Prevalence of myopia in Sherpa and Tibetan children in Nepal

Background. Tibetan and Sherpa children living in Nepal share a Common ancestry in Tibet and areas to the north of Nepal, but it is evident that these people experience widely contrasting educational and environmental conditions. The purpose of this study was to compare the prevalence of myopia in: children with similar genetic backgrounds but who are exposed to contrasting environments. Methods, Unaided vision and refractive error was measured in 555 Tibetan children-in Kathmandu and 270 Sherpa children in the Solu Khumbu region of Nepal. Results. There were marked differences in vision and the prevalence of myopia in the two groups. Ninety-two percent of the Sherpa children had Snellen vision df 20/22 (0.89) or better compared with 70%: of the Tibetan children, The range of refractive errors was -6.50 to +7.00 D for the Tibetan children and -1.00 to +3.50 D for the Sherpa children. The Sherpa children had a prevalence of myopia of 2.9% compared with 21.7% for the Tibetan children. Conclusions. The prevalence of myopia in Sherpa children is low and their rural lifestyle appears to be relatively unstressed. Tibetan children have a higher prevalence of myopia and more rigorous schooling. We did not establish a causal relationship between myopia and the type of schooling, or the environment in general, but we did demonstrate that a simple, rural lifestyle is at least compatible;with a virtual absence of myopia.