Wavelength-dependent rod-cone transition of the electroretinographic response

We have used signal-averaging and vector voltmeter techniques to measure the rod-cone response transition of the primate corneal electroretinogram (ERG). Lights of 580 nm or shorter wavelength, flickering sinusoidally at 5 Hz, produced nearly sinusoidal ERG's with a rod-type spectral sensitivity. For stimuli of 600 nm or longer wavelength, the ERG exhibited cone as well as rod response components; the ERG response became increasingly nonlinear and measurements of sensitivity and phase grew more variable. Our results show how phase information may reveal changes in response nonlinearities. Response shape and vector voltmeter phase readings are more accurate indicators of the boundary between rod-only vs. rod-cone mixed responses than are vector voltmeter magnitude readings. Shifts in the rod-cone response boundary could perhaps be exploited clinically to test for some anomalous visual processes.