Myopia rates among Hadza hunter-gatherers are low but not exceptional

Abstract

Objectives: Myopia rates are increasing globally. This epidemic is linked to increased school participation, decreased outdoor activity and the proliferation of near-work occupations. The Tanzanian Hadza have traditionally subsisted as hunter-gatherers. School participation has historically been low and near-work otherwise minimal. Previous studies have reported exceptionally low myopia rates among hunter-gatherers, though such studies are few. The present study aims to expand this dataset. We report Hadza myopia rates and compare them to those from other economic/subsistence niches. We look for temporal changes in eyesight, in line with changing Hadza subsistence. Further, we assess the impact two known myopia risk factors, gender and educational participation, on Hadza eyesight. Materials and Methods: We measured visual acuity among 182 bush-living Hadza aged 10–75 using a non-Latin optotype. From these measures, we estimate age-specific myopia prevalences. Results: We find age-specific myopia prevalences between 5% and 10% for individuals under 40, increasing thereafter. This is low compared to industrialized populations, although not atypical for rural and non-industrialized populations. Unlike previous studies of hunter-gatherers, myopia was not exceptionally rare. We find that Hadza men have better distance vision than Hadza women. Though the Hadza have experienced subsistence change, we find no statistical evidence of associated decreases in visual acuity between 2006 and 2013/14 after controlling for gender imbalances. Finally, we find no support for our prediction that schooling participation reduces visual acuity, though so few attended school (13 of 58) that this analysis lacked statistical power and probably represents a false negative.