Measurement of the oscillatory potentials of the electroretinogram in the domains of frequency and time

The dark-adapted and light-adaped electroretinograms of 13 subjects with 23 normal eyes were analyzed by means of Fourier spectrum. The oscillatory potentials in the time domain were filtered out from the electroretinogram after a corresponding bandpass was given in the frequency domain. The coefficient of variation of total power, dominant power and dominant frequency of the isolated oscillatory potentials in the frequency domain, summed amplitudes and area of the isolated oscillatory potentials, each amplitude and implicit time of the first four major oscillatory potential wavelets in the time domain were compared. The implicit time showed the smallest coefficient of variation; summed amplitudes of OP1 to OP4 showed smaller coefficients of variation than those of the area, the amplitude of each oscillatory potential wavelet, dominant frequency and dominant and total power. The coefficient of variation of these measurement parameters in light-adapted electroretinograms was smaller than those in dark-adapted electroretinograms.Abbreviations CV coefficient of variation - OP oscillatory potential     

Electroretinographic oscillatory potentials in diabetic retinopathy

The oscillatory potentials of the electroretinogram in dark and light adaptation were evaluated by Fourier transform in 87 diabetics and 74 age-matched controls. The study consisted of four groups: normal control, no observable diabetic retinopathy, background diabetic retinopathy and proliferative diabetic retinopathy. A reduction in the amplitude of each oscillatory potential, the summed amplitudes, the area and the total power of the oscillatory potentials as well as delayed implicit time of each oscillatory potential peak in dark and light adaptation could be found in patients with background diabetic retinopathy and proliferative diabetic retinopathy. The amplitude of oscillatory potential 4 in dark adaptation and the total power of the oscillatory potentials in light adaptation seemed to be affected in patients with no observable diabetic retinopathy. The implicit time of oscillatory potential 2 in dark adaptation was valuable to distinguish between patients with no observable diabetic retinopathy and background diabetic retinopathy.Abbreviations NC normal control - NDR no observable diabetic retinopathy - BDR background diabetic retinopathy - PDR proliferative diabetic retinopathy     

Oscillatory potentials and the b-Wave: Partial masking and interdependence in dark adaptation and diabetes in the rat

Background Diabetes inhibits dark adaptation and both processes alter the electroretinogram (ERG) in similar ways. This study aimed to investigate the relationship between oscillatory potentials (OPs) and the b-wave during dark adaptation and to determine if this relationship changes during the development of diabetes. Methods Twenty-one rats were assigned to adaptation, control and diabetic groups. Rats were dark adapted for periods between 20 minutes and 4 hours, and ERGs recorded. Diabetes was induced with streptozotocin, and ERGs measured after 3, 6, 9 and 12 weeks after injection. Results Increasing periods of dark adaptation led to a logarithmic increase in the amplitude of the b-wave and the OPs. This was accompanied by a decrease in the peak times of the OPs and b-wave. Total OP amplitude and b-wave amplitude were linearly related, allowing an empirical OP constant to be developed to describe the relationship between the two parameters. Diabetes led to a progressive decrease in the amplitude and increase in the peak time of all waves. The OP constant decreased in a linear fashion with increasing duration of diabetes. Conclusions It is argued that OP masking of the b-wave could explain previous inconsistencies in reported ERG changes in diabetes and that a slowing of dark adaptation does not account for these ERG changes. The report concludes that the OPs and b-wave amplitudes and latencies are intimately related in the normal retina and that this correlation is lost predictably during the development of diabetes.     

Light adaptation of the human photopic oscillatory potentials: Influence of the length of the dark adaptation period

Photopic electroretinograms recorded immediately after a period of dark adaptation show a regular increase in amplitude with time spent in light. The retinal mechanisms at the origin of this light adaptation effect remain obscure. The purpose of this study was to investigate the duration of the dark adaptation period needed to produce an optimal light adaptation effect as demonstrated by photopic oscillatory potential recordings. Our results indicate that the light adaptation effect can be separated into two distinct processes. The first one, activated early in the dark adaptation process, reduces the amplitude of the fourth oscillatory potential to 32% of control after less than 5 min of dark adaptation, while the second process, activated after more than 10 min of dark adaptation, appears to impact solely the amplitude of the earlier oscillatory potentials 2 and 3. Our results suggest that the light adaptation effect is mediated by two distinct retinal pathways or mechanisms.Abbreviations DA dark adaptation - LAE light adaptation effect     

Correlation of an exercise-induced increase in systemic circulation with neural retinal function in humans

