normal hearing.49 Similarly, a population-based study involving 365 patients over the age of 70 living in a London borough found a significant relationship between depression and deafness that persisted even after controlling for age and socioeconomic status.18 There was no relationship, however, between the severity of the hearing impairment or disability and the severity of the depression.
In short, much of the work in this area is descriptive. The basic assumption made in all these studies—that poor hearing actually preceded the psychiatric disease—is not confirmed; this must be tested through a prospective study. A case-control study that controls for most potential confounders also has yet to be performed. Although later studies are suggestive, they are not definitive, and because many studies are done abroad, their results are not generalizable to all American populations. These issues are further obfuscated by a contradictory cohort study among elderly hospitalized psychiatric patients in England that did not show the expected association between paranoid and affective disorders and sensory deficits.34 This study has methodological limitations, however, similar to those already mentioned. Thus, the relationship between sensory impairments and serious psychiatric illness is only suggestive at best. Furthermore, the small samples of most studies do not allow comment on the relationship of an additional variable—that is, age.
Until very recently, the relationship between sensory impairments and cognitive deficits has been fraught with similar methodologic problems. Several studies have concluded that a relationship exists between either visual or hearing impairment and dementia.41,49,53,54,58 Other studies have not been able to document such a relationship.18,51 The lack of adequate controls, limited sample sizes, and heterogeneous definitions of both sensory impairment and cognitive deficits that characterize most of these studies makes it difficult to interpret their findings and come to any definitive conclusions. Recently, Uhlman conducted a case-control study involving 100 cases of Alzheimer's type dementia and 100 nondemented controls matched by age, sex, and education.54 This study reported a higher prevalence of significant hearing impairment (odds ratio, 2) among Alzheimer's cases. Even though the findings of the available studies do not allow definitive conclusions to be drawn with regard to the relationship between hearing impairment and cognitive decline, the Uhlman study adds weight to the suggestion that hearing loss is associated with cognitive dysfunction. A similar statement cannot as yet be made with regard to visual impairment and cognitive loss.49
Sensory loss disabilities have yet to be fully characterized, although the literature suggests several potential types. Surveys