We found a significant relationship between visual acuity decline and IADL decline over time in the elderly population-based participants of the SEE. A similar significant relationship between visual acuity decline and ADL decline over time among elderly men was also found. These relationships persisted even after controlling for demographic and health condition covariates at baseline and unobserved, within-person characteristics that did not change during the 8-year study. The mean change in best-corrected visual acuity over the 8-year study period was equivalent to a change from near 20/20 to near 20/25, and this change was coupled with a corresponding mean change equivalent to one-unit of increasing difficulty in two to three items of the IADLs. For instance, a participant with no difficulties with IADLs at baseline is likely to have developed a little difficulty in performing housework, preparing meals, and shopping for personal items.
Verbrugge and Jette proposed a Disablement Process model in 1994 that still serves as a useful framework for the maintenance of independence and the prevention or forestalling of disability.18
The presence of worsening pathology (e.g., progression of AMD) leads to impairment (e.g., declining visual acuity). Without vision-restoring treatment or adaptive accommodations to address this impairment, disability in the form of increasingly impaired ADL and IADL ensues. Left unchecked, disability levels increase, leading to reductions in quality of life, increased risk of transition to nursing home admission, and increased risk of death.19
The stronger associations found for visual acuity decline and IADL decline over time, which were consistent across categories of race and gender, also reflect the life-course perspective of the Disablement Process model, which posits that increasing levels of visual impairment will first impact IADLs.18
Previous research has also documented that visual impairment does impact IADLs more so than ADLs.20
However, as impairment increases, ADLs will also become impacted. Without intervention and with increasing visual impairment, these impacts worsen, increasing the likelihood that a person will need to move into a nursing home or will die.19
In addition, the strength of the association between loss in best-corrected acuity over time and IADL declines in our analysis was surprising (r
= 0.39 controlled for age, ); according to Jacob Cohen, this correlation corresponds to the midpoint between cutpoints for a large (0.5) and a moderate (0.3) effect size.21
By way of comparison, the 2-year development of new or worsening IADLs in Medicare beneficiaries based on baseline obesity levels found an increased risk among those in the extreme obesity category relative to individuals maintaining a healthy weight level (BMI >
versus 22.0–24.9 kg/m2
The odds ratio for men and women was 1.37 and 1.41, respectively, indicating effect sizes of less than 0.2.23
In our study, the association between best visual acuity loss and IADL decline (0.102, P
< 0.001, ) is stronger than that of obesity and IADLs (0.026, P
> 0.05, ).
Also surprising was our finding that the association between visual acuity decline and ADL decline over time was present only for men. Furthermore, the strength of the association for men was similar to that found for IADLs in all SEE participants, irrespective of race and gender (b
= 0.40, P
< .01). We could find no report in the literature that examined gender-specific comparisons of visual impairment trajectories and associations with change in any disability indicators. However, reports examining other gender-specific predictors of disability generally report greater impact on women versus men. For example, in a 2000 to 2006 study of 1634 elderly residents of Sao Paulo, Brazil, initially with no ADL difficulties, women with chronic diseases and social vulnerability experienced a greater incidence of disability than men after adjusting for socioeconomic status and health conditions on follow-up 6 years later.24
In the Swedish Panel Study of Living Conditions among the Oldest Old (SWEOLD), a nationally representative interview survey of persons aged 77 years and over, compared with men, women had significantly higher prevalence rates for most health indicators in both survey years, but there were no significant gender differences in ADL/IADL limitations. Prevalence rates increased significantly between 1992 and 2002 for all health indicators, but not for ADL/IADL.25
Given this limited body of research, there are no clear explanations for finding an association between visual acuity decline and ADL decline over time only among men. However, a traditional cultural emphasis on male self-reliance embedded within concepts of masculinity may interact with the increasing need to rely on the assistance of others in the face of visual acuity declines, leading to reduced feelings of self-efficacy.26,27
Lowered self-efficacy may, in turn, increase the likelihood that men are either more likely to report ADL declines or actually experience ADL reductions as they acquiesce to the increased challenges of functioning with declining vision.27
Although highly speculative, indirect support for this process comes from one report from the MacArthur Studies of Successful Aging in which higher levels of instrumental support (typically thought to be beneficial), were predictive of the onset of ADL disability in older men.27
Findings were strikingly different in men versus women. In multivariate models, instrumental support was typically protective for onset of ADL disability in women, although for most instrumental measures, these protective effects were not statistically significant. In men, there were several support indicators that were unexpectedly predictive of ADL onset. For example, odds of ADL disability onset was 6.86 in men reporting more than two episodes of instrumental support at baseline versus those reporting zero to two episodes. These findings suggest that future research on the longitudinal impacts of changes in visual acuity should incorporate vision-associated self-efficacy measures to determine if reductions in this domain may help to explain associations with changes in measures of disability and functioning.
