ON THE OSCILLATORY POTENTIALS OF THE HUMAN ELECTRORETINOGRAM IN LIGHT AND DARK ADAPTATION

Abstract

The oscillatory potentials of the human ERG were studied in response to a series of three short light flashes of high luminance, the first two flashes conditioning a varying light adaptation of the retina. The energy and dominant frequency of the oscillatory response were evaluated mathematically by a combined impulse response and Fourier analysis. Most prominent oscillations were elicited when the retina was light adapted by strong conditioning flashes and stimulated at intervals of 30 sec or 1 min. The maximal intensity of stimulus light (log Is = 0) was about 5 × 104 photopic candelas/m2. The scotopic b‐wave was evoked at threshold by a stimulus intensity of log Is = ‐ 6.0. A distinct photopic b‐wave was recorded at log Is = ‐ 4.0 and the a‐wave at log Is = ‐ 3.3. Traces of oscillatory potentials were found at log Is = ‐ 3.3 and log Is = ‐ 3.0 in different experiments, thus approximately at the same intensity as the a‐wave. There was a linear increase of the energy of the oscillatory potentials on augmentation of stimulus intensity over three log units. Peak latencies of oscillatory potentials showed a fairly uniform shortening (about 6 msec) on increasing stimulus intensity provided that the retinal light adaptation was kept constant, and the dominant frequency of the oscillatory response remained within 120–130 Hz. When the retinal adaptation to light was increased by stronger conditioning flashes, peak latencies for the first and second oscillatory peak diminished, those for the third and fourth peak showing no significant change. Then, the dominant frequency of the oscillations declined from about 155 Hz (in dark adaptation) to about 110 Hz (in light adaptation). It was found that the peak latencies of the oscillatory potentials are defined by the stimulus intensity, but the frequency of this response varies with the state of retinal neural adaptation caused by short flashes of light.