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A large literature has developed on the electroretinogram (e.r.g.); for the most recent review see Crescitelli (1960). Structures generating the various components, however, are still not clearly identified. This problem must be solved before the significance of the e.r.g. in the visual process can be understood and before the e.r.g. can be accurately interpreted as a tool for visual research or clinical diagnosis.A number of investigators have now attacked this problem by using micropipette electrodes to record the intraretinal potentials of the frog retina

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It has been hypothesized that the light-evoked rod hyperpolarization (the receptor potential) initiates the light-evoked decrease in extracellular potassium ion concentration, [K+]o, in the distal retina. The hypothesis was tested using the isolated, superfused retina of the toad, Bufo marinus; the receptor potential was recorded intraceilularly from red rods, and [K+]o was measured in the photoreceptor layer with K+-specific microelectrodes. In support of the hypothesis, variations in stimulus irradiance or duration, or in retinal temperature, produced qualitatively similar effects on both the receptor potential and the decrease in [K+]o. A mechanism for the relationship between the receptor potential and the decrease in [K+]o was suggested by Matsuura et al. (1978. Vision . In the dark, the passive efflux of K + out of the rod is balanced by an equal influx of K + from the Na+/K + pump. The light-evoked rod hyperpolarization is assumed to reduce the passive efflux, with little effect on the pump. Thus, the influx will exceed the efflux, and [K+]o will decrease. Consistent with this mechanism, the largest and most rapid decrease in [K+]o was measured adjacent to the rod inner segments, where the Na+/K + pump is most likely located; in addition, inhibition of the pump with ouabain abolished the decrease in [K+]o more rapidly than the rod hyperpolarization. Based upon this mechanism, Matsuura et al. (1978) developed a mathematical model: over a wide range of stimulus irradiance, this model successfully predicts the timecourse of the decrease in [K+]o, given only the time-course of the rod hyperpolarization.