The Impact of Vision and Hearing Impairments on Health in Old Age

There are many poignant examples of how impairments in vision and hearing rob people of pleasure in life when they reach advanced old age. Persons who may be physically limited but who get a great deal of enjoyment from reading can lose this pleasure as a result of age-related macular degeneration. The enjoyment of social interactions with friends, spouse, children, and grandchildren is greatly diminished when hearing becomes severely impaired. The decline in quality of life related to vision and hearing impairments is reason enough to justify the vigorous search for better prevention and treatment. Additionally, there is increasing evidence, including the report by Reuben and colleagues in this issue of the Journal,1 that vision and hearing impairments have a broader impact on health outcomes than was previously suspected. Problems with vision and hearing are common even in those who have otherwise aged successfully. Numerous studies have documented the rapid rise in these impairments with age, with high rates of impairment at very old age. For example, in a large, population-based epidemiologic study in Beaver Dam, Wisconsin, the prevalence of vision impairment, defined as acuity of 20/40 or worse in the better eye, increased from 0.8% in persons aged 43 to 54 years to 21% in persons aged 75 to 86.2 The Blue Mountains Eye Study in Australia included very old persons and found the rate of visual impairment, defined in the same way, to be 42% in persons aged 85 to 97.3 The Beaver Dam Study also assessed the prevalence of hearing impairment and found a steep increase with age. Hearing impairment, defined as a pure-tone average of thresholds at 500, 1000, 2000, and 4000 Hz of greater than 25dB, was present in 83% of men aged 70 to 79, 97% of men aged 80 to 92, 55% of women aged 70 to 79, and 86% of women aged 80 to 92.4 Several previous studies, using both cross-sectional and prospective designs, have demonstrated that impairments in vision and, to a lesser extent, hearing, have an adverse impact on functional abilities. The report by Reuben et al. adds an important contribution to this literature by employing a cohort study that combines both self-reported and objectively measured sensory impairments with a long follow-up. The results are probably conservative estimates of the associations because the follow-up period was long (about 10 years), and there is no information available on change in impairment level in those classified as not impaired at baseline. Also, increased death rates in the initially impaired participants may lead to an underestimate of their risk for disability. The consistent results found for both self- reported and measured vision for multiple disability outcomes make a convincing case for these findings. The results for hearing impairment are less consistent. Both measured and self-report hearing impairment were associated with higher mobility disability but not disability in self-care or instrumental activities of daily living. This may be because the higher mobility items are more difficult tasks and, thus, more sensitive to sensory perturbations, or, perhaps, it is attributable to a more specific effect. For example, hearing impairment has been found to be associated with balance problems.5 The study by Reuben et al. also raises some intriguing questions about the impact of co-occurring impairments. There seems to be a synergistic effect of measured vision and hearing on basic self-care and higher mobility disability. In a recent paper, the impact of balance and strength impairments on walking disability was also shown to be synergistic.6 A great deal of effort has been expended trying to understand how co-morbidity affects older people, but developing methods that accurately reflect the burden of co-occurring diseases has been frustrating.7 A complementary approach, which may help to clarify the impact of multiple problems in older people, is the exploration of the joint effects of multiple co-occurring impairments. One advantage of this approach is that many impairments can be measured quantitatively; this gets around one of the issues that has most limited the study of co-morbidity, the standardized assessment of disease severity. The co-occurrence of diseases and impairments at a greater rate than expected by chance alone is also an area of potentially fruitful investigation. For example, in the Beaver Dam Study, 40% of the population aged 75 and older had both age-related maculopathy (ARM) and hearing loss, and there was a significant, 3-fold higher risk of hearing loss in those with late ARM compared with those without ARM.8 How can we explain the relationships of vision and hearing with disability? Three general areas to be considered include (1) the effect of underlying conditions and risk factors that affect both sensory loss and disability, (2) a direct effect of sensory loss on disability, and (3) an indirect chain of events whereby sensory loss leads to conditions that subsequently cause disability. If sensory loss results from conditions that also have a strong role in the development of disability, then impaired sensory organs may be innocent bystanders in the process of disablement rather than independent causes. Examples of risk factors for disability that also affect hearing include occupation, smoking,9,10 