Hz Flicker Research Articles

Sensory dynamics of visual hallucinations in the normal population.

Hallucinations occur in both normal and clinical populations. Due to their unpredictability and complexity, the mechanisms underlying hallucinations remain largely untested. Here we show that visual hallucinations can be induced in the normal population by visual flicker, limited to an annulus that constricts content complexity to simple moving grey blobs, allowing objective mechanistic investigation. Hallucination strength peaked at ~11 Hz flicker and was dependent on cortical processing. Hallucinated motion speed increased with flicker rate, when mapped onto visual cortex it was independent of eccentricity, underwent local sensory adaptation and showed the same bistable and mnemonic dynamics as sensory perception. A neural field model with motion selectivity provides a mechanism for both hallucinations and perception. Our results demonstrate that hallucinations can be studied objectively, and they share multiple mechanisms with sensory perception. We anticipate that this assay will be critical to test theories of human consciousness and clinical models of hallucination.

Comparing DTL microfiber and Neuroline skin electrode in the Mini Ganzfeld ERG.

BackgroundIn infant ERG recordings skin electrodes frequently result in a better compliance. In order to assess the quality of such recordings, we compared the recording characteristics of DTL microfiber and Neuroline surface electrodes using a modified ISCEV protocol in the Mini Ganzfeld ERG.MethodsA prospective cohort study on healthy adult subjects was conducted at the Department of Ophthalmology, University of Basel, Switzerland. Thirty healthy volunteers were tested. The microfiber electrode (DTL Plus Electrode) was placed across the cornea, above the lower eyelid. The Neuroline skin electrode was placed on the surface of the lower lid on the opposite eye. The eye on which each electrode type was placed was randomised.Amplitudes of the rod, standard combined, standard flash cone, light-adapted 3.0 Hz flicker and red cone responses were analysed, as well as their respective implicit times.ResultsBoth electrode recordings showed the same waveform characteristics. Responses with the Neuroline electrode were significantly weaker than those from the DTL electrode. Amplitudes of the rod, standard combined, standard flash cone, light-adapted 3.0 Hz flicker and red cone responses were up to four times larger when recorded with the DTL electrode (p < 0.005, ANOVA). Implicit times of the red cone ERGs were slightly faster for the Neuroline skin electrode recordings (p ≤ 0.039).ConclusionsComparison of full-field ERG recordings with microfiber DTL and Neuroline skin electrodes showed that DTL electrodes produce larger ERGs. Hence, we provide evidence that both electrode types allow successful full-field ERG recording, although separate normative data for both electrodes are necessary.

Abnormal 8-Hz flicker electroretinograms in carriers of X-linked retinoschisis.

To evaluate rod-isolated, cone-isolated, and combined rod and cone flicker electroretinograms (ERGs) as a possible means to identify electrophysiological abnormalities in carriers of X-linked retinoschisis (XLRS). Full-field ERGs were recorded from six carriers of XLRS (aged 34-66years) and eight normally sighted subjects (aged 27-59years) under rod-isolated (ERGR), cone-isolated (ERGC), and combined rod and cone (ERGR+C) conditions. ERGs were obtained using a four-primary LED-based ganzfeld photostimulator and standard recording techniques. The four primaries were modulated sinusoidally in phase to achieve combined rod and cone activation (ERGR+C) or in different phases to achieve ERGR and ERGC by means of triple silent substitution. After 30min of dark adaptation, 8- and 15-Hz ERGR, ERGC, and ERGR+C responses were obtained at a mean luminance level of 24scot.cd/m(2). Standard ISCEV ERGs were also obtained from each subject. The ISCEV and 15-Hz flicker ERGs were generally within the normal range for the carriers. The 8-Hz ERGR, ERGC, and ERGR+C amplitudes were also generally normal. In contrast, the carriers had ERGR, ERGC, and ERGR+C timing abnormalities, with phase advances beyond the range of normal for the ERGR (four carriers), ERGC (four carriers), and ERGR+C (three carriers). Only one carrier had normal 8-Hz responses under all conditions. The 8-Hz ERG timing abnormalities in five of six carriers indicate that retinal function is not necessarily normal in carriers of XLRS. The 8-Hz flicker ERG may be useful for studying retinal function in these individuals.

