A study of the human rod and cone electroretinogram a-wave component

The study of the electrical response of the retina to a luminous stimulus is one of the main \ufb01elds of research in ocular electrophysiology. The features of the \ufb01rst component (a-wave) of the retinal response re\ufb02ect the functional integrity of the two populations of photoreceptors: rods and cones. We \ufb01t the a-wave for pathological subjects with functions that account for possible mechanisms governing the kinetics of the photoreceptors. The paper extends a previous analysis, carried out for normal subjects, in which both populations are active, to patients a\ufb00ected by two particular diseases that reduce the working populations to only one. The pathologies investigated are Achromatopsia, a cone disease, and Congenital Stationary Night Blindness, a rod problem. We present evidence that the analysis of a pathological a-wave can be employed to quantitatively measure either cone or rod activities and to test hypotheses about their responses. The results show that the photoreceptoral responses di\ufb00er in the two cases and functions implying a di\ufb00erent number of photocascade stages are necessary to achieve a correct modeling of the early phototransduction process. Numerical values of the parameters characterizing the best-\ufb01t functions are given and discussed