varying definitions of visual impairment affect the magnitude of its incidence and prevalence. The National Health Interview Survey defines visual impairment as the ability to read newsprint. According to this measure, preliminary data indicate that approximately 13 percent of noninstitutionalized Americans aged 65 and older have some form of visual impairment.23 Of this group, 8 percent suffer with a severe impairment, which is defined as the inability to read newsprint even with glasses.39 The severely impaired therefore also include those who are blind in both eyes.39 The survey reports that 3.2 percent of respondents reported blindness in one eye, and 1 percent reported blindness in both eyes.23 Legal blindness, on the other hand, is defined as 20/200 vision or worse. (An eye with 20/200 vision sees at 20 feet that which an eye with 20/20 vision can see at 200 feet.) Confident estimates of the prevalence of legal blindness, however, are not available.
If one defines poor visual acuity as anything equal to or worse than 20/50 vision, the incidence of visual loss increases by 13 percent between ages 60 and 69 and 32 percent among those 70 to 80 years old.42 Using the same definition (20/50 or worse), 11 percent of persons aged 65 to 73 who wear glasses are impaired; 26 percent of this age group who do not wear glasses are also impaired.38 By 80 years of age, only 10 to 20 percent of this group will have a visual acuity of 20/20.42 Performance on tests of stereoscopic acuity decrease from nearly 100 percent at age 30 to approximately 60 percent at age 80.42 Performance on red-green color match tests decrease from 60 percent at age 30 to less than 10 percent at age 70.42
Hearing loss is also measured using different definitions and therefore yields varying prevalence estimates as well. Using a threshold of 40 decibels (dB) (speech is generally at the 50-dB level—see Figure 7-1) for any two measured frequencies, the prevalence of hearing impairment is 45 per 100,000 for those 17 to 44 years of age, 119 per 100,000 for those 45 to 64 years of age, and 282 per 1,000 for those over 64 years of age.6 Preliminary data from the National Health Interview Survey show a similar distribution in the population aged 64 and older; they also indicate that hearing impairment (defined as ''the reported presence of deafness in one or both ears or any other trouble hearing"23) varies with age and sex. Twenty-three percent of individuals aged 65 to 74, 32.7 percent of those 75 to 84, and 48.4 percent of those 85 and older show hearing impairment. Men had a greater percentage of hearing impairments in each age range. For example, among those 65 to 74 years old, 30 percent of the men were impaired as compared with 17.5 percent of the women.23 Other studies that focus on sensory loss among specific populations (e.g., nursing home residents) have found even higher prevalence rates.3,19,47 For example,