliably measured with high repeatability by all three psychophysics methods. However, correlations (r = 0.92, p≪0.001) and agreement (Bland Altman test indicated 95% confidence limit variation of ±3.6 Hz), were highest between the staircase and the constant stimuli methods. The time required to complete the test was significantly longer for the constant stimuli method as compared to other methods (p < 0.001). Our results highlight the suitability of the adaptive paradigm for efficiently measuring temporal resolution in the visual system.

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram

PURPOSE

We introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli.

METHODS

This white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.3° diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG.

RESULTS

We show that wnERG recordings are highly repeatable, with good signal-to-noise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ∼1 photopic cd.m-2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash.

CONCLUSION

The wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG.

TRANSLATIONAL RELEVANCE

The white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.

Extracellular H+ fluxes from tiger salamander Müller (glial) cells measured using self-referencing H+-selective microelectrodes

Self-referencing H⁺-selective electrodes were used to measure extracellular H⁺ fluxes from Müller (glial) cells isolated from the tiger salamander retina. A novel chamber enabled stable recordings using H⁺-selective microelectrodes in a self-referencing format using bicarbonate-based buffer solutions. A small basal H⁺ flux was observed from the end foot region of quiescent cells bathed in 24 mM bicarbonate-based solutions, and increasing extracellular potassium induced a dose-dependent increase in H⁺ flux. Barium at 6 mM also increased H⁺ flux. Potassium-induced extracellular acidifications were abolished when bicarbonate was replaced by 1 mM HEPES. The carbonic anhydrase antagonist benzolamide potentiated the potassium-induced extracellular acidification, while 300 μM DIDS, 300 μM SITS, and 30 μM S0859 significantly reduced the response. Potassium-induced extracellular acidifications persisted in solutions lacking extracellular calcium, although potassium-induced changes in intracellular calcium monitored with Oregon Green were abolished. Exchange of external sodium with choline also eliminated the potassium-induced extracellular acidification. Removal of extracellular sodium by itself induced a transient alkalinization, and replacement of sodium induced a transient acidification, both of which were blocked by 300 μM DIDS. Recordings at the apical portion of the cell showed smaller potassium-induced extracellular H⁺ fluxes, and removal of the end foot region further decreased the H⁺ flux, suggesting that the end foot was the major source of acidifications. These studies demonstrate that self-referencing H⁺-selective electrodes can be used to monitor H⁺ fluxes from retinal Müller cells in bicarbonate-based solutions and confirm the presence of a sodium-coupled bicarbonate transporter, the activity of which is largely restricted to the end foot of the cell.NEW & NOTEWORTHY The present study uses self-referencing H⁺-selective electrodes for the first time to measure H⁺ fluxes from Müller (glial) cells isolated from tiger salamander retina. These studies demonstrate bicarbonate transport as a potent regulator of extracellular levels of acidity around Müller cells and point toward a need for further studies aimed at addressing how such glial cell pH regulatory mechanisms may shape neuronal signaling.

Electrophysiological findings show generalised post-photoreceptoral deficiency in macular telangiectasia type 2

BACKGROUND

Photoreceptor damage, reported in single observations, has been suggested to contribute to the disease pathogenesis in macular telangiectasia type 2 (MacTel2). The purpose of this study was to ascertain whether the photoreceptor or post-photoreceptoral function is affected in MacTel2 and could be detected using electrophysiological examination.

METHODS

Thirty-five eyes from 18 patients (15 men, aged 60.1±9.6 years, range 38-77 years) with MacTel2 were included in the study. All patients underwent standard ophthalmic examination followed by pattern electroretinography (PERG) and full-field ERG. The data were compared against 22 normal control subjects (10 men, age 59.83±6.28 years, range 48-76).

RESULTS

Mean PERG P50 amplitude and peak time in patients with MacTel2 did not differ significantly from control values (p>0.2) but P50 amplitude was subnormal in three patients. The mean scotopic rod b-wave amplitude was significantly lower in patients than in healthy controls (p=0.027). A lower dark-adapted 10.0 b-wave (p=0.06) but not a-wave amplitude (p=0.58) was present in patients with MacTel2. Photopic single-flash a-wave and b-wave amplitudes did not differ between patient and control groups (p=0.2 and 0.3), but 30 Hz flicker peak time was significantly later in patients with MacTel2 with no effect on amplitude (p=0.04 and 0.7).

