Abstract
Abstract: :
Purpose:To study the refractive status of illiterate farm workers and an educated hospital staff and students in an isolated part of northeastern Brazil. This population is interesting because the small state of Alagoas has a highly mixed genetic ancestry dating back to colonial times but there has been little immigration during the past two hundred years so the genetically mixed populous is highly interrelated. Methods:The refractive status of 162 subjects was examined in a community of farm workers and 95 clerical staff and students at the Faculdade de Medicina, Universidade Federal de Maceio in the neighboring city of Maceio. The age range was restricted to 17 to 40 years. Refractions were performed with cycloplegic autorefraction. Only data for right eyes is presented. Results:Among the farm workers, myopia was rare. Only 7 eyes (4.3%) showed a myopic spherical equivalent of –1.0 D or more and the mean refractive error was +0.644 D. Among the hospital workers, 30.5% reached the –1.0 D criteria of myopia and the mean refractive error was –0.567 D. The means of these distributions and the prevalence rates of myopia differ significantly (P < 0.001). Each group contained one congenitally high myope (–8.62 D and –12.87 D, respectively). The illiterate group showed more hyperopia (≥ +2.0 D) (8.0%) than the hospital group (2.1%). Refractive status for both groups was independent of age (r = 0.04 and 0.06, respectively). The prevalence of astigmatism (≥ 1.0 D of astigmatism) was slightly greater for the farm workers (21.0%) than the hospital staff and students (12.6%) which is not to be expected since astigmatism is usually related to a higher prevalence of myopia. In both groups, astigmatism of 0.50 D or more tended to have more of a with–the–rule axis (53.4% and 51.3%, respectively) than an against–the–rule axis (29.5% and 30.8%, respectively). Conclusions:The low prevalence of myopia in the illiterate farm workers compared to the typical refractive profile for the educated sample of their interrelated neighbors indicates that myopia is related to literacy. The refractive distribution of this multi–ethnic illiterate group is very similar to that of the narrowly inbred illiterate indigenous people of the northwest Amazonas that has been previously reported.
Keywords: myopia • clinical (human) or epidemiologic studies: prevalence/incidence • refraction