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

R. A. Bush, P. A. Sieving

Research output: Contribution to journalArticlepeer-review

235 Scopus citations


Purpose. The monkey photopic ERG was studied during administration of glutamate analogs to determine whether the photopic a-wave derives exclusively from photoreceptors. Methods. Monkey photopic ERGs were elicited using 200-msec flashes or 30-μsec xenon photostrobe flashes on a steady light-adapting background of 40 cd/m2 (3.3 log scotopic troland). Intravitreal injections of APB, PDA, or both were given to block transmission to depolarizing and hyperpolarizing second-order retinal neurons, respectively. Results. After injecting PDA to block light responses of horizontal cells and hyperpolarizing bipolar cells, part of the photopic a- wave was eliminated. The PDA-sensitive component, presumed to be due to activity postsynaptic to cones, was responsible for the photopic a-wave threshold and dominated the response over the initial 1 to 1.5 log units of intensity. For brighter stimuli, this component made a constant contribution to the photopic a-wave. A non-PDA-sensitive contribution to the a-wave, presumed to originate directly from cones, was first evident 1 to 1.5 log units above photopic a-wave threshold. It progressively dominated the a-wave at higher intensities, particularly at early time points after the flash. Injecting PDA almost eliminated the photopic a-wave elicited with bright xenon photostrobe flashes that are commonly used for human clinical ERG diagnostic testing, indicating that this a-wave may contain significant postreceptoral activity. Conclusion. The primate photopic ERG a-wave derives, in part, from retinal activity postsynaptic to cone photoreceptors, particularly for stimuli near the photopic ERG threshold that are typically used for human clinical studies.

Original languageEnglish (US)
Pages (from-to)635-645
Number of pages11
JournalInvestigative Ophthalmology and Visual Science
Issue number2
StatePublished - 1994
Externally publishedYes


  • 2-amino-4-phosphonobutyric acid
  • a-wave
  • Cis-2,3-piperidine-dicarboxylic acid
  • cones
  • depolarizing bipolar cells
  • electroretinography
  • hyperpolarizing bipolar cells
  • photopic ERG
  • primate

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience


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