Although the effects of physical exertion on intraocular pressure and systemic blood pressure are well established, the retinal response to such physiologic stress has not been examined. We studied the effect of short-term intense exercise on the principal waves in the scotopic and photopic flash electroretinograms, as well as the lower-amplitude oscillatory potentials. Sixteen healthy volunteers between 20 and 30 years of age participated in this experiment. The electroretinograms and oscillatory potentials were recorded with a Nicolet CA-1000 clinical averager, using DTL-type fiber electrodes. All retinal potentials were taken immediately before and after a minimum 20-min period of stationary bicycling that increased the heart rate to about 140 beats per minute. The electroretinograms were recorded from eyes with dilated pupils, 10 min after white-light adaptation of the right eye, and 30 min after dark adaptation of the left eye. Red flashes and dim white flashes were used to elicit photopic and scotopic electroretinograms, respectively. While no changes were recorded for any of the electroretinogram components recorded under photopic conditions, the amplitude of OP5 was decreased and the implicit time of OP4 was delayed after exercise for scotopic conditions. We concluded that exercise caused component-specific changes in the scotopic oscillatory potentials. Since it is well known that oscillatory potentials are vulnerable to ischemia, scotopic oscillatory potentials may be used as simple noninvasive indices of the reactivity of the retinal vascular autoregulatory system during exercise.     

Oscillatory potential changes related to stimulus intensity and light adaptation

The oscillatory potentials (OPs) are a series of subcomponents of the flash ERG which probably originate in the inner plexiform layer of the retina. Abnormal OPs in various forms of retinopathy include central retinal vein occlusion, congenital stationary night blindness, and diabetic retinopathy. We investigated the effects of stimulus intensity and light adaptation on the OP components identified in our laboratory. OPs were recorded from 20 adult eyes to full-field ganzfeld stimulation at four stimulus intensities from 12 to 62cd/m². Stimulus flashes were superimposed over a steady background luminance in the ganzfeld. Four background luminances were used over a 3-log unit range from mesopic to photopic levels. Peak-to-peak amplitude and peak implicit time measures of the OPs were obtained. Latency-intensity functions were derived for each of the four OP components at each light-adaptation level. These latency-intensity functions revealed similar curve fitting slopes for all OP subcomponents at lower light-adaptation levels. At higher levels of light adaptation the later subcomponents (OP3 and OP4) showed a flattening of the slope of the latency-intensity function. The investigator concludes that this saturation effect is related to an interaction of rod and cone contribution to the OP waveform.     

Changes in Electroretinogram Oscillatory Potentials During Dark Adaptation

Purpose

To investigate changes in the oscillatory potentials (OPs) of electroretinograms (ERGs) during dark adaptation (DA).

Methods

ERGs were recorded from ten normal subjects. Following 15?min of light adaptation, ERGs were recorded every 30?s for 20?min to follow the changes in the OPs during the course of DA. A 20-ms, 560-nm rectangular pulse of light was presented at 3.3?Hz to elicit the ERGs.

Results

The latencies of OP1 and OP2 did not change significantly, but the amplitudes decreased slightly during DA. OP3 was not observed at 30?s, but appeared after 1?min of DA between OP2 and OP4. Similar results were obtained with stimulus durations of 10 to 100?ms in 10-ms steps. The amplitude of OP3 increased to 10?min of DA and then plateaued.

Conclusion

The characteristics of OP3, which increases during DA, indicate that it is probably related to rod activity. Jpn J Ophthalmol 2005;49:420–422 © Japanese Ophthalmological Society 2005     

Electroretinographic oscillatory potentials are reduced in adenylyl cyclase type I deficient mice

Electroretinography (ERG) of adult Adcy1(brl) mutant mice, which are deficient in adenylyl cyclase type 1 (AC1) activity, revealed decreased amplitude of the oscillatory potentials (OP) and of the primary rising phase of the b-wave intensity-response function in scotopic conditions. These abnormalities were less discernable in 3-6 week old mutants. No abnormalities were detected in the ERG signal obtained in photopic conditions or in the dark adaptation dynamics. The mutants displayed no histologic evidence of retinal degeneration. Retinal output, as measured by visual evoked potentials, was not different from heterozygous control mice. AC1-dependent pathways contribute to the generation of the retinal response to light. They may be necessary for the maintenance of the neural generators of the ERG OP.     

