Visual correlates of mobility in real world settings in older adults with low vision

Purpose. To determine the effects of reducing light level from photopic to mesopic on performance of real world mobility tasks and how performance of these tasks relates to measures of visual sensory and perceptual function. Methods. The visual functions, acuity, peak letter contrast sensitivity, visual field extent, glare disability, color confusion, motion sensitivity, spatio-temporal contrast sensitivity, scanning ability, and figure-ground discrimination were measured to determine their ability to predict mobility performance of visually impaired adults on indoor hallway and outdoor residential travel routes under photopic and mesopic lighting conditions. Results. Time to complete routes and number of mobility incidents were significantly increased under mesopic conditions. Depending on the task, lighting conditions, and performance measure, predictive models consisting of 4 vision variables were able to account for 30 to 42% of the variance in overall performance. The two most important variables in these models were visual field extent and scanning ability, followed by color confusion, grating contrast sensitivity, or spatial resolution. Conclusions. Reducing illumination levels from photopic to mesopic has an adverse effect upon mobility in older visually impaired adults. The aspects of vision which best predict performance include measures of sensory and perceptual visual function. The results compare well with those obtained under controlled laboratory conditions.