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Ger J Ophthalmol. 1994 Nov;3(6):433-9.

Dual rod pathways in complete achromatopsia.

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Universitäts-Augenklinik Tübingen, Abteilung II, Germany.


The vision in typical complete achromatopsia is mediated only by rods. To provide more information about the physiological basis of this disorder, we investigated in a typical complete achromat the electrophysiological correlate of the psychophysically established 15-Hz-flicker nulling phenomenon. This phenomenon is believed to be the result of destructive interference between two independent rod pathways. We obtained dark-adapted Ganzfeld electroretinogram (ERG) recordings at 15 Hz with increasing stimulus intensities in the scotopic range and compared the results of the typical complete achromat with those of a normal observer. In both observers the 15-Hz ERG signal reached a minimum at retinal illuminances associated with the perceptual null and reversed in phase as the null was traversed. In comparison with the normal observer, however, the null in the achromat was found at higher scotopic retinal illuminances (ca. 0.4 log unit). Furthermore, the loss in amplitude associated with the null was much more evident, the decline in amplitude was steeper, and the phase shift of 180 degrees was accelerated.

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