Neuronal adaptation in the human retina: a study of the single oscillatory response in dark adaptation and mesopic background illumination

PURPOSE: The single oscillatory response in complete dark adaptation (DA) and the effect of mesopic illumination were studied in order to investigate the behaviour of the neuronal adaptation system as reflected in the oscillatory potentials (OPs) of the electroretinogram (ERG). METHODS: The rapid oscillatory and slow components (a- and b-waves) of single ERGs were simultaneously recorded in nine healthy, young subjects in response to first flash after both DA of 45 mins and light adaptation to a steady background light (BGL) of low mesopic intensity. RESULTS: Two low-amplitude oscillatory peaks were present in the single response to the first flash recorded in DA. There was no increase in the summed amplitudes of the OPs (SOP) when recorded in the single response to the first flash in mesopic BGL. However, the morphology of the oscillatory response altered. The first OP was reduced and a third oscillatory peak appeared. CONCLUSIONS: We conclude that early, scotopically related OPs may indeed be activated in the single response to the first flash in DA (i.e. without using conditioning flashes). Secondly, on its own, adaptation to mesopic BGL does not seem to trigger enhancement of the overall oscillatory response. The altered single oscillatory response to the first flash apparent in the mesopic BGL comprises a third cone-associated OP and seems to reflect a reorganization of the retinal microcircuitry from a predominantly rod-activated system to one of mixed rod/cone neuronal activity in the inner part of the retina at the level at which individual OPs have their respective origins.     

Analysis of the photopic electroretinogram recorded before and after dark adaptation

To evaluate the effect of a long period of dark adaptation on the light-adapted electroretinogram (ERG), photopic ERGs were recorded before (light-adapted) and immediately after (light-readapted) 15 minutes of dark adaptation. The amplitude of the b-wave in the light-readapted ERG was 48% +/- 4% of that in the light-adapted ERG, and the peak time of the b-wave in the light-readapted ERG was delayed by an average of 3.49 +/- 1.09 ms. Segmental analysis of the b-wave showed that the last segment of the ascending limb of the b-wave (from the second oscillatory potential [OP] to the peak) was attenuated the most (61% +/- 8%). In fact, the reduction in the amplitude of the last segment alone accounted for more than 60% +/- 13% of the overall reduction observed for the entire b-wave. This last segment appears to correspond to OP4 in the 100- to 1000-Hz recordings. The amplitude of OP4 in the light-readapted ERG was 56.5% +/- 10% of that in the light-adapted ERG, a similar reduction to that observed for the last segment of the 1- to 1000-Hz b-wave. The results strongly support the concept that the b-wave of the photopic ERG may actually represent a composite of potentials whose individual contributions are best visualized when the ERG is recorded with the 100- to 1000-Hz bandwidth.     

Evidence for an intensity-coding oscillatory potential in the human electroretinogram

Electroretinograms (ERGs) were obtained from normal subjects to various combinations of stimulus and background intensities to examine if, as shown in rabbits, one of the oscillatory potentials (OP2) could be identified as reflecting the absolute intensity of the stimulus (i.e. the intensity irrespective of the state of retinal adaptation). The results presented clearly demonstrate that the peak time and the amplitude of OP2 are highly correlated with the absolute intensity of the stimulus. Linear regression analysis (for light- and dark-adapted data combined) yields a correlation coefficient of r = 0.98 for the peak time of OP2 and r = 0.88 for the amplitude of OP2. The latter equations were obtained from ERGs where the brightest flashes were delivered in light-adaptation and the dimmest in dark-adaptation. This is the first demonstration of a high correlation between the intensity of the stimulus and the amplitude and peak time of a human ERG component which is shown to be linear irrespective of the state of retinal adaptation.     

Dark and light adaptation of pineal photoreceptors

Dark and light adaptation of pineal photoreceptors was studied in the isolated pineal organ of the rainbow trout, Salmo gairdneri. After intracellular recording, the photoreceptors were iontophoretically injected with Lucifer yellow CH or with horseradish peroxidase for morphological characterization. Pineal photoreceptor cells responded to light with a hyperpolarization whose amplitude was graded with intensity. Following a 30-60 s bleach, receptor responsiveness was greatly reduced with a gradual recovery in the dark. Recovery of membrane potential was complete within 2-4 min in the dark. In response to flashes the hyperpolarizing response increased in darkness in amplitude and duration over a period of more than 30 min and the voltage-intensity curves continuously shifted to lower intensities. After exposure to strong light the time-course of dark adaptation, determined with a threshold criterion, was monophasic and receptor sensitivity increased by at least 5-6 log units. The results show that pineal photoreceptors exhibited the full characteristics of dark adaptation processes previously ascribed to cells proximal to the receptors, i.e. to ganglion cells. Exposure to steady illumination of different intensities induced graded and sustained hyperpolarizations of the receptor membrane potential. The incremental voltage range of responses to test flashes superimposed on the backgrounds was reduced. Voltage-intensity curves were shifted to higher intensities with increasing background illumination indicating that adaptation occurred over a range of about 2.5 log units before the receptors saturated.     

