!"" CHAPTER FOUR her of cases, and percentage of blindness by age group. The rate of blindness increases by a factor of nearly one thousand, from less than 0.01 percent in preschool children up to 8.58 percent in people over the age of 60. Beyond age 60, age continuous to dominate other risk factors, as elderly individuals are increasingly at risk of developing cataract (See Chapter 6). TABLE 4-8. DISTRIBUTION, ESTIMATED NUMBER OF CASES, AND PREV- ALENCE OF BLINDNESS BY AGE GROUP (NBS 1981) Estimated Number of Cases Percentage of Nepal's Total Age Group Sample N Prevalence (per 100) 0-4 5-9 10-19 20-39 40-59 Over 60 Subtotal Missing 5,793 6,350 8,436 10,345 6,162 2,443 39,529 358 329 1,743 4,209 10,018 28,456 72,456 117,211 412 0.00 0.08 0.14 0.26 1.30 8.58 0.83 NA 0.3% 1.5 3.6 8.5 24.3 61.8 100.0 NA Total Source: 39,887 117,623 0.83 100.0 FR4.002 AN.17M There is an equally strong relationship between age and risk of traumatic unilateral blindness, reflecting the increasing blindness with age (see Chapter 9). These data are shown in Table 4-9 for unilateral blindness and in Table 4-10 for blindness in either one or both eyes. It should be stressed that the increasing prevalence of blindness with age acts to confound the relationship between the rate of blind- ness in the aggregate (from all causes) in several important predic- tor variables. For example, although many of the causes of blind- ness are_ linked to poverty (xerophthalmia, trachoma, etc.), the over- all blindness prevalence rates show no relationship at all to socioeconomic status. This is probably explained by age confound- ing. Higher socioeconomic status usually means longer life expect- ancy. With increases in life expectancy comes an increased risk of blindness due to cataract, trauma, and other conditions that represent cumulative lifetime risks. Thus communities with a greater share of elderly people will have higher blindness prevalence rates. Likewise, communities with a higher birth rate, lower life ex- pectancy, and a lower median age may have a lower blindness prev-
