Dark adaptation and aging.

The literature relating aging and dark adaptation is discussed. The final threshold shows a significant rise in the increase in age which is more marked above the age of 60. The effects of stimulus hue (color), miosis, and the changes in the transmittance of the ocular media are explored as causes of the threshold rise. When the data are corrected for all of these effects, a threshold rise of about 0.5 log units remains which may be due to the interference in metabolism and to changes in the neural system.