THE EARLY RECEPTOR POTENTIAL IN THE HUMAN ELECTRORETIN OGRAM

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Abstract
A new rapid potential with a very short latency was reported in the human electroretinogram (ERG). This new potential was tentatively called the early potential (EP). Evidence showed that the EP in man is essentially identical with the early receptor potential (ERP) in other vertebrates. Intense photic stimulation with a very short rise time was needed to evoke the ERP in man. The EP obtained from normal subjects was seemingly biphasic in form, consisting of a small cornea-positive phase followed by a dominant cornea-negative one. The latency of the cornea-positive phase was less than 30 [mu]sec. The latency of the a-wave elicited with the intense stimulus was as short as 1.7 msec, being the shortest value thus far reported for the a-wave of the human ERG. This may support the view that an origin of the a-wave of the human ERG lies in the visual cells. The amplitude of the cornea-negative phase of the EP in man was approximately linearly related to the stimulus intensity for the first 1.1 log units above the threshold. In this range of stimulus intensity, the a- and b-waves showed no significant increase in amplitude. The EP in man was not so greatly affected by moderate light adaptation as the ordinary ERG components. This implies that at suitable levels of light adaptation the EP can be practically isolated from the ordinary ERG components. The EP comparable in size and time course to the normal control was observed in long-standing simple atrophy of the optic nerve and complete obstruction of the central artery of the retina. The EP was entirely abolished in idiopathic total detachment of the retina as well as even in early stages of the primary pigmentary degeneration of the retina. These findings may indicate that the EP in man is closely related to the activity of the visual cells. A new cornea-positive potential, the summit of which appeared between the cornea-negative phase of the EP and the a-wave, was detected in cats, albino rats, pigeons and tortoises. This finding, coupled with the arguments in this paper, may advance a working hypothesis that the EP shows an additional cornea-positive phase in some conditions.