The visual system can adapt to lights and can function over a wide range of light levels. It accomplishes this by adjusting its light sensitivity relative to the ambient level of light. The mechanisms underlying light adaptation are largely retinal in origin. We concentrate our research, using psychophysical and noninvasive electrophysiological techniques, on studying the sites, i.e., the retinal levels involved, and the mechanisms of light adaptation. The information gained from these studies in the normal visual system is then used to test hypotheses about how disease affects the visual system.

We have just completed a study of patients with an inherited retinal degenerative disease characterized by increased sensitivity of the short-wavelength-sensitive (S) cone system. Our purpose was to test the hypothesis that the retinas of patients with this syndrome have more S-cones than those patients with normal retinas. To conduct this research, the results of noninvasive electrophysiological techniques, i.e., electroretinogram responses, were compared to results obtained using psychophysical techniques. The data which were analyzed within the context of a model of the S-cone system were consistent with the presence of more S-cones and S-cone ganglion cells and with a decrease in the L- and M-cone input to each S-cone ganglion cell.