A composite nature for the photopic b-wave of the human electroretinogram as evidenced by the use of the 60 Hz notch filter.

The impact of the 60 Hz notch (rejection) filter was examined in typical photopic electroretinograms recorded with two different bandwidths: 1-1000 Hz and 100-1000 Hz. The peak times of the major ERG components (a- and b-waves) are not modified by the line filter. The amplitude of the b-wave decreases by 30%, and the morphology of the ERG wave changes slightly. Segmental analysis of the ascending limb of the b-wave reveals that the sole reduction in the amplitude of its first step (from the a-wave trough to the peak of the first oscillatory potential) accounts for more than 70% of the overall reduction measured for the b-wave. Similar results are also found in ERGs recorded with the 100-1000 Hz bandwidth. The data suggests that the b-wave of the ERG should be considered as a composite of potentials rather than as a single potential.