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Hendrik P. N. Scholl, Jan Kremers; Large Phase Differences between L-Cone– and M-Cone–Driven Electroretinograms in Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2000;41(10):3225-3233.
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purpose. To study the dynamics and interactions of the signals originating in
the long- (L-) and middle (M)-wavelength–sensitive cone pathways in
patients with retinitis pigmentosa (RP).
methods. Twenty-six patients with RP and 29 normal subjects participated in the
study. Electroretinographic (ERG) responses were measured to stimuli
that modulated exclusively the L- or the M-cones or the two
simultaneously (both in-phase and in counter-phase) with varying ratios
of L- to M-cone contrasts. S-cones were not modulated.
results. The data of the normal subjects and of the patients can be described by
a model in which the amplitudes and the phases of the signals
originating in the L- and M-cones are vector summed. In the RP
patients, there was a general reduction in ERG sensitivity. The
L-cone–driven ERG response was significantly delayed, whereas the
M-cone–driven ERG response was phase advanced.
conclusions. Large dynamic differences between L- and M-cone–driven ERGs can be
detected in RP. As a result, the interaction between the L- and M-cone
systems, when modulated simultaneously at 30 Hz, is subtractive in RP
patients and additive in normal subjects. Our data show that the use of
only a standard white flicker ERG might lead to a misinterpretation of
the mechanisms involved in retinal disorders, because the phases of
different cone-driven responses are not
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