Changes in the harmonic components of the flicker electroretinogram during light adaptation.

Purpose: To evaluate the nature and extent of changes in the fundamental and harmonic components of the 31-Hz flicker electroretinogram (ERG) during light adaptation.
Methods: Full-field ERGs were recorded from five visually normal subjects (ages 21-60 years). Following 30 min of dark adaptation, the subjects were exposed to a uniform adapting field of 50 cd/m(2). The field, which was presented for approximately 15 min, was intermittently modulated sinusoidally at 31.25 Hz. The ERG was recorded during the sinusoidal modulation, and Fourier analysis was used to obtain the amplitude and phase of the fundamental (F), second (2F), and third (3F) harmonic response components.
Results: F amplitude increased by almost a factor of two over approximately 6 min (time constant, τ, of 3.0 min). The 2F amplitude increased by a smaller amount, a factor of 1.4, and the time-course was approximately eight times faster than that of F (τ = 0.4 min). The 3F amplitude increased by a factor of 4.6, an increase that was larger than F or 2F, with a time-course that was between that of F and 2F (τ = 1.4 min). F phase was unaffected by light adaptation, whereas the 2F and 3F phases both increased by approximately 45° over similar time-courses (τ = 2.0 min).
Conclusions: Light adaptation had different effects on the fundamental, second, and third harmonic components of the 31-Hz flicker ERG, which resulted in a change in waveform shape during light adaptation. The previously reported flicker ERG amplitude growth is driven primarily, but not entirely, by changes in the fundamental.