and cardiovascular disease.11 A great many systemic diseases affect the eye and also play a role in promoting disability. Diabetes, probably the most important example, causes diabetic retinopathy, increases incidence and progression of cataract,12 and has a direct effect on disability through the cardiovascular and neurologic systems. Although the data set employed by Reuben and colleagues does not provide information allowing for adjustment for less common diseases affecting both sensory loss and disability, the authors were able to adjust for many of the most important potential confounders, and it seems unlikely that confounding by unmeasured variables is the major explanation for the associations they observed. Sensory impairment, particularly visual impairment, has a direct effect on physical functioning. Severe vision impairment makes it difficult to perform a variety of activities and may lead to the need for help from other persons, particularly for tasks such as shopping and preparing meals. Beyond this obvious direct effect, however, are provocative findings that visual acuity does not tell the whole story when considering the direct impact of vision impairment on functional ability. In a study of older persons, visual acuity was associated with tasks requiring good resolution and adaptation to changing light environments, but judging distance, walking, and climbing stairs were significantly related to contrast sensitivity and not acuity.13 In a comprehensive study of the risk factors for hip fracture, both poor contrast sensitivity and reduced depth perception were modest but significant predictors of fracture occurrence, even after adjustment for bone mineral density and many other risk factors.14 In another study of hip fracture occurrence, an increase in risk was found for persons with good vision in one eye and moderate visual impairment in the other eye, but no increase in risk was seen in those with moderate impairment in both eyes.15 There is evidence that monocular impaired vision causes much greater loss of stereopsis than equal impairment in both eyes,16 and it has been found that to obtain stereopsis, visual acuity must be better than 20/40 in both eyes.17 Thus, to improve certain aspects of functioning, especially mobility in the community, it may be important to bring the vision in an older person's poorer eye up to the level of the better eye. Specific visual field impairments may also have a direct effect on mobility disability. In partially sighted persons, peripheral field loss impairs mobility more than central field loss, and the most important parts of visual fields for mobility are the left, right, and inferior midperiphery.17 Empirical evidence that documents the full sequence of events describing the indirect effects of sensory impairment on disability is lacking. However, piecing together findings on specific steps in the pathway from disease to disability provides support for the plausibility of indirect effects explaining the associations seen in the work of Reuben et al. Examples of this indirect effect are the known associations of sensory impairments with depression and social isolation and the potential impact of these intermediate outcomes on decreased activity, decreased exercise, and declines caused by disuse, all of which may subsequently lead to disability. An older person who becomes inactive and disengaged because of sensory impairments may not remain physically active enough to maintain the muscle strength and exercise tolerance necessary for long-term maintenance of higher level functioning. Clearly, a better understanding of this challenging area could point the way to effective interventions in people with declining vision and hearing. Sensory impairments are very common in old age, but their severity and impact may be ameliorated with appropriate care. It has been estimated that uncorrected refractive error and cataract each account for one-third of all visual impairment in older persons. Less amenable to treatment are the diseases that contribute to the remaining third, age-related macular degeneration, diabetic retinopathy, and glaucoma.18 Low vision rehabilitation services, which can be of great benefit for persons in this latter group, are underfunded and underutilized. There have been advances in hearing aid technology, and the majority of people with hearing loss find them beneficial.19 Persons receiving hearing aids show improvements in social, emotional, and cognitive function and communication compared with those with similar hearing impairments who do not receive hearing aids,20 and these benefits are sustained for at least a year.21 Nevertheless, hearing aid use remains low. In a community-based study, nearly 70% of persons with moderate to marked hearing impairment (pure-tone average threshold > 40 dB) did not use hearing aids.19 With ever increasing number of people living to advanced old age, the toll that sensory impairments take on quality of life and functional status is likely to increase. However, putting together the various pieces of this story — the high prevalence of sensory impairment, the many ways in which sensory impairment can affect functional outcomes, and the underutilization of effective treatments — points to the substantial benefits that could result from successfully reducing sensory impairments and their sequelae.