Rodent Hyperglycemia-Induced Inner Retinal Deficits are Mirrored in Human Diabetes.
ABSTRACT: To evaluate the utility of low luminance stimuli to functionally probe inner retinal rod pathways in the context of diabetes mellitus in both rat and human subjects.Inner retinal dysfunction was assessed using oscillatory potential (OP) delays in diabetic rats. Scotopic electroretinograms (ERGs) in response to a series of increasing flash luminances were recorded from streptozotocin (STZ)-treated and control Sprague-Dawley rats after 7, 14, 20, and 29 weeks of hyperglycemia. We then evaluated OP delays in human diabetic subjects with (DR) and without (DM) diabetic retinopathy using the International Society for Clinical Electrophysiology in Vision (ISCEV) standard scotopic protocol and two additional dim test flashes.Beginning 7 weeks after STZ, OP implicit times in diabetic rats were progressively delayed in response to dim, but not bright stimuli. In many diabetic subjects the standard ISCEV dim flash failed to illicit measureable OPs. However, OPs became measurable using a brighter, nonstandard dim flash (Test Flash 1, -1.43 log cd s/m2), and exhibited prolonged implicit times in the DM group compared with control subjects (CTRL).Delays in scotopic OP implicit times are an early response to hyperglycemia in diabetic rats. A similar, inner retinal, rod-driven response was detected in diabetic human subjects without diabetic retinopathy, only when a nonstandard ISCEV flash intensity was employed during ERG testing.The addition of a dim stimulus to standard ISCEV flashes with assessment of OP latency during ERG testing may provide a detection method for early retinal dysfunction in diabetic patients.
Project description:Diabetic retinopathy (DR) is diagnosed clinically by directly viewing retinal vascular changes during ophthalmoscopy or through fundus photographs. However, electroretinography (ERG) studies in humans and rodents have revealed that retinal dysfunction is demonstrable prior to the development of visible vascular defects. Specifically, delays in dark-adapted ERG oscillatory potential (OP) implicit times in response to dim-flash stimuli (<-1.8 log cd · s/m2) occur prior to clinically recognized DR. Animal studies suggest that retinal dopamine deficiency underlies these early functional deficits. In this study, we randomized individuals with diabetes, without clinically detectable retinopathy, to treatment with either low- or high-dose Sinemet (levodopa plus carbidopa) for 2 weeks and compared their ERG findings with those of control subjects (no diabetes). We assessed dim-flash-stimulated OP delays using a novel handheld ERG system (RETeval) at baseline and 2 and 4 weeks. RETeval recordings identified significant OP implicit time delays in individuals with diabetes without retinopathy compared with age-matched control subjects (P < 0.001). After 2 weeks of Sinemet treatment, OP implicit times were restored to control values, and these improvements persisted even after a 2-week washout. We conclude that detection of dim-flash OP delays could provide early detection of DR and that Sinemet treatment may reverse retinal dysfunction.
Project description:To estimate heritability of parameters of human retinal electrophysiology and to explore which parameters change with age.Prospective, classic twin study.Adult monozygotic and dizygotic twin pairs recruited from the TwinsUK cohort.Electroretinogram responses were recorded using conductive fiber electrodes in response to stimuli incorporating standards set by the International Society for the Clinical Electrophysiology of Vision. These parameters were extracted; in addition, photopic negative-response (PhNR; originating from retinal ganglion cells) and i-wave components were extracted from responses to the photopic single flash. Parameter values were averaged from both eyes.Mean values were calculated for the cohort. Correlation coefficients with age were calculated (averaging parameters from both twins from each pair). Coefficients of intrapair correlation were calculated for monozygotic and dizygotic twins. Age-adjusted heritability estimates were derived using standard maximum likelihood structural equation twin modeling.Responses were recorded from 210 participants in total (59 monozygotic and 46 dizygotic twin pairs). Ninety-three percent were women. Mean age for the cohort was 62.4 years (standard deviation, 11.4 years). In general, response amplitudes correlated negatively, and implicit times positively, with age. Correlations were statistically significant (P < 0.05) and moderate or strong (coefficient, >0.35) for the following parameters: scotopic standard and bright-flash a-wave implicit times, photopic 30-Hz flicker and single-flash b-wave implicit times, and PhNR and i-wave implicit times. Intrapair correlations were higher for monozygotic than dizygotic twins, suggesting important genetic influences. Age-adjusted estimates of heritability were significant for all parameters (except scotopic dim-flash b-wave implicit time), ranging from 0.34 to 0.85. Highest estimates were for photopic single-flash a-wave and b-wave amplitudes (0.84 and 0.85, respectively).This study explored heritability of retinal electrophysiologic parameters and included measurements reflecting ganglion cell function. Most parameters showed significant heritability, indicating that genetic factors are important, determining up to 85% of the variance in some cone system response parameters. Scotopic responses tended to show lower heritability (possibly relating to greater rod system susceptibility to environmental factors). Future studies can explore the identity of these genetic factors, improving our understanding of how they shape retinal function.
