Advance in ERG Analysis: From Peak Time and Amplitude to Frequency, Power, and Energy
Figure 1
Fourier analysis (FA) of 4 normal ERGs. The frequency spectrums are shown as normalized power spectrum, in percentage, where the spectrums are normalized to their maximal value. The associated ERGs are shown at the bottom of each spectrum. The a-wave, b-wave, and OPs are indicated as “a,” “b,” and “OPs,” respectively. (a) FA of a composite ERG, averaged from 40 subjects, showing the 3 typical frequency components that contribute to the ERG (~30 Hz: a- and b-waves contribution, black arrow; ~75 Hz and ~150 Hz: oscillatory potentials (OPs) contribution, gray arrows). (b) FA of an ERG showing enhanced OPs (increased ~75 Hz and ~150 Hz component contribution; thick gray arrows). (c) FA of a typical contaminated ERG showing the 3 standard ERG components (see arrows, same color-coding as previous panels) and a sharp, noise-related, maximal component at 60 Hz (60-cycle line interference contribution, red arrow). This sharp noise component seems to disturb the identification of the OPs component located at ~75 Hz. (d) FA of another contaminated ERG showing the 3 characteristic frequency components (see arrows, same color-coding as previous panels) of the ERG and 4 interference-related components at 60, 120, 180, and 240 Hz, respectively (60-cycle harmonics contribution, red arrows). These noise components seem to complicate the identification of the two typical OPs components located at ~75 Hz and ~150 Hz.
