Sites of age-related sensitivity loss in a short-wave cone pathway.

The age-related losses in the sensitivity of a short-wave (S) cone mechanism were determined by measuring the threshold-versus-radiance (t.v.r.) functions for nine older (mean age, 71.0 years) and six younger (mean age, 24.4 years) subjects. Measurements were obtained for a 250-ms, 1.03 degrees-diameter, 440-nm foveally viewed test light presented on 470-nm adapting fields and on a 570-nm auxiliary field. A comparison of t.v.r. functions revealed intensity-dependent sensitivity losses in the older group. By applying a quantitative model of an S-cone pathway to the t.v.r. data obtained from the older subjects, we found that the age-related changes in the ocular media and the receptor sensitivities can account for much but not all of the difference in the sensitivity of an S-cone mechanism demonstrated by eight of our nine older subjects.