The influence of stimulus duration on the human d.c. registered c-wave. A quantitative study

The c-wave of the human ERG was studied at different stimulus durations with a d.c. technique which permitted stable and reproducible recordings. With increasing stimulus lengths the implicit time increased up to a maximum of about 5.5 s. Also the amplitude of the c-wave rose. However, it was influenced by positive and negative off-effects, seen in most volunteers, and at several stimulus lengths superimposed upon the peak of the c-wave. This fact must be considered when developing a standardized method for measuring the c-wave amplitude proper.     

Effects of sodium iodate on the electroretinogram c-wave in the cat.

The c-wave of the vitreal electroretinogram decreased in amplitude and was replaced by a slow, polarity reversed potential following an i.v. infusion of sodium iodate, as first described by Noell. Intraretinal recordings showed that the negative-going c-wave, induced by iodate (30 mg/kg), was composed of reduced slow pIII and trans-epithelial c-wave. The effects of iodate on these components may originate from direct effects on the retinal pigment epithelial cells, namely, a large decrease in the trans-epithelial resistance. Other factors could have contributed to the change in the c-wave amplitude.     

The C-wave in hereditary degenerations of the ocular fundus

The c-wave of the human direct current ERG may give new insights about the involvement of the retinal pigment epithelium in hereditary degenerations. In our single-sweep recordings from 236 alert patients we saw reduced c-waves not only in vitelliforme macular degenerations but also in dominantly inherited drusen, Stargardt's disease, cone dystrophies, and x-linked retinoschisis. In achromatopsia the c-wave was close to normal.The relationship of the b- and c-wave, however, was altered only in Best's disease, cone dystrophy, and x-linked retinoschisis.We postulate that the c-wave when more severely reduced than the b-wave reflects not merely the dysfunction of the pigment epithelium but more precisely whether this retinal layer is involved earlier than the photoreceptors.Supported by the Deutsche Forschungsgemeinschaft SFB 70.     

Some characteristics of the c-wave of ERGs recorded by a pair of electrodes on the cornea and sclera

Summary Light-evoked responses of the rabbit retina in situ were recorded between the electrode on the longitudinal line of the nasal side (positive) and the electrode on the opposite longitudinal line of the temporal side (negative). The c-wave was negative and the a-, b-wave was reversed when the negative (temporal) electrode was closer to the corneal center than the positive (nasal) electrode. The c-wave decreased its amplitude as the positive electrode came to the same latitudinal position as that of the negative one. Then, the c-wave was cancelled out in appearance on the recordings. When the negative electrode moved further into the posterior pole, the polarities of the c-wave as well as of the a-, b-wave were returned to those of routine ERGs.     

Corneal D.C. recordings of slow ocular potential changes such as the ERG c-wave and the light peak in clinical work

A set-up for D.C. recordings of slow ocular potentials such as the c-wave of the electroretinogram (ERG) as well as the fast oscillation (FO), the light peak (LP) and the dark trough (DT) in both clinical and experimental work is described. It includes matched calomel half-cells connected by saline-agar bridges to a corneal contact lens on the eye and a reference chamber on the forehead, a low-drift differential-input D.C. amplifier, an A/D converter, a computer, a thermoprinter, a flexible disc memory, a plotter, and a device for light stimulation controlled by the computer.Examples of the usefulness of the set-up in clinical work are shown in the form of D.C. c-wave ERGs of normal subjects as well as of patients with vitelliform macular degeneration, choriocapillaris atrophy, and retinitis pigmentosa. The direct corneal recording of the FO and LP is demonstrated as well. The different origins of the standing potential (SP) of the eye, the ERG c-wave, the FO and the LP are reviewed briefly.     

Covariation of the simultaneously recorded c-wave and standing potential of the human eye.

