The c-wave of the direct-current-recorded electroretinogram and the standing potential of the albino rabbit eye in response to repeated series of light stimuli of different intensities

The determination of dark adaptation time using electroretinography in conscious miniature Schnauzer dogs

The optimal dark adaptation time of electroretinograms (ERG's) performed on conscious dogs were determined using a commercially available ERG unit with a contact lens electrode and a built-in light source (LED-electrode). The ERG recordings were performed on nine healthy Miniature Schnauzer dogs. The bilateral ERG's at seven different dark adaptation times at an intensity of 2.5 cd·s/m² was performed. Signal averaging (4 flashes of light stimuli) was adopted to reduce electrophysiologic noise. As the dark adaptation time increased, a significant increase in the mean a-wave amplitudes was observed in comparison to base-line levels up to 10 min (p < 0.05). Thereafter, no significant differences in amplitude occured over the dark adaptation time. Moreover, at this time the mean amplitude was 60.30 ± 18.47 µV. However, no significant changes were observed for the implicit times of the a-wave. The implicit times and amplitude of the b-wave increased significantly up to 20 min of dark adaptation (p < 0.05). Beyond this time, the mean b-wave amplitudes was 132.92 ± 17.79 µV. The results of the present study demonstrate that, the optimal dark adaptation time when performing ERG's, should be at least 20 min in conscious Miniature Schnauzer dogs.

Concentration-dependent effects of dopamine on the direct current electroretinogram of pigmented rabbits during prolonged intermittent recording

The direct-current (DC) electroretinogram (ERG) was studied in 24 pigmented rabbits. Four experiments were performed, each including six animals. One eye was injected intravitreally with 0.1 ml dopamine (DA) with an estimated concentration in the vitreous body of 0.0025 mM, 0.025 mM, 0.25 mM and 2.5 mM, respectively. The contralateral eye was injected with the same amount of saline. Following the injection the animals were dark adapted for 30 min and then exposed to repeated light stimuli of low intensity for almost 3 hours (series I: 1 stimulus per 3 min, 10 s duration, light intensity 6.8 x 10(2) lux). After another 30 min period of dark adaptation repeated light stimuli of high intensity were presented to the eyes (series II: 1 stimulus per 70 s, 10 s duration, light intensity 6.8 x 10(4) lux) for 33 min. In the control eyes, a slow increase with time of the a-, b- and c-wave amplitudes was observed during series I. During series II, the a- b- and c-wave amplitudes were markedly reduced between the first and the second light stimulus, but subsequently grew to a peak. The behavior of the ERG in the eyes injected with dopamine was not different from that observed in the control eyes at the lowest concentration of the drug. At higher concentrations the b- and c-wave amplitudes were reduced compared with the control eyes, and did not show the slow increase with time observed in these eyes during series I. Peak responses observed during series II in the control eyes was increasingly suppressed in the eyes treated with dopamine. Results of ERG recordings suggest that dopamine influences retinal adaptation in rabbits in a dose dependent manner.

Long-term behavior and intra-individual stability of the direct current electroretinogram and of the standing potential in the albino rabbit eye

The direct current electroretinogram (ERG) and the standing potential (SP) were studied in seven albino rabbits under general anesthesia. Identical experiments were performed on 2 consecutive days. After 30 min of dark adaptation, repeated light stimuli of maximal intensity of the system were presented to the eyes. The interstimulus interval was 70 s, and stimulus duration 10 s. Each experiment lasted for almost 3 h. In the first experiment, the b- and c-wave amplitudes measured in response to the second light stimulus were markedly reduced compared to those recorded in response to the first stimulus. Both amplitudes then recovered. The b-wave attained a peak about 20 min after the start of light stimulation. The peak was followed by a trough about 20 min later, and the amplitude then slowly increased. Following the minimum recorded during the second light stimulus, the c-wave amplitude reached a peak about 14 min after the start of stimulation. A trough in the amplitude occurred 20 min later. The amplitude then slowly increased to the end value, which was higher than the initial level. The a-wave behaved similarly to the b-wave, but the changes in most cases did not attain statistical significance. A minimum in the SP occurring at the second light stimulus was followed by a peak about 13 min after the start of light stimulation, and then by a trough about 17 min later. In the second experiment, performed one day after the first, the development of the a-, b-, and c-wave amplitudes and of the SP was similar to that observed during the first experiment, and no statistically significant differences between the two experiments were found. The reactions of the ERG and the SP were thus very stable between identical experiments performed on two consecutive days.

