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S. L. Christ, D. J. Lee, Ocular Epidemiology Group, Bascom Palmer Eye Institute & Dept. of Epidemiology, U. of Miami; Mechanisms and Moderators of the Visual Impairment and Mortality Association: The NHIS 1997-2000. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5210.
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Visual impairment (VI) increases the risk of mortality and depression. Depression also increases mortality risk. Some of the impact of VI on mortality may be mediated by depression. If so, the effects of VI on mortality will be understated when depression is specified as a simple control. In addition, these associations may be moderated by race and socio-economic status. The purpose of this study is to test depression as a mediator of the relationship between VI and mortality for income and race subpopulations.
Race and income sub-samples from the nationally representative National Health Interview Survey (NHIS) are used in a structural equation model to test the direct and mediated pathways between VI and mortality (n=166,204). A latent variable is used to measure the depression mediator based on the Psychological Distress Scale items (Kessler et al., 2002). VI is a self-reported measure of trouble seeing even with corrective lenses or unable to see at all. All model pathways control for age, sex, education, smoking, alcohol use, stroke, heart disease, joint problems, and emphysema. Parameter estimates and standard errors are adjusted for weighting, clustering, and stratification. Mortality parameters are adjusted for selection over time.
VI increases depression levels for all race and socio-economic subgroups (range: 0.25 - 0.66 of a standard deviation in the depression composite). For blacks and whites, but not other racial groups, VI increases mortality risk both directly and indirectly through depression. The direct effects [HR (95% CI)] are 1.32 (1.05, 1.66) and 1.23 (1.12, 1.36) and the mediated effects are 1.05 (1.00, 1.11) and 1.09 (1.07, 1.12) for blacks and whites, respectively. Similar pathways are operating for both income groups. For those earning less than $20,000 annually, VI increases mortality risk directly 1.15 (1.03, 1.27) and indirectly 1.06 (1.04, 1.08). For those earning $20,000 or more, VI increases mortality risk directly 1.33 (1.17, 1.51) and indirectly 1.09 (1.06, 1.12). The only subgroup difference is that the total effect (direct plus mediated effects) of VI on mortality is greater for the higher income group (p = 0.039).
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