The development of scotopic sensitivity

PURPOSE. Test the hypothesis that the developmental increases in rod photor eceptor sensitivity and rod-mediated visual sensitivity at 10 degrees, 20 d egrees. and 30 degrees eccentric are concurrent. It is known that maturatio n of the parafoveal (10 degrees eccentric) rod outer segments and visual se nsitivity is delayed compared to that at 30 degrees eccentric. METHODS. Rod isolated electroretinographic (ERG) responses to full-field st imuli were obtained from dark-adapted subjects (n = 71), ranging in age fro m early infancy through middle age. Rod photoreceptor sensitivity was calcu lated by fitting a model of the activation of phototransduction to the a-wa ve response. Rod driven b-wave sensitivity was calculated from stimulus-res ponse functions. A logistic growth model was used to summarize the developm ental increases in sensitivity of the rod photoreceptors and the b-wave. Pr eviously reported dark-adapted, rod-mediated visual sensitivities at 10 deg rees, 20 degrees, and 30 degrees eccentric. obtained using preferential loo king procedures, were reanalyzed using the logistic growth model. RESULTS. The logistic growth model accounted for 57% to 85% of the variance of etch sensitivity parameter with age in normal subjects. The shape of th e growth curve and the age at which sensitivity reaches 50% of the adult va lue is similar (10.0 -13.5 weeks) for the rods, the b-wave, and peripheral visual sensitivity, but is significantly older, 19.5 weeks, for rod-mediate d parafoveal visual sensitivity. CONCLUSIONS. Rod photoreceptor sensitivity and peripheral, rod-mediated vis ual sensitivity develop concurrently. A parsimonious explanation is that ro d photoreceptor sensitivity determines dark-adapted, rod-mediated visual se nsitivity during development.