RESPONSE PHASE OF THE FLICKER ELECTRORETINOGRAM (ERG) IS INFLUENCED BY CONE EXCITATION STRENGTH

We measured electroretinogram (ERG) response phases at different cone contrasts in trichromats and dichromats to investigate the dynamics of the long-wavelength-sensitive (L-) and middle-wavelength-sensitive (M -) cone pathways. ERG responses to stimuli, temporally modulated at 30 Hz, were recorded. The stimuli were generated on a computer controlle d colour monitor. Thirty-two different combinations of L- and M-cone e xcitation strength, expressed as cone contrasts, were presented. The s hort-wavelength-sensitive (S-) cones were not stimulated (S-cone contr ast = 0%). The response phase of the fundamental stimulus component wa s obtained from Fourier analysis. The ERG response phase lags decrease d with increasing cone contrast. This was observed in all subjects wit h a normal appearing fundus. In dichromats and trichromats at low and intermediate contrasts, the phase lags to M-cone isolating conditions were smaller than those to L-cone isolating stimuli. In one dichromat with extreme myopia and cupping of the optic disc, the ERG phase lags increased with increasing cone contrast. The ERG response phase may be potentially useful for detecting retinal abnormalities. (C) 1998 Else vier Science Ltd. All rights reserved.