A portable ERG system with a Ganzfeld stimulation and adaptation light source is described. The stimulus flash energy can be selected from a range of 3.9 log units and the adapting background can be 0,10 or 100 lux at the cornea. The whole system has the dimensions of a standard ECG recorder, can operate independently of the main voltage and can be used in electrically unshielded rooms. It has a programmed measuring cycle that controls the paper transport, the changeover of the registration channel from one eye to the other, the stimulus presentation and the registration of a standard calibration pulse (100 µV/100 ms).

A Ganzfeld light source, fitted on an electroretinogram contact lens, is described. The light source can provide blue, green, or red flashes with intensities over a range of 3.6 log units. It can also be used to provide a continuous light-adapting background in each of the above-mentioned colors, simultaneously presenting the possibility of emitting flashes. The control unit and the light source can be powered by a small battery pack.

A tri-color Ganzfeld stimulator with light-emitting diodes as light sources is used to study the suppression of the second electroretinographic response in human eyes to double-flash stimulation. The mechanism suppressing the a- and b-waves of the response to the second (test) flash has a scotopic spectral sensitivity to the first (conditioning) flash. Responses to mild test stimuli are more sensitive to suppression by a conditioning flash than responses to strong test stimuli.

Neural adaptation to light stimulation in the dark-adapted retina can be demonstrated by double-flash electroretinography. The first flash is a conditioning flash, the second flash is the test flash. Interstimulus intervals are in the range of 0.2 to 30 seconds. Suppression of the response to the test flash is assumed not to be related to photopigment regeneration, as in normal human subjects the recovery after strong conditioning flashes is completed in about 2 seconds. In this paper we demonstrate the results of double-flash electroretinography on four patients, two of whom are brother and sister. Each of them showed a five- to ten-fold prolonged suppression time compared to normal measurements. Clinical aspects of all the patients were a stationary, though fluctuating, subnormal visual acuity of about 0.5, some photophobia, and difficulties in adaptation to changes in luminance levels. We assume that the PERRS indicates changes in the restorative reactions to phototransduction in the photoreceptors, or in the neural transmission mechanism, either in the rod-driven lateral inhibitory neural processes or in the cone-driven rod inhibitory processes, caused by a cone dysfunction.