The first events in the visual process occur when light strikes the retina and photons are absorbed by photopigment molecules. The sequence of biochemical steps linking the input signal (light energy) to the first output signal in the visual system (electrical response of the photoreceptor) is the phototransduction cascade (in vertebrates, the cyclicGMP-cascade).
The components of the cGMP cascade are now known in sufficient detail that we can simulate phototransduction with explicit mathematical equations. The cascade involves activation and inactivation of several enzymes, as well as strong negative feedback mechansisms, which conjointly determine the overall sensitivity and dynamics of the electrical response of the photoreceptor. Below is a brief summary of the results.

Summary of the Results of the Present Study

The activation steps of the cGMP cascade are thought to be the most well understood. Here I present an analysis of the early rising phase of responses from both amphibian and primate (monkey & human) rods and cones. Results. I show that the activation of both rods & cones from these vastly different species are accounted for by a single linear model of activation of the cGMP cascade, requiring only a simple adjustment for the temperature difference between the species.