Sensitivity of human foveal color mechanisms throughout the life span.

Spectral sensitivities of mechanisms dominated by short-, middle-, or long-wavelength-sensitive cones were measured for 76 observers ranging in age from 10 to 84 years. The short-wavelength mechanism was isolated with a yellow adapting background and five test wavelengths between 420 and 550 nm modulated at 2 Hz. Sensitivity declined with age, but the slopes of the functions varied as a function of wavelength. When the data were corrected for light losses in the ocular media, the slopes were similar for lambda less than or equal to 500 nm and still significantly correlated with age. At 440 nm, the sensitivity of the short-wavelength mechanism, specified at the retinal level, declined at a rate of 0.08 log unit per decade. Sensitivity at 550 nm under these conditions was dependent on middle- and/or long-wavelength-sensitive cones and was not correlated significantly with age. To study isolated middle- and long-wavelength mechanisms, sensitivities were measured at six wavelengths between 500 and 650 nm, using a 20-Hz test stimulus and appropriate chromatic adapting backgrounds. The sensitivities at all wavelengths were correlated negatively with age. When specified at the retinal level, the sensitivity at 560 nm declined at a rate of 0.11 log unit per decade for both middle- and long-wavelength mechanisms. These data support the view that the sensitivities of all three cone types and/or at least one of their postreceptoral pathways declines from 10 to 84 years of age.