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

Abstract

The study of the electrical response of the retina to a luminous stimulus is one of the main fields of research in ocular electrophysiology. The features of the first component (a-wave) of the retinal response reflect the functional integrity of the two populations of photoreceptors: rods and cones. We fit 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 affected 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 differ in the two cases and functions implying a different number of photocascade stages are necessary to achieve a correct modeling of the early phototransduction process. Numerical values of the parameters characterizing the best-fit functions are given and discussed.