Project description:The temporal resolution of scotopic vision is thought to be constrained by the signaling kinetics of retinal rods, which use a highly amplified G-protein cascade to transduce absorbed photons into changes in membrane potential. Much is known about the biochemical mechanisms that determine the kinetics of rod responses ex vivo, but the rate-limiting mechanisms in vivo are unknown. Using paired flash electroretinograms with improved signal-to-noise, we have recorded the amplitude and kinetics of rod responses to a wide range of flash strengths from living mice. Bright rod responses in vivo recovered nearly twice as fast as all previous recordings, although the kinetic consequences of genetic perturbations previously studied ex vivo were qualitatively similar. In vivo, the dominant time constant of recovery from bright flashes was dramatically reduced by overexpression of the RGS9 complex, revealing G-protein deactivation to be rate limiting for recovery. However, unlike previous ex vivo recordings, dim flash responses in vivo were relatively unaffected by RGS9 overexpression, suggesting that other mechanisms, such as calcium feedback dynamics that are strongly regulated by the restricted subretinal microenvironment, act to determine rod dim flash kinetics. To assess the consequences for scotopic vision, we used a nocturnal wheel-running assay to measure the ability of wild-type and RGS9-overexpressing mice to detect dim flickering stimuli and found no improvement when rod recovery was speeded by RGS9 overexpression. These results are important for understanding retinal circuitry, in particular as modeled in the large literature that addresses the relationship between the kinetics and sensitivity of retinal responses and visual perception.
Project description:Type 2 diabetic retinopathy is the main cause of acquired blindness in adults. The aim of this work was to examine the retinal function of the sand rat Psammomys obesus as an animal model of diet-induced type 2 diabetes when subjected to a hypercaloric regimen.Hyperglycemia was induced in Psammomys obesus by high caloric diet (4 kcal/g). The visual function of control (n = 7) and diabetic (n = 7) adult rodents were followed up during 28 consecutive weeks with full-field electroretinogram(ERG) recordings evoked to flashes of white light according to the standard protocol of the International Society for Clinical Electrophysiology of Vision protocol (ISCEV).Twenty-eight weeks following the induction of diabetes, results revealed significantly reduced and delayed photopic and scotopic ERG responses in diabetic rats compared to control rats. More specifically, we noted a significant decrease in the amplitude of the dark-adapted 0.01ERG (62%), a- and b-wave amplitudes of the dark-adapted 3.0 ERG (33.6%, 55.1%) and the four major oscillatory potentials components (OP1-OP4) (39.0%, 75.2%, 54.8% and 53.7% respectively). In photopic conditions, diabetic rats showed a significant decrease in a- and b-wave (30.4%, 43.4%), photopic negative response (55.3%), 30 Hz flicker (63.7%), OP1-OP4(51.6%, 61.8%, 68.3% and 47.5% respectively) and S-cone (34.7%). Significantly delayed implicit times were observed for all ERG components in the diabetic animals. Results obtained are comparable to those characterizing the retinal function of patients affected with advanced stage of diabetic retinopathy.Psammomys obesus is a useful translational model to study the pathophysiology of diabetic retinopathy in order to explore new therapeutic avenues in human patients.
