Comparison of photopic and scotopic characteristics in human ERG B-Waves and off-responses
Electroretinograms (ERGs) recorded from animals with all rod or all cone retinae show negative or positive off-responses, respectively. In the present study, data have been obtained which demonstrate that the mixed retina of man produces both these types of off-responses under appropriate stimulus conditions. The stimulus light was a 150 watt xenon source. Recordings were obtained using four different stimulus wavelengths at three intensities for times varying between 0.25 to 16 seconds. The source was balanced to match the scotopic standard observer. ERG potentials were detected by a specially constructed contact lens electrode which, when illuminated, produced a Gonsfeld stimulus to the subject. All recordings were d.c. coupled and stored for averaging in a signal averager. The data for this study have shown that negative off-responses are associated with the scotopic retinal mechanism while positive off-responses are associated with the photopic retinal mechanism. Further, the type of off-response associated with a wavelength was found not to be altered by increased stimulus duration. The positive off-response was found to be more complex than would be predicted by the classical component analyses of the ERG. This complexity has been shown to be purely photopic in nature.