Features of full field electroretinogram responses in children with early type 1 diabetes

Objective To observe the features of the full field electroretinogram (FF-ERG) in type 1 diabetes (T1D) children without diabetic retinopathy (DR). Methods Retrospective case study. Forty-one T1D children and 25 age-matched normal controls underwent a complete ophthalmic examination, including best-corrected visual acuity, refraction, intraocular pressure, slit lamp, fundus photography, indirect ophthalmoscopy, and spectral domain optical coherence tomography to exclude DR. All FF-ERG tests were performed by an experienced technician. The ERG series includes six protocols: dark-adapted 0.01 ERG (r-b 0.01); dark-adapted 3 ERG (mix-a 3.0, mix-b 3.0); dark-adapted 10 ERG (mix-a 10.0, mix-b 10.0); dark-adapted oscillatory potentials (OPS); light-adapted 3 ERG (c-a 3.0, c-b 3.0); light-adapted 30 Hz flicker (30 Hz FP) ERG. To compare the amplitudes and implicit times of the FF-ERG between the T1D and control group children. Results Compared with the control subjects , the FF-ERG amplitudes decreased and the implicit times increased in T1D. Except for r-b 0.01 (t=-0.228, P>0.05), the amplitudes of other FF-ERGs were all significantly attenuated (t=-1.664, -3.645, -4.324, -6.123, -5.846, -12.9, -14.4, -5.23; P 0.05). Conclusion The FF-ERG amplitudes decreased and implicit times increased in T1D children compared with the control normal subjects. Key words: Diabetes mellitus, type 1; Child; Electroretinography

Characterizing the Retinal Function of Psammomys obesus: A Diurnal Rodent Model to Study Human Retinal Function

ABSTRACTPurpose: To compare the retinal function of a diurnal murid rodent, Psammomys obesus, with that of Wistar albino rat and human subjects.Materials and methods: Adult Psammomys obesus were captured and transferred to the animal facilities where they were maintained at 25°C with standard light/dark cycles and natural halophilic plants, rich in water and mineral salts. Standard full-field photopic and scotopic electroretinograms were obtained.Results: The right eye of all animals displayed well detectable and reproducible scotopic and photopic electroretinogram (ERG) responses. Results were compared with those obtained from human subjects and Wistar rats. ERG measurement showed that the amplitudes of scotopic responses in Psammomys obesus are quite similar to those of human subjects. The amplitude of the photopic a-wave was comparable to that of humans and six times higher than that of the albino rat. The amplitudes of photopic b-wave, photopic oscillatory potentials (OPs), and 30 Hz flicker were all markedly larger in Psammomys obesus compared to those obtained from human subjects and Wistar rats. Furthermore, like the human photopic ERG, the photopic ERG of Psammomys obesus also includes prominent post b-wave components (i.e. i- and d-waves) while the ERG of Wistar rats does not.Conclusions: Our results suggest that the retinal function of Psammomys obesus, especially the cone-mediated function, shares several features with that of human subjects. We believe that Psammomys obesus represents an interesting alternative to study the structure and function of the normal and diseased retina in a human-like rodent model of retinal function.

Full-field electroretinogram in autism spectrum disorder.