CONCLUSION

Both scotopic (rod system dominated) and photopic ERGs (cone system) are consistent with post-photoreceptoral dysfunction. There was no electrophysiological evidence of dysfunction at the level of the photoreceptor.

Rai1 frees mice from the repression of active wake behaviors by light

Besides its role in vision, light impacts physiology and behavior through circadian and direct (aka ‘masking’) mechanisms. In Smith-Magenis syndrome (SMS), the dysregulation of both sleep-wake behavior and melatonin production strongly suggests impaired non-visual light perception. We discovered that mice haploinsufficient for the SMS causal gene, Retinoic acid induced-1 (Rai1), were hypersensitive to light such that light eliminated alert and active-wake behaviors, while leaving time-spent-awake unaffected. Moreover, variables pertaining to circadian rhythm entrainment were activated more strongly by light. At the input level, the activation of rod/cone and suprachiasmatic nuclei (SCN) by light was paradoxically greatly reduced, while the downstream activation of the ventral-subparaventricular zone (vSPVZ) was increased. The vSPVZ integrates retinal and SCN input and, when activated, suppresses locomotor activity, consistent with the behavioral hypersensitivity to light we observed. Our results implicate Rai1 as a novel and central player in processing non-visual light information, from input to behavioral output.

DOI:http://dx.doi.org/10.7554/eLife.23292.001

The natural retinoprotectant chrysophanol attenuated photoreceptor cell apoptosis in an N-methyl-N-nitrosourea-induced mouse model of retinal degenaration

Retinitis pigmentosa (RP) is an inherited photoreceptor-degenerative disease, and neuronal degeneration in RP is exacerbated by glial activation. Cassia seed (Jue-ming-zi) is a traditional herbal medicine commonly used to treat ocular diseases in Asia. In this report, we investigated the retina-protective effect of chrysophanol, an active component of Cassia seed, in an N-methyl-N-nitrosourea (MNU)-induced mouse model of RP. We determined that chrysophanol inhibited the functional and morphological features of MNU-induced retinal degeneration using scotopic electroretinography (ERG), optical coherence tomography (OCT), and immunohistochemistry analysis of R/G opsin and rhodopsin. Furthermore, TUNEL assays revealed that chrysophanol attenuated MNU-induced photoreceptor cell apoptosis and inhibited the expression of the apoptosis-associated proteins PARP, Bax, and caspase-3. In addition, chrysophanol ameliorated reactive gliosis, as demonstrated by a decrease in GFAP immunolabeling, and suppressed the activation of matrix metalloproteinase (MMP)-9-mediated gelatinolysis. In vitro studies indicated that chrysophanol inhibited lipopolysaccharide (LPS)-induced iNOS and COX-2 expression in the BV2 mouse microglia cell line and inhibited MMP-9 activation in primary microglia. Our results demonstrate that chrysophanol provided neuroprotective effects and inhibited glial activation, suggesting that chrysophanol might have therapeutic value for the treatment of human RP and other retinopathies.

Assessing the Contribution of the Oscillatory Potentials to the Genesis of the Photopic ERG with the Discrete Wavelet Transform

The electroretinogram (ERG) is composed of slow (i.e., a-, b-waves) and fast (i.e., oscillatory potentials: OPs) components. OPs have been shown to be preferably affected in some diseases (such as diabetic retinopathy), while the a- and b-waves remain relatively intact. The purpose of this study was to determine the contribution of OPs to the building of the ERG and to examine whether a signal mostly composed of OPs could also exist. DWT analyses were performed on photopic ERGs (flash intensities: −2.23 to 2.64 log cd·s·m⁻² in 21 steps) obtained from normal subjects (n = 40) and patients (n = 21) affected with a retinopathy. In controls, the %OP value (i.e., OPs energy/ERG energy) is stimulus- and amplitude-independent (range: 56.6–61.6%; CV = 6.3%). In contrast, the %OPs measured from the ERGs of our patients varied significantly more (range: 35.4%–89.2%; p < 0.05) depending on the pathology, some presenting with ERGs that are almost solely composed of OPs. In conclusion, patients may present with a wide range of %OP values. Findings herein also support the hypothesis that, in certain conditions, the photopic ERG can be mostly composed of high-frequency components.