Studies were conducted on normal subjects to evaluate amplitude and implicit time of the major components of the human electroretinogram (ERG) at the beginning and after 24 minutes of dark adaptation. All components gain amplitude during the course of dark adaptation. The components, N-2 (A-2), B-1, and B-2 were found to have an increasing implicit time while that of N-1 (A-1) and P-2 remain stationary. The constant implicit time of P-2, in opposition to other components, sets it apart as a different function. The A wave is described as unique and of increasing implicit time as the other components of the ERG. The interaction of this positive deflection, of constant latency and implicit time, and a single A wave with an increasing amplitude and implicit time, can explain the apparent double A wave.
Brunette JR. The Human Electroretinogram During Dark AdaptationImplicit Time and Amplitude Studies. Arch Ophthalmol. 1969;82(4):491-498. doi:10.1001/archopht.1969.00990020493015