Vision is important to both postural stability and to mobility, and visual impairment and postural stability may independently contribute to falls and a decline in physical functioning associated with aging. We propose to test the hypothesis that the role of vision in postural stability and falls is a dynamic one, interacting with other sensory impairments. We hypothesize that 1) loss of vision is profoundly associated with postural instability primarily in the presence of other sensory deficits, rather than when vision is the only sensory impairment; and 2) vision is an important compensatory strategy which is relied on heavily to minimize the effects of other sensory deficits on postural stability. We will test these questions by assessing the association of vision, somatosensory and vestibular function with postural stability and falls. Specifically, we will determine whether visual impairment is associated with postural stability in the presence of intact vestibular and proprioceptive senses, and whether a decrement in one sensory cue is compensated for by increased reliance on other sensory cues. We will then test whether visual impairment plus the loss of > other sensory cues interactively diminishes postural stability, compared to any one or none of these impairments. We will address these aims in both a laboratory-based and community setting. In the laboratory, we will test five groups of persons 65 and older with 1) no sensory deficits, 2) visual impairment alone, 3) vestibular deficits alone, 4) somatosensory deficits alone, and 5) visual impairment plus either vestibular or somatosensory impairments. These individuals will undergo baseline physiologic, and clinical testing of sensory functions and other independent contributors to postural stability, and measures of balance, mobility and physical functioning. A subset of these measures will be evaluated in the population-based study. Subjects in both populations will be followed prospectively for subsequent falls. We will seek to determine the independent and dynamic, interactive contributions of these sensory functions to both maintenance and loss of postural stability and to fall risk over time. This study will contribute to understanding the role of vision in postural stability and provide a model for vision as a physiologic compensation for deficits in other sensory cues to preserve postural stability. This information will provide a basis for clinical efforts to prevent or minimize the effects of these sensory impairments on postural stability and falls in older adults.