The effect of a slow flicker on the human photopic oscillatory potentials.

Flicker-induced modifications of the human photopic oscillatory potentials (OPs) were investigated with the use of flash stimuli of 0.89 and 8.9 cd m-2 sec in strength. When the dimmest stimulus is used, increasing the rate of presentation from 0.5 to 20 Hz augments the amplitude and peak time of OP2. For a brighter stimulus, the 10 Hz flicker significantly reduces the amplitude of OP2 and OP3, increases the peak time of OP2 and reduces that of OP4. The 20 Hz flicker increases the peak time and reduces the amplitude of OP2 and completely abolishes OP3, while it has no significant impact on the amplitude and timing of OP4. The data presented support the claim that each OP making the photopic response represent independent electrophysiological entities.     

The effect of post prandial glucose changes on oscillatory potentials in subjects with type 2 diabetes mellitus

Purpose: To investigate the effect of elevated plasma glucose levels on oscillatory potentials (OPs) in patients with diabetes mellitus. Method: 15 patients with type 2 diabetes mellitus, with no ophthalmoscopically visible signs of diabetic retinopathy (NDR), were recruited, mean (SD) age 65.1 (10.91) years and duration 5.95 (4.95) years. Plasma glucose levels and OPs were recorded before, during and after a meal tolerance test (MTT), at times 0, 90 and 210 min. OPs were recorded following 5 min adaptation to a blue mesopic background (1.17 cd m^–2), and elicited using a white 5 ms stimulus flickering at 5 Hz frequency over the blue background. Results: Plasma glucose increased significantly from 0 to 90 min during the MTT. This corresponded with an increase in mean amplitude of OP1–4, and a significant increase in the summed amplitudes. Summed OP amplitudes were 14.52 v and 18.38 v at time 0 and 90 min respectively. Between times 90 and 210 min plasma glucose levels decreased significantly back to baseline. OP1 and OP2 amplitudes increased slightly and OP3 and OP4 amplitudes decreased markedly, resulting in a non-significant reduction of the summed amplitudes. No significant changes in latencies were seen. Conclusions: Summed OP amplitudes, which are known to reflect the efficiency of the retinal circulation, increased with elevated plasma glucose. This effect was not immediately reversible. Latencies appear not to be affected.     

Relationships between the electroretinogram a-wave,b-wave and oscillatory potentials and their application to clinical diagnosis

The electroretinogram is the electrical response of the retina to a light stimulus. The amplitude and temporal pattern of its components, the a-wave, the b-wave and the oscillatory potentials, depend on the functional integrity of the retina, on the intensity of test flash reaching the retina and on the ambient illumination. The latter contributions to the normal variability in the electroretinogram can be circumvented by constructing the relationships between the different electroretinogram waves. The electroretinogram responses were recorded from 18 dark-adapted subjects with normal vision. The slope of the a-wave and the amplitude of the b-waves were measured in the time domain. The oscillatory potentials were isolated by a digital filter and were transformed to the frequency domain for quantitative measurement. The relationship between each pair of variables could be fitted by linear segments. Our findings suggest that this mode of electroretinogram analysis can be useful in localizing the site of action of retinal disorders and that the relationship between the a-wave slope and the power density of the oscillatory potentials is a useful index for identifying disorders of the inner retina.     

背景光照明强度对视网膜电图和振荡电位的影响

目的观察不同强度背景光照明下视网膜电图(electroretinogram, ERG) 和振荡电位(oscillatory potentials, OPs)的变化,了解视网膜神经性调控机制对环境照明改变的反应。方法应用自行设计的全视野刺激的ERG记录仪,采用 DTL纤维电极于角膜端记录出生25~29 d Albino鼠(Wistar Fu)眼在暗视及以2个对数单位递增的4个背景光强 度 ——“弱”(1.43×10^-6cd/m²)、“次弱”(1.43×10^-4cd/m²)、“ 次强”(1.43×10^-2cd/m²)和“强”(1.43×10^-2cd/m²)下的ERG a波和b 波。采用数字式滤波器,同时记录OPs。刺激闪光强度为1.43×10^-2cd/m²,闪光时程75 ms,闪光间隔时间1 min 。结果随着背景照明强度的增强,OPs子波数由5个减少至3个,但子波振幅总和增加。当背景光强度增强到最强水平,OPs振幅总和减少。ERG a波和b波振幅在2个弱背景光照明下未见改变。但在强背景照明范围,a波和b波振幅随照明强度的增强而呈下降趋势。结论Albino鼠视网膜内层存在的神经调控系统对环境照明改变的反应比感光细胞更敏感、更快。记录OPs时采用适当的连续背景光照明,可提高反应记录的稳定性。(中华眼底病杂志,2001,17:286-288)     