To explore early findings that individuals with autism spectrum disorder (ASD) have reduced scotopic ERG b-wave amplitudes. Light-adapted (LA) and dark-adapted (DA) ERGs were produced by a range of flash strengths that included and extended the ISCEV standard from two subject groups: a high-functioning ASD group N = 11 and a Control group N = 15 for DA and N = 14 for LA ERGs who were matched for mean age and range. Flash strengths ranged from DA -4.0 to 2.3 log phot cd s m(-2) and LA -0.5 to 1.0 log phot cd s m(-2), and Naka-Rushton curves were fitted to DA b-wave amplitude over the first growth limb (-4.0 to -1.0 log phot cd s m(-2)). The derived parameters (V max, K m and n) were compared between groups. Scotopic 15-Hz flicker ERGs (14.93 Hz) were recorded to 10 flash strengths presented in ascending order from -3.0 to 0.5 log Td s to assess the slow and fast rod pathways, respectively. LA 30-Hz flicker ERGs, oscillatory potentials (OPs) and the responses to prolonged 120-ms ON-OFF stimuli were also recorded. The ISCEV LA b-wave amplitude produced by 0.5 log phot cd s m(-2) was lower in the ASD group (p < 0.001). Repeated measures ANOVA for the LA b-wave amplitude series forming the photopic hill was significantly (p = 0.01) different between groups. No group differences were observed for the distributions of the time to peaks of LA a-wave, b-wave or the photopic negative responses (phNR) (p > 0.08) to the single flash stimuli, but there was a significant difference in the distribution for the LA b-wave amplitudes (corrected p = 0.006). The prolonged 120-ms ON responses were smaller in the ASD group (corrected p = 0.003), but the OFF response amplitude (p > 0.6) and ON and OFF times to peaks (p > 0.4) were similar between groups. The LA OPs showed an earlier bifurcation of OP2 in the younger ASD participants; however, no other differences were apparent in the OPs or 30-Hz flicker waveforms. DA b-wave amplitudes fell below the control 5th centile of the controls for some individuals including four ASD participants (36 %) at the 1.5 log phot cd s m(-2) flash strength and two (18%) ASD participants at the lower -2 log phot cd s m(-2) flash strength. However, across the 13 flash strengths, there were no significant group differences for b-wave amplitude's growth (repeated measures ANOVA p = 0.83). Nor were there any significant differences between the groups for the Naka-Rushton parameters (p > 0.09). No group differences were observed in the 15-Hz scotopic flicker phase or amplitude (p > 0.1), DA ERG a-wave amplitude or time to peak (p > 26). The DA b-wave time to peak at 0.5 log phot cd s m(-2) was longer in the ASD group (p = 0.04). Under LA conditions, the b-wave is reduced across the ASD group, along with the ON response of the prolonged flash ERG. Some ASD individuals also show subnormal DA ERG b-wave amplitudes. These exploratory findings suggest there is altered cone-ON bipolar signalling in ASD.

Flicker Sensitivity in Normal Aging--Monocular Tests of Retinal Function at Photopic and Mesopic Light Levels.

Aging can affect many aspects of visual performance. In general, the effects become more significant in those older than 40 to 50 years, with increased intersubject variability and stronger dependence on ambient illumination. This study aimed to establish how healthy aging of the retina affects the detection of 15-Hz flicker under photopic and mesopic lighting. We investigated 71 participants aged 20 to 75 years. Thresholds were measured for detection of 15-Hz flicker at the fovea (0°) and at an eccentricity of 4° in each of the four quadrants. The background luminance ranged from 0.6 to 60 cd/m(2) and pupil size was measured continuously. Participants were excluded if they had signs/history of ocular disease, substantial interocular differences in flicker thresholds, or were unable to detect 100% flicker modulation in the high mesopic range. Mesopic and photopic flicker thresholds were used to calculate an index, the health of the retina index, to determine the limits of flicker sensitivity in healthy aging. Log flicker thresholds changed bilinearly with age; they remained stable until 40 to 50 years, with a linear decline with increasing age. This bilinear pattern of the change in flicker thresholds with age is consistent across photopic and mesopic light levels. The health of the retina index captures the lowest threshold, usually obtained under photopic conditions, as well as the loss of flicker sensitivity with decreasing light level. The established limits of healthy aging may benefit from future studies in patients with ocular hypertension and/or glaucoma that are known to experience loss of flicker sensitivity.

Antioxidant supplementation increases retinal responses and decreases refractive error changes in dogs.

The objective of the study was to examine whether a nutritional antioxidant supplementation could improve visual function in healthy dogs as measured by electroretinography (ERG) and autorefraction. A total of twelve Beagles, 6 to 8 years of age, with normal eyes upon indirect ophthalmoscopy and slit lamp biomicroscopy, were age and sex matched and randomly assigned to receive a feeding regimen for 6 months with or without a daily antioxidant supplementation. Portable, mini-Ganzfeld ERG and a Welch Allyn hand-held autorefractor were used to test retinal response and refractive error in the dogs at baseline and at the end of the supplementation period. All ERG a-wave amplitudes obtained were increased in the treatment group compared with those of dogs in the control group, with significant improvements in the scotopic high and photopic single flash cone ERG responses (P < 0·05 for both). For the b-wave amplitudes, all responses were similarly increased, with significant improvements in responses for the scotopic high light intensity stimulation (P < 0·05), and for photopic single flash cone and 30 Hz flicker (P < 0·01 for both) recordings. Change in refractive error was significantly less in the treatment group compared with that of the control group during the 6-month study (P < 0·05). Compared with the control group, the antioxidant-supplemented group showed improvement to varying degrees for retinal function and significantly less decline in refractive error. Dogs, like humans, experience retinal and lens functional decline with age. Antioxidant supplementation as demonstrated may be beneficial and effective in the long-term preservation and improvement of various functions of the canine eye.

