A proximal retinal component in the primate photopic ERG a-wave

Area of Science:

• Neuroscience
• Ophthalmology
• Vision Science

Background:

• The photopic electroretinogram (ERG) is a key diagnostic tool in ophthalmology.
• The origin of the photopic a-wave, particularly its contribution from photoreceptors versus post-photoreceptoral cells, remains an area of investigation.

Purpose of the Study:

• To investigate whether the photopic a-wave in primate electroretinography (ERG) originates exclusively from photoreceptors.
• To elucidate the contribution of post-photoreceptoral retinal activity to the photopic ERG a-wave.

Main Methods:

• Photopic ERGs were recorded in monkeys using various flash stimuli.
• Intravitreal injections of glutamate analogs, APB and PDA, were administered to selectively block neuronal transmission.
• APB blocks depolarizing second-order neurons, while PDA blocks hyperpolarizing second-order neurons.

Main Results:

• Blocking hyperpolarizing second-order neurons with PDA partially eliminated the photopic a-wave.
• A PDA-sensitive component, likely postsynaptic to cones, determined the a-wave threshold and influenced responses to lower intensity stimuli.
• A non-PDA-sensitive component, presumed to be directly from cones, became dominant at higher intensities.
• PDA injections significantly reduced the photopic a-wave elicited by bright flashes, similar to those used in human clinical testing.

Conclusions:

• The primate photopic ERG a-wave is not solely derived from photoreceptors.
• A significant portion of the photopic a-wave arises from retinal activity postsynaptic to cone photoreceptors.
• These findings have implications for the interpretation of clinical ERG tests, especially those using stimuli near the ERG threshold.