Project description:PURPOSE:To characterize the changes found in the electroretinography (ERG) recordings of patients with autosomal dominant neovascular inflammatory vitreoretinopathy and correlate with clinical stages of the disease. METHODS:Retrospective chart review. Bright- and dim-flash full-field scotopic, photopic, and 30-Hz flicker ERGs were obtained according to international standards. The scotopic ERGs were further processed to analyze the oscillatory potential. The patient described in the case report underwent full ERG testing; five patients composed the archival case series data and included scotopic ERG recordings. RESULTS:Stage I autosomal dominant neovascular inflammatory vitreoretinopathy is characterized by a decrease in the b-wave amplitude on scotopic flash ERG and the disappearance of late OPs; however, the a-wave amplitude is normal. In Stage II, attenuation of early OPs and the c-wave are observed in scotopic ERG recordings, but both a- and b-wave amplitudes are unchanged. For patients in Stage III, there is a continued decline of both a- and b-wave amplitudes in scotopic ERG recordings. There was a loss of recordable scotopic ERG response in patients with Stage IV disease. CONCLUSION:Electroretinography may be valuable in determining optimal timing for therapeutic intervention and response before loss of recordable retinal function in CAPN5 vitreoretinopathy.
Project description:<h4>Purpose</h4>To define the relationship between abnormalities in the activation phase of cone phototransduction and the oscillatory potentials (OPs) of the light-adapted electroretinogram in diabetics who have mild or no retinopathy.<h4>Methods</h4>Subjects included 20 non-diabetic controls and 40 type-2 diabetics (20 had no clinically apparent diabetic retinopathy [NDR] and 20 had mild nonproliferative DR). Single flash responses for a series of stimulus retinal illuminances were measured under light-adapted conditions using conventional techniques. The a-waves of the responses were fit with a delayed Gaussian model to derive R<sub>mp3</sub> (maximum amplitude of the massed photoreceptor response) and S (phototransduction sensitivity). OPs were extracted from the responses by conventional band-pass filtering.<h4>Results</h4>Analysis of variance (ANVOA) indicated that both diabetic groups had significant OP amplitude and S reductions compared to the controls, whereas R<sub>mp3</sub> did not differ significantly among the groups. Although log OP amplitude and log R<sub>mp3</sub> were significantly correlated for the control subjects for each flash retinal illuminance (all r?>?0.49, p?<?0.03), log OP amplitude and log R<sub>mp3</sub> were not correlated for either diabetic group for any flash retinal illuminance (all r???0.36, p???0.13). Log OP amplitude and log S were generally not correlated significantly for the control or diabetic groups.<h4>Conclusion</h4>OP amplitude losses do not appear to be related to reduced cone sensitivity in early-stage diabetic retinopathy. This suggests that diabetes may separately affect cone function, as evidenced by cone phototransduction sensitivity losses, and inner-retina function, as evidenced by OP amplitude losses.
Project description:Multiple isoforms of dystrophin (Dp427, Dp260, Dp140, Dp71) are expressed differentially in the central nervous system (CNS) including the retinal layers. Disruption of these protein products is responsible for cognitive dysfunction, electroretinogram (ERG) abnormalities and behavioural disorders in Duchenne muscular dystrophy (DMD). We studied the ocular characteristics and neuropsychiatric profile of 16 DMD boys. The ISCEV standard, full-field flash ERGs were assessed. Intellectual ability and behavioural disturbances were measured. All genotypes were associated with mildly abnormal photopic ERG a:b-wave amplitude ratios. In addition, we identified the following genotype/phenotype correlations: boys with mutations upstream of exon 30 (ie, isolated Dp427 altered expression) showed normal scotopic a:b ratios, abnormal photopic oscillatory potential OP2 and normal scotopic OP2. Conversely, all boys with DMD mutations downstream of exon 30 showed profoundly 'negative' scotopic ERGs (a:b ratios >1). In these patients, the involvement of Dp260 isoform resulted in the absence of slow rod pathway signalling in15?Hz scotopic flicker ERGs. These boys had abnormal scotopic OP2 and normal photopic OP2. Finally, children with mutations also affecting Dp71 were associated with more pronounced electronegative ERGs. When correlating ERGs to neurodevelopmental outcome, we found a positive correlation between negative scotopic ERGs and neurodevelopmental disturbances, and the most severe findings were in boys with Dp71 disruption. These findings suggest a strong association between DMD mutations affecting different DMD isoforms with characteristically abnormal scotopic ERGs and severe neurodevelopmental problems. The role of the ERG as a potential biomarker for dystrophin function in the CNS and response to novel genetic therapies warrants further exploration.
