Origin of the ERG omitted stimulus response: evidence from patients with congenital stationary night blindness

Abstract

Abstract Purpose Purpose: The omitted stimulus response (OSR) of the full‐field flicker ERG is an additional response component that follows stimulus termination. It has been attributed to a resonant oscillation in depolarizing (ON) bipolar cells. We evaluated this proposal by determining whether an OSR is present in the flicker ERG of patients with the complete type of congenital stationary night blindness (CSNB1) and presumed ON‐pathway dysfunction. Methods Methods: Subjects included two patients with ERG findings typical of CSNB1 and 11 normally sighted individuals. Molecular genetic analysis confirmed a mutation in the NYX gene (Trp273Ter) of patient 1 and in the GRM6 gene (Arg621Ter) of patient 2. Monocular ERGs were recorded in response to full‐field sinusoidal flicker trains, ranging from 6.33 to 100 Hz, presented against a rod saturating background. The amplitude and relative delay of additional ERG responses following the offset of the flicker trains were analyzed. Results Results: Across the frequency range of 39 to 63 Hz, the number of ERG responses exceeded the number of stimulus cycles for all control subjects. The delay between the additional response component and the last stimulus cycle was frequency dependent, consistent with an OSR. In the two patients with CSNB1, however, the number of ERG responses equaled the number of stimulus cycles at all frequencies. Conclusion Conclusion: The absence of an OSR in these two CSNB1 patients supports the hypothesis that ON bipolar cells play a key role in the generation of this response.