Learning about retinal illuminance
and reduced color contrast and saturation helped me understand the added layer of difficulty the elderly face in navigating space.
FDT is quick, (33-42) relatively inexpensive and fairly robust to optical blur, (43) though it has also been found to be less robust to reduced retinal illuminance
, (44) a limitation when examining those with pupil miosis or cataract.
Relative scotomas were also mapped with the use of targets at the retinal illuminance level that was determined to represent the threshold sensitivity of the fovea or eccentric PRL.
The retinal illuminance of the stimuli is adjustable by 256 steps within the visible red-light laser range (50-50,000 Td).
The relationship between retinal illuminance
and contrast sensitivity to sine-wave gratings is summarily described as obeying DeVries-Rose and Weber's laws (Graham, 1989, Section 13.
A significant portion of this loss can be attributed to a decrease in retinal illuminance
caused by the age-related reduction in pupil size and the loss of lens transparency (Owsley, Sekuler, & Siemsen, 1983; Sloane, Owsley, & Alvarez, 1988).
The retinal illuminance
of a typical 60-year-old person is only one third that of a 20-year-old.
The FFFs of rasters scanned T-B were generally slightly lower than those for the other field scan directions, but the differences were not statistically significant at any retinal illuminance
(paired t tests).