Scotopic spectral sensitivity was measured for nine observers (aged 4.5 months to 66 years) from 400 to 650 nm (10-nm steps) by using a 42° naturally viewed stimulus. The dependent measure was the visually evoked cortical-potential amplitude that was phase locked to an 8-Hz flickering stimulus. Sensitivity was similar for all observers at middle and long wavelengths, but at short wavelengths there was a decrease in sensitivity with increasing age. The density of the preretinal ocular media was estimated by subtracting the log scotopic spectral-sensitivity function of each observer from the human rhodopsin-absorbance spectrum when the two sets of curves were pinned at long wavelengths. The density of the infant ocular media was lower than that for adults. To quantify the sequence of ocular-media development, scotopic sensitivity was determined for an additional 42 observers (aged 1 month to 70 years) at two spectral points: 553 nm, where the optic-media density is low, and 405–430 nm, where the density is high. From these data, optic-media density at 400 nm was calculated. Despite substantial individual differences within each age, a clear aging function emerged. Preretinal optic-media density increased monotonically from birth throughout adulthood. Thus optical density at 400 nm differs by about a factor of 22 between the average 1-month-old infant and the average 70-year-old adult.
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