Expression and role of Egr-1 gene in retina of flicker light-induced eyes in mice

Background Flicker light can induce myopia, but its mechanism remains unclear. As one of immediate early genes, early growth response-1(Egr-1) gene can generate rapid response to visual stimulation, however, its effect on the formation and development of myopia is below understood. Objective This study was to investigate the dynamic expression of Egr-1 gene in retinas of flicker light-induced eyes (FL) and compare the results with form deprived eyes (FD). Methods One hundred and fifty 28-day-old C57BL/6J mice were randomly assigned to the normal control group, FD group and FL group. The right eyes of mice were occluded with a semitransparent hemispherical thin plastic shell for 2 weeks in the FD group, and the right eyes of mice were stimulated by 2 Hz flicker light for 2 weeks in the FL group, and then the mice were fed in the normal light environment for 1 week. The refractive state and axial length of the model eyes were measured by murine-specific eccentric infrared photorefraction and A-scan ultrasonography before modeling and 1 hour, 1 day, 1 week, 2 weeks after modeling as well as 1 week after termination, respectively. The mice were sacrificed in above-mentioned time points to isolate the retinas. The expressions and location of Egr-1 protein and mRNA in the retinas were detected by Western blot, and reverse transcription PCR (RT-PCR) and immunochemistry. The expressions of Egr-1 markers, neuron and protein kinase C (PKC)-α, in the retinas were assayed by using immunofluorescence. The care and use of the animals followed the administration regulations for experimental animals of Jiangsu Province. Results Two weeks after modeling, the refraction of the FL group was (0.32±0.14)D, which was significantly lower than (-0.66±0.43)D in the FD group (t=6.78, P=0.00). One hour after modeling, The expression levels of Egr-1 mRNA in mouse retinas were 0.626±0.044 and 0.695±0.058 in the FD group and FL group, which were significantly declined in comparison with 1.009±0.089 of the normal group (t=14.81, P=0.01; t=9.15, P=0.03). In 2 weeks after modeling, the expression levels of Egr-1 mRNA were still lower in the FD group and FL group compared with the normal group (all at P<0.05). However, the expression levels were significantly elevated in the FD group and FL group compared with the normal group (t=4.13, P=0.01; t=4.26, P=0.01) at 1 week after termination. Western blot showed a dynamic decrease in the expressions of Egr-1 protein with lapse of time in the FD group and FL group with the lowest expressing level in the second week after modeling. In 1 week after termination of modeling, the expressing level was raised in the FD group or the FL group, but it was still lower than that in the normal group (t=6.32, P=0.00; t=5.45, P=0.01). Egr-1 protein was mainly expressed in the retinal ganglion cell (RGC) layer, inner nuclear layer and photoreceptor layer in the normal mice, and the expression intensity was obviously weaker in the FD mice and FL mice 2 weeks after modeling. However, the expression was enhanced in 1 week after termination of modeling. Neuron and PKC-α were strongly expressed in the RGCs and bipolar cells in the normal mice. Conclusions The eyes show a myopic trend after induce of flicker light in B6 mice. The expression level of Egr-1 gene in the retina down-regulates with the reduce of refraction in FL eyes, and its dynamic expressing change is consistent between the FD eyes and FL eyes. Key words: Refraction, ocular/physiology; Myopia; Early growth response protein 1/genetics; Sensory deprivation; Light; Mice, inbred C57BL; Disease model, animal

Photopic full-field electroretinography and optical coherence tomography in type 1 diabetic retinopathy.

