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Large Phase Differences between L-Cone– and M-Cone–Driven Electroretinograms in Retinitis Pigmentosa

From the Department of Experimental Ophthalmology, University Eye Hospital, Tübingen, Germany.

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 considered.

This article has been cited by other articles:

				H. P. N. Scholl, J. Kremers, R. Vonthein, K. White, and B. H. F. Weber L- and M-Cone-Driven Electroretinograms in Stargardt's Macular Dystrophy-Fundus Flavimaculatus Invest. Ophthalmol. Vis. Sci., May 1, 2001; 42(6): 1380 - 1389. [Abstract] [Full Text]