The kinetics of regeneration of rhodopsin under enzyme-limited availability of 11-cis retinoid.

In order to describe the regeneration of rhodopsin and the recovery of visual sensitivity following exposure of the eye to intense bleaching illumination, two models have been proposed, in which there is either a "resistive" or an "enzymatic" limit to the supply of retinoid. A solution has previously been derived for the resistive model, and here we derive an analytical solution for the enzymatic model and we investigate the form of this solution as a function of parameter values. We demonstrate that this enzymatic model provides a good fit to human post-bleach recovery, for four cases: for rhodopsin regeneration in normal subjects; for psychophysical scotopic dark adaptation in normal subjects; for rhodopsin regeneration and scotopic dark adaptation in fundus albipunctatus patients; and for cone pigment regeneration in normal subjects. Finally, we present arguments favouring the enzymatic model as the cellular basis for normal human rod and cone pigment regeneration.