The electroretinogram recorded at the onset of dark-adaptation: understanding the origin of the scotopic oscillatory potentials.

The purpose of this study was to examine the origin of the oscillatory potentials (OPs) recorded at the onset of dark-adaptation. Our results show that following pre-exposure of the retina to progressively brighter photopic backgrounds there is a complete abolition of OP4 and approximately 50% of OP3, while OP2 is not affected in responses evoked to dim flashes of white light and recorded at the onset of dark-adaptation. These results bring further support to the claim that the short latency OP2 is cone-mediated while the OP3 and OP4 would have a significant rod contribution. However, a more complex picture of OP genesis arises when flicker and response to brighter white light flashes, also obtained within the first minute of dark-adaptation are considered. The latter would suggest that our understanding of the origin of the OPs cannot be exclusively based on which of the two class of photoreceptors is preferentially stimulated at the time the response is recorded.