Contrast sensitivity in Alzheimer's disease: a 1-year longitudinal analysis.

Spatial contrast sensitivity was evaluated in normal elderly adults and a group with probable Alzheimer's disease (AD) in three sessions over a 1-year period. There was evidence of a reduction over 1 year in contrast sensitivity for static, high spatial frequencies in both groups of subjects. A striking difference between the subject groups was observed in their response to flickered stimuli. Although normal elderly adults yielded good stability in sensitivity for both static and flickered spatial frequencies over the 1 year, AD patients experienced a significant decline in response to flickered (7.5 Hz) stimuli. The significant decline in sensitivity for low contrast, high temporal events in AD patients is consistent with reports of cell loss at the retinal and cortical levels of the magnocellular (M) channel in AD. Thus, the spatial contrast sensitivity change in AD may reflect a more rapid loss of cells specifically in the M channel over a 1-year period.