Project description:Purpose:Diabetic retinal neuropathy refers to retinal neural tissue damage occurring before the structural retinal changes of diabetic retinopathy and fulfils many of the criteria for causality for the subsequent vasculopathy. Developing reliable means of measuring neuronal damage in diabetes may be important in efforts to prevent retinopathy of a clinically significant and irreversible stage. This study aimed at systematically assessing current clinical measurements of diabetic retinal neuropathy so that future studies may utilise a consensual battery of tests in studying this poorly understood disease state between a healthy retina and one that is retinopathic. Methods:A systematic search of the medical literature since 1984 was performed on PUBMED and EMBASE, and the evidence supporting each identified method as an indicator for clinically important diabetic retinal neuropathy was graded relatively as compelling, medium, or weak according to criteria assessing its relationship to subsequent diabetic retinopathy, quality of supporting studies, and published reproducibility. Results:The systematic search yielded 6432 results. Subsequent assessment by two independent investigators identified 601 multiple subject studies in humans assessing clinical aspects of the retinal structure, function, or psychophysics in the prediabetic retina. The 933 separate instances of clinical methods assessed as being supported by relatively "compelling" evidence included colour vision changes, flash ERG b-wave latency, flash multifocal b-wave latency, scotopic b-wave and oscillatory potentials in ERG, and contrast sensitivity. Conclusion:The results showed moderately poor quality of extant evidence and indicate the best clinical methods for assessing diabetic retinal neuropathy that remain to be confirmed. This is the first systematic assessment of the medical literature aiming at assessing the breadth and validity of these methods and represents an early step in identifying and developing clinical endpoints for use in trials designed to identify at-risk patients or prevent diabetic retinopathy.
Project description:Cell transplantation is a potential strategy for treating blindness caused by the loss of photoreceptors. Although transplanted rod-precursor cells are able to migrate into the adult retina and differentiate to acquire the specialized morphological features of mature photoreceptor cells, the fundamental question remains whether transplantation of photoreceptor cells can actually improve vision. Here we provide evidence of functional rod-mediated vision after photoreceptor transplantation in adult Gnat1?/? mice, which lack rod function and are a model of congenital stationary night blindness. We show that transplanted rod precursors form classic triad synaptic connections with second-order bipolar and horizontal cells in the recipient retina. The newly integrated photoreceptor cells are light-responsive with dim-flash kinetics similar to adult wild-type photoreceptors. By using intrinsic imaging under scotopic conditions we demonstrate that visual signals generated by transplanted rods are projected to higher visual areas, including V1. Moreover, these cells are capable of driving optokinetic head tracking and visually guided behaviour in the Gnat1?/? mouse under scotopic conditions. Together, these results demonstrate the feasibility of photoreceptor transplantation as a therapeutic strategy for restoring vision after retinal degeneration.
Project description:Reticular pseudodrusen (RPD) could be present not only in the posterior pole but extramacular area also as a confluent morphological pattern. Thus RPD can be classified by the fundus distribution for the assessment of visual prognosis. The electrophysiological function in eyes with reticular pseudodrusen (RPD), showing various fundus distribution were evaluated using full-field electroretinogram (ERG). Retinal distribution of RPD was divided into three types (localized, intermediate, and diffuse) according to the extent of involvement of retinal areas by fundus photograph montages. RPD were present with the diffuse type in 21 eyes (25.6%), with the intermediate type in 30 eyes (36.6%), and with the localized type in 31 eyes (37.8%). The average age was 74.76 ± 4.52 (range, 65-81) years in the diffuse type, 72.47 ± 9.13 (range, 55-91) years in the intermediate type, and 70.26 ± 7.77 (range, 61-89) years in the localized type. The mean amplitudes of the scotopic rod response, scotopic maximal combined response, oscillatory potentials (OP), photopic cone response, and 30Hz cone flicker response were more decreased in the diffuse, intermediate, and localized types in order, except for the photopic cone a-wave response. The diffuse type showed reduced amplitudes of ERG responses than the normal control group under all testing conditions except for the photopic a-wave response, and differences were statistically significant with the age restriction and adjustment methods (Bonferroni-corrected P < 0.05). The mean implicit times of ERG responses were significantly delayed in the diffuse type in the photopic b-wave. (Bonferroni-corrected P < 0.05). Extensive retinal involvement of RPD correlates with severely reduced electrophysiological retinal function. This acquired form of decreased electrophysiological function should be regarded as different from those of hereditary retinal degeneration.