Light adaptation and the luminance-response function of the cone electroretinogram.

Cone electroretinograms are typically isolated by presenting stimulus flashes against rod-desensitizing adapting fields. To investigate the manner in which adapting-field luminance affects cone electroretinogram response properties, we measured cone electroretinogram luminance-response functions of two normal subjects, with stimuli presented against adapting fields that ranged in luminance from -1.2 to 2.1 log cd/m2. A flicker rate of 31.1 Hz was used to isolate cone electroretinograms under all adaptation conditions. A hyperbolic equation of the form (R/Rmax) = Ln/(Ln + Kn) was fitted to each luminance-response function by a least-squares criterion. As adapting field luminance increased, the best-fit values of the variables K and n increased, which is in general agreement with results of electrophysiologic studies of light adaptation in retinal neurons. However, Rmax values also increased with adapting field luminance. The change in all three of these variables with adapting field luminance must be considered in the interpretation of cone electroretinogram luminance-response functions from patients with retinal disorders.