PurposeThe purpose of this study was to evaluate the role of photopic full-field electroretinography (ERG) and retinal thickness measurements by spectral-domain optical coherence tomography (SD-OCT) in the assessment of disease severity in type 1 diabetic retinopathy.MethodsA population-based cohort of 151 patients with type 1 diabetes underwent a complete ophthalmic examination, including photopic full-field ERG and SD-OCT for retinal thickness measurements. Stereoscopic fundus photographs were taken according to the Early Treatment Diabetic Retinopathy Study protocol, and the classification of diabetic retinopathy was based on the International Clinical Diabetic Retinopathy Disease Severity Scale. Associations between photographically determined retinopathy level, b-wave amplitude and peak time of the photopic single-flash and 30-Hz flicker ERG, and central retinal thickness parameters were evaluated.ResultsFor all ERG measurements, the amplitude decreased and peak time increased with progression of the disease, but these associations lost statistical significance after adjusting for age and excluding laser-treated patients. Mean retinal thickness was significantly associated with the b-wave amplitude of photopic single-flash and 30-Hz flicker responses (r2 = 0.08, p = 0.006; and r2 = 0.05, p = 0.025, respectively), but revealed no association with retinopathy level.ConclusionsPhotopic full-field ERG and SD-OCT-derived retinal thickness parameters have limited clinical value in the staging of diabetic retinopathy. However, thinning of the central retina leads to significant functional impairment and may reflect an ongoing neurodegenerative process in the retinal tissue.

Effect of oral photochemotherapy (8-methoxypsoralen + UVA) on the electrophysiologic function of retina

Context: Since we had observed electroretinographic (ERG) abnormalities in some patients undergoing photochemotherapy with normal eye examination, we decided to investigate the effects of this therapy on retinal function.Objective: To investigate the effects of oral photochemotherapy (8-methoxypsoralen + Ultraviolet-A) on electrophysiologic function of retina.Materials and methods: Patients with vitiligo, psoriasis or eczema were enrolled. Patients with any abnormal eye exam or a positive drug or family history for retinal disease were excluded. Baseline standard ERG was provided with the RETIport32 device. The second ERG was performed 6 months after the first and at least 1 week after the last photochemotherapy session (mean number of sessions: 45 ± 11). The outcome measures were changes in rod response, standard combined response, single-flash cone response, 30-Hz flicker (N1-P1) and oscillatory potentials amplitudes.Results: Forty patients were enrolled; 20 of them (mean age: 31.1 ± 12 years) completed the study. The mean rod response b-wave amplitude decreased from 88.9 ± 47.5 to 86.4 ± 36.6 and standard combined response b-wave amplitude decreased from 266.52 to 261.85 µV (p = 0.422 and p = 0.968, respectively) and the standard combined response a-wave amplitude increased from 155.4 ± 40.0 at baseline to 165.1 ± 48.4 in the follow-up ERG (p = 0.092). The mean single-flash cone response a-wave amplitude decreased insignificantly in the follow-up ERG trace (34.5 ± 13.7 and 29 ± 15.4, respectively, p = 0.242). The mean single-flash cone response b-wave amplitude showed an insignificant increase (p = 0.087). The amplitudes of 30-Hz flicker wave and oscillatory potentials did not change significantly in the follow-up ERG (p = 0.551 and p = 0.739, respectively).Conclusion: Since no significant change in ERG traces was observed, oral photochemotherapy seems safe for retinal electrophysiologic function.

Early adaptive response of the retina to a pro-diabetogenic diet: Impairment of cone response and gene expression changes in high-fructose fed rats

The lack of plasticity of neurons to respond to dietary changes, such as high fat and high fructose diets, by modulating gene and protein expression has been associated with functional and behavioral impairments that can have detrimental consequences. The inhibition of high fat-induced rewiring of hypothalamic neurons induced obesity. Feeding rodents with high fructose is a recognized and widely used model to trigger obesity and metabolic syndrome. However the adaptive response of the retina to short term feeding with high fructose is poorly documented. We therefore aimed to characterize both the functional and gene expression changes in the neurosensory retina of Brown Norway rats fed during 3 and 8 days with a 60%-rich fructose diet (n = 16 per diet and per time point). Glucose, insulin, leptin, triacylglycerols, total cholesterol, HDL-cholesterol, LDL-cholesterol and fructosamine were quantified in plasma (n = 8 in each group). Functionality of the inner retina was studied using scotopic single flash electroretinography (n = 8 in each group) and the individual response of rod and cone photoreceptors was determined using 8.02 Hz Flicker electroretinography (n = 8 in each group). Analysis of gene expression in the neurosensory retina was performed by Affymetrix genechips, and confirmed by RT-qPCR (n = 6 in each group). Elevated glycemia (+13%), insulinemia (+83%), and leptinemia (+172%) was observed after 8 days of fructose feeding. The cone photoreceptor response was altered at day 8 in high fructose fed rats (Δ = 0.5 log unit of light stimulus intensity). Affymetrix analysis of gene expression highlighted significant modulation of the pathways of eIF2 signaling and endoplasmic reticulum stress, regulation of eIF4 and p70S6K signaling, as well as mTOR signaling and mitochondrial dysfunction. RT-qPCR analysis confirmed the down regulation of Crystallins, Npy, Nid1 and Optc genes after 3 days of fructose feeding, and up regulation of End2. Meanwhile, a trend towards an increased expression of αA- and αB-crystallin proteins was observed at day 8. Our results are consistent with early alterations of the functioning and gene expression in the retina in a pro diabetogenic environment.

Peripheral retinal function assessed with 30-Hz flicker seems to improve after treatment with Lucentis in patients with diabetic macular oedema.

To evaluate the influence of ranibizumab on the multifocal electroretinogram (Mf-ERG), full-field electroretinogram (Ff-ERG) and optical coherence tomography (OCT) in diabetic eyes (n = 20) with macular oedema. In 20 eyes (20 diabetic subjects) with no or background diabetic retinopathy and macular oedema (age 65.7 ± 9.8 years, duration 16.5 ± 10.0 years), the change in ETDRS letters, Mf-ERG, Ff-ERG and OCT was analysed, at baseline, 4 weeks after the first injection, (just before the second injection), and 4 weeks after the last injection with ranibizumab. From baseline, mean BCVA improved from 64.0 ± 10.0 ETDRS letters to 75.0 ± 7.3 ETDRS letters (p = 0.005) 1 month after the last injection. Mean OCT thickness reduced after the first injection from 418 ± 117 to 311 ± 126 µm; (p = 0.001) and to 302 ± 74 µm after the third injection. Mf-ERG demonstrated in the innermost three rings a shorter implicit time after the first injection with p values of 0.002, 0.005 and 0.017, respectively. After the third injection, implicit time was prolonged to almost the original levels. Cone implicit time with 30-Hz flicker improved significantly between baseline (35.5 ± 3.6 ms) and final follow-up (34.6 ± 3.1 ms) (p = 0.04). Though the central retinal thickness was reduced after three injections of ranibizumab and the subjects gained a mean of 11 ETDRS letters, there was no significant change in amplitude or implicit time in Mf-ERG. The shortened 30-Hz flicker implicit time might imply that ranibizumab has no negative impact on the entire peripheral cone function, but can improve it instead.

Rod and cone contributions to the dark-adapted 15-Hz flicker electroretinogram.

To evaluate rod and cone contributions to the dark-adapted 15-Hz flicker electroretinogram (ERG) across a broad range of stimulus luminances by comparing rod-isolating (ERGR), cone-isolating (ERGC), and non-receptor-specific (ERGR+C) responses. Dark-adapted, full-field 15-Hz ERGs were obtained from four normally sighted subjects (ages 29-36years) using a four-primary LED-based stimulating system. The primaries were either modulated sinusoidally in phase (ERGR+C) or were modulated in counter-phase to achieve rod isolation (ERGR) or cone isolation (ERGC) by means of triple silent substitution. Measurements were made for a broad range of luminances (-2.5 to 1.8 log scot. cd/m(2) in 0.2 log unit steps). Fourier analysis was used to obtain the amplitude and phase of the fundamental response component at each stimulus luminance. Stimulus luminance had different effects on response amplitudes and phases under the three paradigms. Specifically, ERGC amplitude and phase increased monotonically as luminance increased. The effects on ERGR+C and ERGR were complex: ERGR+C and ERGR amplitude was small and the phase decreased for low luminances, whereas amplitude and phase increased sharply at moderate luminances. For high luminances, ERGR+C amplitude and phase increased, whereas ERGR amplitude decreased and phase was approximately constant. At low luminances, the ERGR+C and ERGR functions can be attributed to interactions between two rod pathways. At high luminances, the functions can be accounted for by interactions between rod and cone pathways (ERGR+C) or rod insensitivity (ERGR). The ERGR paradigm minimizes cone intrusion, permitting assessment of rod function over a large range of luminance levels.

