Age Changes in Rate and Level of Visual Dark Adaptation

Abstract

Measurements of dark adaptation were made on 91 individuals aged 40-83 yrs. A Hecht-Shlaer adaptometer was used to measure the light threshold at 1- and 2-min. intervals for 30 min. after a 3-min. period of light adaptation. The individual curves were plotted in duplicate and independent observers made graphic fits for each portion of the dark adaptation curve. The slopes of the curves were computed for each subject. The correlation between the rates derived by the 2 investigators was 0.9 [plus or minus] 0.02 for both cone and rod adaptation rates. There was no correlation between age and either rate of cone adaptation or rate of rod adaptation. The cone threshold at 6 minutes and the rod threshold at 26 min. were both significantly related to age. It appears that the lowered sensitivity of the aged eye is not associated with a slower rate of adaptation. A tendency toward longer transition times between cone and rod vision appeared in the aged. However, the correlation between transition time and age was low.