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Bonnielin K Swenor, Karen Bandeen-Roche, Beatriz E Munoz, Sheila K West; Does walking speed mediate the association between visual impairment and self-report of walking disability? The Salisbury Eye Evaluation Study. Invest. Ophthalmol. Vis. Sci. 2014;55(13):191.
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To determine if performance speeds mediate the association between visual impairment and self-reported walking disability over an 8-year period.
2,520 Salisbury Eye Evaluation Study participants were followed 2-, 6-, and 8-years after baseline. Visual impairment was defined as best-corrected visual acuity worse than 20/40, or visual fields of approximately less than 20 degrees. Walking disability was assessed using self-reported difficulty on three tasks: walking up steps, walking down steps, and walking 150 feet. Performance speeds on three similar tasks were also measured: walking up steps (steps/second), walking down steps (steps/second), and walking 4 meters (meters/second). Generalized estimating equations were used to determine odds ratios (OR) and 95% confidence intervals (CI) comparing self-reported difficulty on each of the three mobility tasks among the visually impaired to the non-visually impaired over the 8-year study period. These models adjusted for years since baseline and baseline values for age, sex, race, smoking status, body mass index, presence of depressive symptoms, presence of diabetes, and the number of other comorbid conditions. Mobility performance speeds were added to the models to assess potential mediation.
For each year of observation, the odds of reporting mobility disability was significantly greater for visually impaired as compared to the non-visually impaired (OR difficulty walking up steps = 1.58, 95% CI: 1.32-1.89; OR difficulty walking down steps = 1.90, 95% CI: 1.59-2.28; OR difficulty walking 150 feet = 2.11, 95% CI: 1.77-2.51). Once performance speed on a similar mobility task was included, the difference in the odds of reporting mobility disability between the visually impaired and non-visually impaired was attenuated and no longer statistically significant (OR difficulty walking up steps = 0.84, 95% CI: 0.65-1.11; OR difficulty walking down steps = 0.96, 95% CI: 0.74-1.24; OR difficulty walking 150 feet = 1.22, 95% CI: 0.98-1.50).
The difference in the odds of reporting mobility disability between the visually impaired and non-visually impaired was largely accounted for by slower performance speeds among the visually impaired. This suggests that improving mobility performance in older adults with visual impairment may minimize the perception of mobility disability.
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