Effects of age-related macular degeneration and ambient light on curb negotiation.

Purpose: To determine how age-related macular degeneration (AMD) and changes in ambient light affect the ability to negotiate a curb while walking.

Methods: Ten older adults with AMD and 11 normal-sighted control subjects performed a curb negotiation task under normal light (∼600 lux), dim light (∼0.7 lux), and following a sudden reduction (∼600 to 0.7 lux) of light. In this task, subjects walked and stepped up or down a simulated sidewalk curb. Movement kinematics and ground reaction forces were measured during curb ascent and descent. Habitual visual acuity, contrast sensitivity, and visual fields were also assessed.

Results: Apart from slower gait speed in those with AMD, there were no differences between groups during curb ascent for any other measure. During curb descent, older adults with AMD frequently used shuffling steps in the approach phase to locate the curb edge and showed prolonged double support duration stepping over the curb compared with control subjects. However, reduced lighting, particularly a sudden reduction, led to several significant changes in movement characteristics in both groups. For instance, toe clearance stepping up the curb was greater, and landing force stepping down was reduced. In addition, slower gait speed and greater double support duration were evident in curb ascent and descent. In AMD subjects, contrast sensitivity, visual acuity, and visual field threshold were associated with several kinematic measures in the three light conditions during curb negotiation.

Conclusions: Minor AMD-specific changes in movement are seen during curb negotiation. However, attenuated lighting greatly impacts curb ascent and descent, regardless of eye disease, which manifests as a cautious walking strategy and may increase the risk of falling. Environmental enhancements that reduce the deleterious effects of poor lighting are required to improve mobility and quality of life of older adults, particularly those with AMD.