Selective Adaptation of L- and M- sensitive Cones Assessed by the Receptor Specific Flicker ERG and Psychophysically

¹Stepien M. W., ²Kremers J., ³Scholl H. P. N., ⁴Gos R.,
¹Eberhard-Karls-Universität, Augenklinik (Lodz)
²Eberhard-Karls-Universität Tübingen, Universitäts-Augenklinik, Abt. II (Tübingen)
³Institute of Ophthalmology, Moorfields Eye Hospital (Tübingen)
⁴Military Medical University of Lodz, Department of Ophthalmology (Lodz)

Purpose: To asses the effects of selective L- and M-cone adaptation on the cone driven responses in the ERG and in the psychophysical flicker detection sensitivity (FDS) in dichromats and trichromats.
Method: Normal trichromats and single-gene dichromats (protanope and deuteranopes) participated in the study. ERG responses were obtained with 30 Hz stimuli, that stimulated selectively L- or M-cones with 15% cone contrast. FDS to L- and M-cone isolating stimuli at different temporal frequencies (TF) were measured. The measurements were performed at a reference state of adaptation and at 4 additional states, in which either the L- or the M-cones were selectively adapted.
Results: At the reference conditions and after an adaptation to a greenish light, all trichromats have larger ERG responses and FDSs at high TF to L- than to M-cone modulation. After a change to a reddish light the M-cone ERG responses and FDSs at high TF were larger. L- and M-cone FDS at low TF were equal at all adaptations. At all states of adaptation the protanopes showed ERGs and FDSs to M- but not L-cone modulation. The deuteranopes showed no ERG responses and FDSs to M-cone modulation at the reference condition and when adapted to a greenish light. When adapted to a reddish light, ERGs and FDSs to L-cone modulation were reduced and substantial M-cone responses could be measured. Repeating the FDS measurements at higher retinal illuminances and with pure foveal stimulation gave similar results.
Conclusions: The results of the measurements with the protanopes and the differences in results between high and low TF for the trichromats exclude the possibility of a stimulus artifacts. Cone selective ERGs and FDSs at high TF (mediated by the luminance channel) can be influenced by adaptation. The chromatic channel, mediating FDSs to low TF, is not influenced by adaptation. The measurements in the deuteranopes indicate that another green absorbing pigment may influence the data.

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