Clinical and electrophysiological findings in three patients with toluene dependency

We recorded the electrophysiological findings of three patients with toluene dependency who developed visual disturbance. In five of six eyes the peak latency of the pattern visual evoked cortical potential was prolonged as compared with that of normal subjects. The amplitude and the latency of the a-wave of the electroretinogram were decreased in five of the six eyes and prolonged in four. Those of the b-wave in patients were less affected than the a-wave: in one of six eyes the amplitude of the b-wave was decreased and in two the b-wave latency was prolonged. The amplitudes of the oscillatory potentials were decreased in three of six eyes. The electroretinogram was investigated in one patient and showed little increase in amplitude during light stimulation, so that a lowered light peak to dark trough ratio was obtained.Our findings suggest that any part of the visual pathway, including the distal part of the retina and retinal pigment epithelium, might be impaired by the chronic inhalation of toluene vapors.Abbreviations EOG Electrooculogram - ERG Electroretinogram - L/D light peak to dark trough ratio - OP Oscillatory potential - VECP Visual evoked cortical potential     

Origin of electroretinogram amplitude growth during light adaptation in pigmented rats

We assessed the growth of the rat photopic electroretinogram (ERG) during light adaptation and the mechanisms underlying this process. Full field ERG responses were recorded from anesthetized adult Brown-Norway rats at each minute for 20 min of light adaptation (backgrounds: 1.8, 2.1, 2.4 log scotopic cd m(-2)). The rat photopic b-wave amplitude increased with duration of light adaptation and its width at 33% maximal amplitude narrowed (by approximately 40 ms). These effects peaked 12-15 min after background onset. The narrowing of the b-wave reflected steepening of the b-wave recovery phase, with little change in the rising phase. OP amplitudes grew in proportion to the b-wave. Inhibition of inner retinal responses using TTX resulted in a greater relative growth of b-wave and OP amplitude compared with fellow control eyes, and delayed the change in recovery phase by approximately 5 min. Inhibition of all ionotropic glutamate receptors with CNQX/D-AP7 delayed both rising and recovery phases equally (approximately 12 ms) without altering b-wave width or the time course of adaptation changes. These outcomes suggest that inner retinal light responses are not directly responsible for b-wave amplitude growth, but may contribute to the change in its recovery phase during adaptation. A TTX-sensitive mechanism may help to hasten this process. The cone a-wave was isolated using PDA/L-AP4 or CNQX/L-AP4. A-wave amplitude (35 ms after stimulus onset) also increased with time during light adaptation and reached a maximum (130 +/- 29% above baseline) 12-15 min after background onset. B-wave amplitude growth in fellow control eyes closely followed the course and relative magnitude of cone a-wave amplitude growth. Hence, the increase of the cone response during light adaptation is sufficient to explain b-wave amplitude growth.     

Frequency spectrum and amplitude analysis of dark- and light-adapted oscillatory potentials in albino mouse,rat and rabbit

We studied frequency spectrum, implicit time and amplitude of oscillatory potentials (OPs) in albino mice, rats, and rabbits. Oscillatory potentials were extracted digitally from dark- and light-adapted electroretinograms (ERGs) recorded with a protocol commonly used in our laboratory. The frequency spectra of OPs were analyzed by using Fast Fourier Transform (FFT). Oscillatory potential amplitudes were calculated via numerically integrating the power spectrum. Oscillatory potential frequency spectra vary among species and are light-intensity dependent. In dark-adapted ERG, mouse and rat OPs have one major component with a frequency peak at approximately 100 Hz. Rabbits show multiple frequency peaks with a low frequency peak around 75 Hz. In all the three species, the implicit time of light-adapted OP is longer than that of the dark-adapted OPs. At a given intensity, mice have the highest OP responses. Our data suggest that the commonly used bandpass of 75 Hz (or even 100 Hz) to 300 Hz for OP extraction is insufficient in these animals. In order to acquire the complete OP responses from the ERG signals, it is necessary to determine the OP frequency spectrum. In this study, the lower end cutoff frequency was set at 40 Hz in mice, 65 Hz in rats and rabbits.