Socioeconomic inequality in the global burden of refraction disorders: results from the Global Burden of Diseases Study 2017

Purpose To explore socioeconomic inequality in global burden of refraction disorders using disability-adjusted life years (DALYs). Methods World Bank categorical and national DALY numbers, crude rates and age-standardized rates caused by refraction disorders between 1990 and 2017 were obtained. Gini coefficient and concentration index were computed to assess trends in global health inequality in refraction disorders burden. Results Lower middle-income countries had the highest burden of refraction disorders and greatest decline in age-standardized DALY rates of 15.9% (171.0 in 1990; 143.8 in 2017), followed by upper middle-income countries, with a 9.7% decline (103.7 in 1990; 93.7 in 2017). High-income countries had the lowest age-standardized DALY rates (70.4 in 1990; 65.7 in 2017), while low-income countries had the lowest DALY numbers. Between-country inequality decreased, with Gini coefficient declining from 0.203 in 1990 to 0.184 in 2017. Socioeconomic-associated inequality also decreased, with concentration index changing from -0.060 in 1990 to -0.041 in 2017. Small peaks of DALY numbers and crude rates occurred in the age group of 5-9 years in countries with different income levels. An earlier occurrence of high peaks of DALY estimates in older adults had been observed in countries with lower income. Conclusion Middle-income countries are more burdened with refraction disorders but have achieved great progress in the last few decades. The global health improvement in refraction disorders has been accompanied by narrowing inequality. Older adults in lower income countries tend to suffer from refraction disorders at an earlier age, compared with older adults in higher income countries.