Sildenafil-induced reversible impairment of rod and cone phototransduction in monkeys.

To investigate functional alteration of the retina induced by sildenafil in monkeys. Sildenafil was administered intravenously to cynomolgus monkeys at dose levels of 0, 1, 3, and 10 mg/kg, and standard full-field electroretinograms (ERGs) were recorded. The rod and cone a-waves in response to high-intensity flashes were also analyzed by the a-wave fitting model (a-wave analysis). Additionally, the photopic negative responses were recorded. Sildenafil at 3 mg/kg or more induced the following alterations in the standard full-field ERGs immediately after dosing: delayed b-wave in the rod response; delayed a-wave in the combined rod-cone response; and attenuated b-waves in the single-flash cone response and in the 30 Hz flicker. Additionally, the following changes were observed in the 10 mg/kg group: attenuated b-wave in the rod response; attenuated a-wave and delayed b-wave in the combined rod-cone response; delayed oscillatory potentials; and attenuated and delayed a-wave in the single-flash cone response. In the a-wave analysis immediately after dosing, sildenafil selectively decreased the sensitivity parameter (S) in the cone a-wave at 3 mg/kg, and in both the rod and cone a-waves at 10 mg/kg. The S value was highly correlated with plasma sildenafil concentration. The above changes fully recovered 24 hours after dosing. Sildenafil produced reversible impairment of the rod and cone phototransduction in monkeys. Meanwhile, involvement of the postreceptoral retinal components was suggested. These findings contribute to the clarification of sildenafil-induced visual disturbances. It is suggested that the photoreceptors are predominantly, but not exclusively, affected in the retina of humans with sildenafil-induced visual disturbances.

Variability of Normal Values of Electroretinogram Parameters Due to Aging in Healthy Individuals.

Aim- To find normal values of implicit time and amplitudes of full-field electroretinogram and to determine their changes with age in healthy Romanian subjects. Material and Methods- The prospective study included 59 healthy subjects aged between 20 and 80 years old; in the end, we had valid ERG recordings for all tests from 54 subjects. All of the participants underwent full-field ERG, recorded with Metrovision MonPack One system. The implicit times and amplitudes were analyzed for a and b waves in dark-adapted 0.01 ERG, dark-adapted 3.0 ERG, dark-adapted oscillatory potentials, light-adapted 3.0 ERG, and 30Hz flicker ERG according to International Society for Clinical Electrophysiology of Vision (ISCEV) protocols. Results- ERG latency values were bigger in subjects above 50 years old than in younger subjects for b wave in dark adapted 0.01, dark adapted 3.0, light adapted 3.0 and dark adapted 3.0 flicker and for a wave in dark adapted 0.01 and dark adapted 3.0 ERG. There was no significant difference in latency values for dark adapted 3.0 oscillatory potentials between young and old subjects. Because of increased variability, we could not prove that observed differences for amplitudes held statistical significance. Conclusions- This study proves there is a major loss in retinal activity due to aging, most of it being caused by the rod cells delayed response. Also, oscillatory potentials do not seem to be affected by age, and could prove a valuable test to investigate for changes in patients with Diabetes mellitus.

A Case Presentation Emphasizing the Value of Full-field ERG in Retinal Dystrophies.

ABSTRACT: Purpose: A case presentation is used to discuss the value of full-field ERG in the diagnosis of cone-rod dystrophy. Case report: A 49 year old female patient known with amblyopia and myopic astigmatism since childhood, visited us complaining of decreased visual acuity and photophobia. Her BCVA was 0.6 in the RE and 0.4 in the LE. The fundus examination revealed normal colored and sharply limited papilla, normal macula and narrower vascularization. The Ishihara test was 10/15 in both eyes. The fundus autofluorescence and optical coherence tomography were normal. The DA 3 ERG was decreased and slightly delayed as well as the DA 0.01 ERG. Regarding the cone response, the LA 3.0 and 30 Hz flicker ERG were markedly reduced and delayed. The ERG findings indicated cone-rod dystrophy. At the 8 years follow-up examination, the BCVA decreased to 0.4 and 0.2 in the right and left eye, respectively, the Ishihara test was 1/15 in both eyes and the fundus examination showed a macula with no reflex, otherwise no changes compared to the first examination. The fundus autofluorescence and OCT were still normal. The ERG showed a much decreased and delayed rod response compared to the first examination, while the cone response was undetectable. Conclusion: Our case demonstrates the importance of standard full-field ERG in diagnosing CRD. The Full-field ERG responses were decreased and delayed, or even undetectable, while morphological examinations were still unchanged.

