Cone phototransduction and growth of the ERG b-wave during light adaptation.
The purpose of this study was to determine whether cone redepolarization accounts for the amplitude increase of the b-wave of the human electroretinogram (ERG) during light adaptation. The time course of the b-wave amplitude increase was compared to the time course of the change in the activation phase of cone phototransduction, as derived from a delayed Gaussian model applied to the leading edge of the ERG a-wave. ERG recordings were obtained from five visually normal subjects, alternately in the presence of the adapting field (adapt-on condition) and 300ms after its temporary extinction (adapt-off condition). The proportional increase in amplitude was less for R(mp3) (maximum amplitude of P3, the massed cone photoreceptor response) than for the b-wave for both adaptation conditions, and the time course of the amplitude increase for R(mp3) was faster than that for the b-wave in the adapt-off condition. The results demonstrate that time-dependent changes in the activation phase of cone phototransduction have only a minimal role in governing the increase in the amplitude of the human cone-derived ERG b-wave during light adaptation. In addition, the systematic increase in b-wave amplitude and the decrease in b-wave implicit time in the adapt-off condition indicates that the ERG response measured shortly after adapting field offset does not necessarily represent the waveform of the dark-adapted cone ERG.
Alexander
Kenneth R
KR
Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, 1855 W. Taylor St., Chicago, IL 60612, USA. kennalex@uic.edu
Raghuram
Aparna
A
Rajagopalan
Aruna S
AS
D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D003623:Dark Adaptation; D004596:Electroretinography / Q000379:methods; D005260:Female; D006801:Humans; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology*