Functional analysis of Normal and CSNB a-wave ERG component

The features of a-wave of the human electroretinogram are one of the more debated problems in electrophysiology since the a-wave reflects the functional integrity of the two photoreceptoral populations (rods and cones). Although different models concerning the contributions of the early photoreceptoral response are available in current literature, a fully comprehensive theory is difficult to formulate because of the large amount of individual photoreceptors. We study the kinetics of the photoreceptoral response through the analysis of the a-wave shape both in healthy and in patients affected by the Congenital Stationary Night Blindness, that interests the rod population only. The physiological behavior has been explored by modeling the a-waves with a set of appropriate statistical functions, representing all possible mechanisms governing the interactions occurring in the phototransduction process. The results indicate that in healthy subjects, correlations between photoreceptoral populations take place, as a consequence of direct cell-to-cell interactions among rods and/or cones and a sum of Gaussian-Lorentzian functions is appropriate. In pathological subjects the best fit is obtained using the Symon-Vavilov function, that is suitable to simulate coherent responses in situations affected by fluctuations.