The electrically evoked response (EER) of the visual system. II. Effect of adaptation and retinitis pigmentosa.

In an attempt to learn the stimulus site of the EER, the following series of experiments was performed. (1) The effect of dark adaptation on EER and VER was determined. The effect was found to be negligible. (2) The effect of eliciting the electric phosphene on the course of dark adaptation was determined. Under our conditions there was no effect. (3) The effect of ambient light on amplitude of EER and VER was determined. Moderate levels of ambient light 7.0 foot-lamberts abolished the VER but 2 x 10 foot-lamberts decreased the EER only 20 per cent in one subject, less in others. (4) The determination of VER and EER on retinitis pigmentosa patients gave varied results. In some patients neither response could be elicited. In several others a sizeable EER coidd be obtained with our standard stimulus. To obtain a VER of the same subjective brightness a light level ivas required that was higher than for normal subjects. Since in all these instances the variables affecting the VER were not the same as those affecting the EER, it is assumed that the cell of origin is not the same for the tioo phenomena. If the cell of origin of the VER is the photoreceptor, it is probable that the cell of origin of the EER is more central than the photoreceptor.