Impact of visual function changes on mortality through changes in activities of daily living (ADL) and instrumental activities of daily living (IADL) among aging adults

Background: Repeated studies have shown that visual impairment is associated with increased risk of mortality, but the mechanism is unclear. Methods: A population-based sample in Salisbury, Maryland of 2520 white and black individuals, aged 65–84 years in 1993-1995 were re-assessed 2, 6, and 8 years later with mortality follow-up through 2009. Best-corrected ETDRS visual acuity (VA) was obtained. ADL and IADL were surveyed. VA and ADL/IADL trajectories were estimated for each respondent using OLS regression. Structural equation modeling estimated the associations among the trajectories and mortality while controlling for demographic and health covariates. Results: ADL difficulties increased by 0.16 standard deviations (SD) and IADL difficulties increased by 0.27 SD annually. In multivariable models, poorer VA at baseline was associated with worse IADLs at baseline (p < 0.001) and with worsening ADLs (p<0.01) and IADLs (p< 0.05) over time. Declining VA was associated with worsening IADL (p<0.001). For a one SD annual rate of increase in IADL the hazard of death is increased by 1.70 (p < 0.001). Visual acuity trajectories did not directly predict mortality. However, a one logmar unit annual rate of change in VA increased mortality by 77% (HR:1.77; 95% CI:1.33-2.35) through worsening IADLs. Conclusions: The impact of visual impairment and visual impairment changes in older adults on mortality operates in part through increases in IADL. Aside from preventing visual declines it may also be important to target those with visual impairment for interventions designed to reduce IADL declines.