Irrespective of the need for additional gender-specific research into associations between visual decline and ADL/IADL changes, other ocular research has documented that visual impairment is associated with quality of life indicators, including disability-free life expectancy,20
a finding consistent with the Disablement Process model.18
These findings point to the continuing need for research to identify strategies for primary prevention in order to avoid the development of potentially vision impairing ocular conditions such as AMD and glaucoma, as well as access to secondary prevention to limit the period of time persons are living with visual impairment from conditions amenable to vision restoring treatment (e.g., cataract surgery).28
However, findings also suggest that those with irreversible vision loss should have access to available aids to help mitigate the effects of living with this condition.29,30
There is increasing research showing that disabled elderly can regain functional ability so increased efforts at providing vision rehabilitation services may help to improve quality of life, but also to slow the disablement process.31,32
The mean best-corrected visual acuity in the SEE study decreased over an 8-year period from nearly 20/20 to nearly 20/25 with a decline of 2.9 letters. The visual acuity decline observed in the SEE is similar to the Blue Mountains Eye Study where the mean decline in best-corrected visual acuity over a 5-year period was 3.2 letters for participants aged 65 to 74 years at baseline and 6.3 letters for participants aged 75 years or older at baseline.33
In the Beaver Dam Eye Study, the mean decline in best-corrected visual acuity over a 15-year period for participants 75 years of age or older at baseline was approximately 3 lines of ETDRS acuity (14.9 letters).34
The greater decline in visual acuity loss in the Beaver Dam Eye Study compared with the SEE may be related in part to differences in race of participants, prevalence of ocular conditions, and follow-up rates.
The strength of our models assessing relationships in changes over time is that it provides a more rigorous test of causality than cross-sectional associations because it eliminates all potential confounders that are stable within the person. The method is a quasi-experimental design in that each individual is used as their own control.
Limitations of our study include the self-reported measures of ADLs and IADLs, which are influenced by an individual's assessment of his or her ability, the individual's expectation of that ability, and the individual's determination of the degree of difficulty in performing the task in the presence of limitations. However, we used standard questionnaires and in this way are no different from all other studies using self-reported data. While these models provide stronger tests of association by controlling for all static, within-person characteristics, they do not control for unobserved covariates that are changing significantly during the course of the study (except for age, ADL, IADL, and visual acuity). Unfortunately, we were unable to estimate the model using time-varying assessments of health conditions and controlled for baseline levels only. Therefore, changes in these health conditions since baseline were not accounted for in the models. Persons with severe cognitive impairment were not included in the SEE at baseline, to ensure that visual acuity could be measured on all participants in a standardized fashion. SEE retention efforts included offering abbreviated ocular examinations at participants' homes when participants were unable or unwilling to travel to the clinic site. However, some participants who dropped out because of entering a nursing home and those who died were likely to have greater increase in ADLs and IADLs, which may have caused an underestimation of the trajectories.
In summary, in this longitudinal study of older adults, visual acuity loss over time is related to increased difficulty with IADLs in women and men, and with increased difficulty in ADLs in men only. The findings indicate that reduced vision over time in the elderly is associated with significant functional decline, although it is important to note that unmeasured factors in our study may also play a role. Additional research is needed to identify ocular and nonocular factors that could help mitigate functional decline as visual impairment increases. This research will take on increasing importance as the demographic profile of the United States is undergoing a shift as the leading edge of the “baby boomer” generation started turning 65 in 2011.35
By 2030, this older proportion of the US population is expected to double to 72 million—in comparison with the number of older Americans in the population in the year 2000—leading to more Americans living with vision impairment.35
The emerging diabetes epidemic, in combination with these demographic shifts, is expected to increase the number of Americans living with diabetic retinopathy from 5.5 million in 2005 to 12.3 million by 2030.36,37
Finally, results suggest that additional efforts to prevent ocular conditions and complications that can lead to irreversible vision loss (e.g., glaucoma, diabetic retinopathy) are needed so that the proportion of future cohorts living with visual impairment is reduced over time.