![]() ![]() The prevalence of blindness in the population is greatest in the older age categories. ![]() That calculation or estimate is shown for the years 19 in Table 1. The number of cases of blindness for different age categories can be calculated by multiplying the prevalence rate times the population count for each age category. ![]() Although the estimates have many limitations, we use statistics on the prevalence, incidence, and demographic characteristics of legal blindness in the United States in the next section to describe the legally blind population. The field of nonmedical rehabilitation, in fact, aims to reduce the disabilities associated with given impairment and justify the need for individual rehabilitation plans. Very often two people with identical impairments have markedly different disabilities. Specific types or degrees of impairment reveal very little about disability for any individual person. It does not take into account other visual factors, such as sensitivity to glare or light and dark adaptation, that also affect mobility and other visual tasks. Legal blindness is defined in terms of two aspects of visual impairment, acuity and field size (i.e., acuity of 20/200 or worse in the better eye with correction or a visual field of 20 degrees diameter or less). The measure that is most readily available to draw a demographic profile, legal blindness, suffers in that it does not address many relevant factors that contribute to disability. Psychosocial factors, such as access to support groups and rehabilitation services and income level, are important predictors of disability for which there are few available data. ![]() We are forced to make estimates that may be out of date or unrepresentative as well as not focused on the most pertinent determinants of disability. Unfortunately, available statistics on the blind population are grossly inadequate. Demographic information about the visually impaired population in terms of pathology, impairment, and handicap is important mainly in terms of its relevance to mobility tasks. Our focus in this report is on disability-i.e., the limitations of visually impaired people in carrying out the tasks of mobility. There are also likely to be varying degrees of overlap among the groups defined in this way. The size and demographic characteristics of that population will presumably be different depending on which of the concepts is under study. Whatever criteria are used to identify the population of visually impaired people in the United States, there are several ways to classify subgroups of that population in relation to their probable use or nonuse of mobility aids. At this level, the characteristics of the social environment, including socioeconomic resources, discrimination, and characteristics of the individual, are involved. Handicap refers to limitations in performing social roles (socially structured sets of tasks). At this level of analysis, the individual and inevitably such factors as motivation, training, and the resources (aids) available to help accomplish tasks are involved. Disability refers to limitations in carrying out tasks. Impairment refers to lasting consequences of pathology, affecting parts of the organism. 1īriefly defined, pathology refers to a medically determined disease or disorder (including trauma, structural abnormality, etc.). Athough terminology may vary, agreement has emerged around a set of four concepts: pathology, impairment, disability, and handicap. In disability-related research and policy generally, some common definitions have been developed to describe all types of impairment. ![]()
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