Retinal Illumination and Age

As our eyes age the amount of light reaching the retina decreases. This is attributable largely to changes in the pupil diameter, to the yellowing of the lens and, to a smaller extent, to a change in the effective path-length of light through the lens. The age variation of retinal illumination is estimated on the basis of published data for standard illuminants A and C, and for three types of fluorescent lamp. In all five cases the small difference found to exist between the light-adapted and dark-adapted eye is greater than differences between the lamps considered. In general, retinal illumination at the age of 60 is about one-third of the value corresponding to an age of 20. The practical significance of the estimate is discussed.