Aging and neural spatial contrast sensitivity: photopic vision.

This study investigated the extent to which older adults' loss in spatial contrast sensitivity at a photopic level is attributable to neural changes in the aged visual system. Laser interferometry was used to generate interference fringes which bypass the optics of the eye in presenting a grating target on the retina. Older adults in good eye health exhibited on average a small but statistically significant loss (0.1-0.2 log unit) in contrast sensitivity across the spatial frequency range tested, although there was considerable overlap between young and old adults. This loss in contrast sensitivity for interference fringes accounted for less than half of the photopic contrast sensitivity loss at higher frequencies reported for older adults in studies using conventional direct-viewing techniques in which the optics of the aged eye are not bypassed. We conclude that neural changes in the aged visual system have a rather minor contribution to older adults' loss in spatial contrast sensitivity at a photopic level.