Electrophysiolocal findings in Mohr-Tranebjærg syndrome

Mohr-Tranebjaerg syndrome (MTS) is an X-liked recessive rare syndrome also known as deafness-dystonia syndrome. The severity of the symptoms may vary, but they progress usually to severe deafness and dystonia and sometimes they are accompanied by cortical deterioration of vision and mental deterioration. The purpose of this paper is to illustrate a very interesting case of Mohr-Tranebjaerg syndrome. A 24-year-old italian man with Mohr-Tranebjaerg syndrome underwent full field electroretinography (ERG) and visual evoked potentials (VEPs). Fundus examination showed apparently normal retina with pallor of the optic disc. Pattern reversal VEP and flash VEP responses were non-recordable. ERG showed amplitude reduction of the fotopic, scotopic and 30 Hz flicker responses revealing generalized retinal dysfunction with reduction of cone and rod responses. The progressive neurodegeneration in Mohr-Tranebjaerg syndrome can be also associated with a retinal degeneration.

Normal clinical electroretinography parameters for poodle, Labrador retriever, Thai ridgeback, and Thai Bangkaew.

The purpose of the present study was to establish normal electroretinogram (ERG) parameters using 56 normal eyes of four dog breeds common in Thailand: poodle, Labrador retriever, Thai ridgeback, and Thai Bangkaew. Standard ERG findings were bilaterally recorded using a handheld multi-species ERG unit with an ERG-jet lens electrode for 28 dogs under preanesthesia with diazepam, anesthesia with propofol, and anesthesia maintenance with isoflurane. There were significant differences in the mean values of ERG amplitudes and implicit times among the four dog breeds (p < 0.05) except for the b-wave implicit time of the photopic 30 Hz flicker response with 3 cd.s/m2 (p = 0.610). Out of the four breeds, Thai Bangkaew had the longest implicit time (p < 0.001) of scotopic low intensity responses, b-wave of scotopic standard intensity responses (3 cd.s/m2), a-wave of the higher intensity response (10 cd.s/m2), and a-wave of the photopic single flash response (3 cd.s/m2). For the b/a ratio, only the ratio of the Cone response was significantly different among the different breeds. In this summary, normal ERG parameters for four dog breeds were reported. Data from the investigation supported the hypothesis that determination of breed-specific limits of normality for ERG responses is necessary for individual clinics and laboratories.

Visual Electrodiagnostic Testing in Birdshot Chorioretinopathy.

Birdshot chorioretinopathy (BSCR) is a rare form of autoimmune posterior uveitis that can affect the visual function and, if left untreated, can lead to sight-threatening complications and loss of central vision. We performed a systematic search of the literature focused on visual electrophysiology studies, including electroretinography (ERG), electrooculography (EOG), and visual evoked potentials (VEP), used to monitor the progression of BSCR and estimate treatment efficacy. Many reports were identified, including using a variety of methodologies and patient populations, which makes a direct comparison of the results difficult, especially with some of the earlier studies using nonstandardized methodology. Several different electrophysiological parameters, like EOG Arden's ratio and the multifocal ERG response densities, are reported to be widely affected. However, informal consensus emerged in the past decade that the full-field ERG light-adapted 30 Hz flicker peak time is one of the most sensitive electrophysiological parameters. As such, it has been used widely in clinical trials to evaluate drug safety and efficacy and to guide therapeutic decisions in clinical practice. Despite its wide use, a well-designed longitudinal multicenter study to systematically evaluate and compare different electrophysiological methods or parameters in BSCR is still lacking but would benefit both diagnostic and therapeutic decisions.