Densitometric measurement of human cone photopigment kinetics

We measured the radiance response function for steady state bleaching lights and the regeneration of the cone visual photopigments using the continuous recording densitometer described by v. Norren and v.d. Kraats. Measurements made on 5 deuteranopes, 1 protanope and 2 color-normal observers were similar. The radiance response function was steeper than the function predicted by a simple first-order kinetic equation. For a measured density (ca 0.3) we evaluated whether high stray light (ca 47.5%) and high two-way optical density (ca 1.3) could account for the deviation from the prediction of a first-order equation. Such a model was rejected because these parameters predicted different estimates of the time course of regeneration for different test wavelengths (554 and 605 nm). Statistical analysis of the regeneration data revealed a highly significant non-linearity. A model in which the rate of regeneration increases as the proportion of bleached photopigment decreases is required to explain both the radiance function and the regeneration data.