Changes in the Direct-Current Electroretinogram of Albino Rabbits during Prolonged Intermittent Recording

The study investigated the pattern of the direct-current electroretinogram (ERG) of albino rabbits during prolonged intermittent recording, and whether different initial dark adaptation periods or starting the experiments at different times influenced the results. We examined 27 rabbits under general anesthesia, in three experiments, each comprising nine animals. Five series (experiments 1 and 3) or four series (experiment 2) of ten repeated light stimuli were presented to the eyes with 30 minutes of dark adaptation before experiments 1 and 3, and 90 minutes before experiment 2. The dark adaptation of experiments 1 and 2 began at 10.30 a.m. and that of experiment 3 at 3.30 p.m. The interval between consecutive series of light stimuli was 33 minutes. Stimulus intensity was 680 lux, stimulus duration 10 seconds, and the interval between stimuli 3 minutes. The mean b-wave amplitude of the ten recordings in each series of stimuli increased up to the series beginning 3.5 hours (experiments 1 and 2) or 2.5 hours (experiment 3) after the start of dark adaptation. The mean c-wave amplitude increased throughout experiments 1 and 3, and up to the series beginning 3.5 hours after the start of dark adaptation in experiment 2. The mean a-wave amplitude was more stable. It seemed irrelevant for the long-term development of the mean ERG amplitudes whether the eye was dark adapted (experiment 2) or exposed to repeated light stimuli (experiments 1 and 3) during the first part of the experiment, and whether the experiments started in the morning or in the afternoon.

Effects of prolonged uniocular dark adaptation on the direct-current electroretinogram of pigmented and albino rabbits

The direct-current electroretinogram of seven pigmented and seven albino rabbits was recorded from both eyes for almost 4 h in response to repeated identical light stimuli. Stimulus duration was 10 s, light intensity was 6.8 x 10(2) lux, and the interval between the beginning of succeeding light stimuli was 3 min. The dark-adaptation period preceding light stimulation was 30 min for one of the eyes ('unoccluded eye') and 150 min for the contralateral eye ('occluded eye'), which was patched during the first part (117 min) of the experiment. In pigmented animals, the b- and c-wave amplitudes of the unoccluded eye slowly increased during the first part of the experiment but not significantly during the second. The a-wave amplitude was not significantly changed. After removal of the cover, the a- and b-wave amplitudes of the occluded eye immediately attained but not exceed the level of those in the unoccluded eye, irrespective of the light adaptation induced by the stimulus flashes previously presented to the unoccluded eye. (Control experiments on six pigmented rabbits confirmed that stimuli identical to those used in the main part of the study caused a light adaptation, since a decrease in a- and b-wave amplitudes occurred after the first light stimulus following an initial dark-adaptation period of 2 h for both eyes). In albino rabbits, electroretinogram responses were clearly discernible in the occluded eye also during the first part of the experiment, probably because of transillumination of the head. In other respects, the results were essentially similar to those of pigmented animals. The observation that occluded eyes did not dark adapt better, as judged by the electroretinogram responses, than contralateral eyes given repeated light adaptive stimuli may indicate the presence of a mechanism for transfer of adaptation information between the eyes.

The c-wave of the direct-current electroretinogram and the standing potential of the albino rabbit eye in response to repeated series of light stimuli with different interstimulus intervals

The direct-current electroretinogram and the standing potential of the eye of seven albino rabbits were recorded in response to repeated light stimuli, which were presented in four consecutive series. The intervals between the beginning of succeeding stimuli were 8 minutes, 4 minutes, 2 minutes and 70 seconds (series 1, 2, 3 and 4, respectively). Stimulus duration (10 seconds) and light intensity (6.8 x 10(4) lux) were constant during the experiments. The series lasted for 36-40 minutes, and each was preceded by 30 minutes of dark adaptation. During series 1, the end amplitudes of the a-, b- and c-waves were not significantly changed compared with the initial levels. During series 2, 3 and 4, the a-, b- and c-wave amplitudes were markedly reduced immediately after the first electroretinogram recording. The a- and b-waves then recovered to a limited extent, but the c-wave was more fully restored. A slight peak in the c-wave amplitude could be discerned 16-20 minutes after the start of recording. A decrease in the standing potential was seen 50-54 seconds after the start of light stimulation during all four series, and a peak occurred 12-16 minutes after the start of recording. The similarity in behavior between the c-wave and the standing potential suggests the operation of a pigment epithelial mechanism behind the more complete recovery of the c-wave amplitude. When electroretinogram amplitudes and standing potential levels are discussed, and when one experiment is compared with another one, it is important that adaptational and stimulus conditions, as well as time course, are well controlled and clearly specified.