In this study, we compared the photoreceptor and the ON- and OFF-contributions with the brief-pulse 32-Hz flicker ERG fundamental component and with the sine-wave
9 and square-wave flickers. Because stroboscopic flashes are widely used in the clinic, vector-modeling analysis may be useful for interpreting the changes resulting from retinal disease. For instance, Kim et al.
8 analyzed the fundamental component of 30-Hz strobe flicker ERGs in patients with complete congenital stationary night blindness (cCSNB), who are thought to have a defect in signal transmission from photoreceptors to the postreceptoral ON-pathway.
5 21 22 cCSNB showed a delay of the fundamental phase without a significant amplitude reduction. Similarly, these monkey studies showed that removal of the ON component by APB caused a substantial phase delay without any notable amplitude reduction for stroboscopic stimulation
(Fig. 6) . This suggests that vector analysis may be useful for interpreting flicker ERG changes in presumed postsynaptic retinal diseases. One difference between the patients with cCSNB and the monkeys studied was that the delay in the monkey responses after APB was two times larger (58°) than in the patients with cCSNB (28°).
8 This difference may be partly due to differences between species. Alternatively, it suggests that the pathologic course of cCSNB may be more complex than the relatively pure pharmacologic blockage of the ON component by APB. Recent genetic analysis of X-linked cCSNB identified mutations in
NYX gene that encode the nyctalopin protein, and suggested that mutant nyctalopin may impair proper development of the ON pathway circuit.
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