The c-wave and the directly recorded standing potential (SP) of the human eye were studied with the aid of a recently developed method including matched temperature stabilized calomel electrodes, d.c. amplifiers and a suction contact lens. This technique, which does not require general anaesthesia, permits simultaneous direct d.c. recordings of the SP and the c-wave in human volunteers during long-term experiments. Upon repetitive light flashes (stimulus duration 1 sec, interval 20 sec and flash intensity 4.5 rel. log units above b-wave threshold) both variables responded with slow amplitude oscillations with a frequency of about 2/hour. The oscillations were similar as to phases and frequencies. Both the potentials are held to be generated mainly in the pigment epithelium. Considering this partly common origin the observed covariation was an interesting finding.     

Progressive retinal atrophy in the Abyssinian cat: studies of the DC-recorded electroretinogram and the standing potential of the eye.

DC-recorded electroretinography (ERG) and direct recordings of the standing potential (SP) were performed on a group of normal cats and Abyssinian cats affected by a hereditary retinal degenerative disease with similarities to human retinitis pigmentosa. A significant reduction of a- and b-wave amplitudes was found at an early stage of disease at a time when there were no major alterations in the c-wave and SP. At later stages both the c-wave and the SP oscillations were significantly reduced or absent. These findings indicate a primary photo-receptor disorder. Threshold studies for the scotopic b-wave showed a loss of retinal sensitivity early in the disease at a time when 30 Hz flicker responses were normal, which could indicate an earlier involvement of the rods than of the cones. There were no major alterations in the timing of the ERG in the affected animals tested.     

Light-emitting diodes and half-cell electrodes in experimental recording of electroretinogram c-wave

A method of electroretinogram c-wave recording in the rat was developed that uses a contact lens electrode connected through a saline bridge with a silver-silver chloride half-cell. A cluster of light-emitting diodes, regulated by an electronic light-emitting diode stimulator, was used as a light source. The method enables recordings of c-waves of 0.4–1.6 mV amplitude as well as other electroretinogram components in narrow limits of variation. The two main sources of response variability are voltage shunting and eyeball protrusion.     

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

In 10 experiments on five albino rabbits, the direct-current electroretinogram and the standing potential of the eye were recorded in response to repeated light stimuli (duration, 10 s; interval, 70 s), presented in four series, each consisting of 25 light flashes. Light intensities were, in order of presentation to the eyes, 3, 2, 1 and 0 log rel units (series I, II, III and IV, respectively) below the maximum output of the system. Thirty minutes of dark adaptation preceded each series. At the end of series I, the mean amplitudes of the b- and c-waves were higher and that of the a-wave relatively unchanged compared with the corresponding initial amplitudes. During series II–IV, there was a marked decrease in mean a- and b-wave amplitudes between the first and the following electroretinogram responses, and at the end of the three series, the amplitudes were still significantly reduced compared with the corresponding initial values. The mean c-wave amplitude was also markedly decreased immediately after the first electroretinogram recording, but it later recovered to a large extent. A peak in the c-wave amplitude was discerned about 14–18 minutes after the start of the recordings. A standing potential minimum during the second light stimulus was followed by a peak after about 10–13 minutes. The partially parallel behavior of the c-wave and the standing potential suggests the operation of a pigment epithelial mechanism behind the recovery of the c-wave amplitude. The final amplitudes of the b- and c-waves, and to a large extent also of the a-wave, were about the same irrespective of stimulus intensity. The adaptational processes in the rabbit appear to be more complicated than was previously thought. 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.     

Mechanisms of azide induced increases in the c-wave and standing potential of the intact cat eye

The c-wave of the ERG and the standing potential of the eye both undergo increases in amplitude following intravenous infusions of sodium azide (NaN3), as first shown by Noell [Am. J. Physiol. 170, 217-238 (1952); U.S.A.F. School of Aviation Medicine, Project No. 21-1201-0004 (1953)]. We have studied the mechanism of these changes in the intact cat eye. Intraretinal and intracellular retinal pigment epithelial (RPE) cell recordings show that most of the change occurs at the RPE, but that there is a small direct effect on the neural retina. The increase of standing potential is caused by a depolarization of the basal membrane of the RPE, and the increase in c-wave amplitude results from a decrease in basal membrane resistance that accompanies the depolarization. This relation between basal membrane potential and resistance is similar to that observed during hypoxia and during the light peak of the d.c. ERG.