This study provides an overview of the global pattern of the health burden of cataract vision loss by year, age, sex, region, and socioeconomic levels. From 1990 to 2015, the DALY number of cataract vision loss increased by 89.42%. The age-standardized DALY rate increased before 2005 and then decreased slowly to the 1990s level. The health burden of cataract increased rapidly in people over 50 years of age. Females had a higher health burden compared to males at the same age. The health burden of cataract vision loss is closely associated with socioeconomic factors, even after adjusting for demographic and environmental factors.
Although prevalence data and DALY could not be compared directly, both types of information have implications for understanding the situation of cataract vision loss. It was estimated that the prevalence of cataract vision loss was decreasing during the period between 1990 and 2010 in all countries, with the exception of eastern Sub-Saharan Africa.
1,11 From 1990 to 2010, the number of people with cataract blindness was reduced by 11.4%, and the percentage of blindness due to cataract decreased from 38.6% to 33.4%. This may be associated with global action such as VISION 2020, which set cataract as a priority, and national programs such as the China Million Cataract Surgeries Program.
12 However, the improvement in prevalence did not mean a lesser health burden of this condition, as our study demonstrates. The DALY number increased continuously, which may be due to the population growth and elongation of life expectancy. As shown earlier, the DALY was closely associated with population number and life expectancy. In the past 25 years, population and life expectancy increased by approximately 30% and 16%.
13 The life expectancy factor contributed to 38.9% of the variation in age-standardized DALY rate across countries (
Table 1). However, the educational factor was more influential and accounted for 55.6% of global variations in age-standardized DALY rate. Therefore, regarding the observation that the health burden of cataract blindness increased during the past decade, it is unlikely that it changed if one considers the changes in life expectancy.
The outcomes and potential complications of cataract surgery were also key components of blind prevention projects. The outcomes in low-income countries are very low compared to those in high-income countries.
14 There are several possible causes of poor outcomes of cataract surgery in low-income countries: (1) problems of biometry and availability of intraocular lenses fitted for each patient; (2) postoperative opacification of the capsular bag without YAG laser access; (3) poor surgical techniques; (4) endophthalmitis related to the lack of sterile conditions; and (5) other classic complications (retinal detachment, cystoid macular edema, and so on). For example, it was reported that 0.39% of patients experienced retinal detachment after cataract surgery in Denmark, while the risk was 0.47% for patients in China.
15,16 These findings reinforced sustained demands for allocating resources to cataract services and monitoring the quality of cataract surgery.
We observed a disproportionate distribution of the health burden of cataract. A previous study demonstrated that cataract ranked as the most unevenly distributed eye disorder in 2004, with higher DALYs in low- and middle-income countries.
17 The World Health Survey in 70 countries showed that the prevalence of vision difficulty in low-income countries was two times higher than that in high-income countries.
18 Among the 21 Super Regions, the prevalence of cataract blindness was highest in Oceania, followed by South and Southeast Asia, and the lowest in high-income countries.
1 Consistent with previous studies, the present study observed an unevenly distributed health burden of cataract. The levels of health burden in Southeast Asia, the Eastern Mediterranean, and Africa were higher than the global level; addressing this should be a priority in future programs.
The national HDI level was independently correlated with the health burden of cataract vision loss, with higher age-standardized DALY rates in lower HDI countries. HDI reflects the quality of wealth, which has become a standard indicator for comparisons of socioeconomic development across countries. The economy may be implicated as one possible determinant of output and quality of cataract surgery.
9 The number of ophthalmologists per million people varied with socioeconomic development, with higher concentration in regions with higher HDI and per capita gross domestic product.
19–21 Globally, the preoperative visual acuity with regard to cataract surgery was associated with increasing HDI and per capita income.
22,23 The cost was the main barrier to utilization of cataract surgery in some developing countries.
24–26 Reduction of the cost effectively increased the cataract surgical rate in southern China by 160%.
27 More free or low-price surgeries are needed to reduce the health burden of cataract vision loss.
28
The educational factor was found to be the most prominent HDI component. It was previously reported that increased knowledge was associated with accepting cataract surgery, whereas cost and transportation were not.
29 This may be explained by the following reasons. First, high education usually means better knowledge of cataract. Willingness to pay for cataract surgery has been reported to increase with knowledge of cataract.
30,31 Secondly, higher education leads to a higher possibility of a steady occupation, as well as higher income and coverage by medical insurance, enabling the cost of cataract surgery to be more affordable. Even in the United States, annual use of eye services was significantly associated with levels of educational attainment after adjusting for other factors.
32–34 A randomized controlled trial demonstrated that educational interventions can successfully increase the uptake of cataract surgery.
35
Sex differences in the health burden of cataract vision loss were significant for each age group. One possible explanation is that females have a higher incidence of cataract and longer life expectancy. Another explanation may be related to sex inequality in relation to utilization of cataract surgery. Evidence suggests that females are less likely to access eye health, especially in developing countries. Though 60% of cataract blindness was in females, males had 1.39 times odds of uptake of cataract surgery compared to women.
36,37 Being female usually was related to a higher rate of illiteracy, especially among the elderly, and less control of finances compared to men, which prevented opportunities for operations.
36–39 For children with bilateral cataract, access to surgery for girls was also lower than for boys in low-income countries.
40 After adjusting for other factors, being female was found to be associated with poor uncorrected visual acuity (
P = 0.04) and corrected visual acuity (
P = 0.03) post cataract surgery.
12 Closing sex disparities in cataract surgical services would be beneficial with regard to improving the health burden of cataract.
This study has limitations. First, the accuracy of health burden information suffered from the limitations of the data sources. For example, statistical assumptions may introduce bias.
6,7 Second, the analytic unit was at the national level rather than the district level, which may introduce the ecologic fallacy. Significant variations in development levels and disease burden may exist within a country.
41,42 Finally, subgroup analyses by culture and health system factors were not performed, as corresponding data for these fields were unavailable. Notwithstanding the above limitations, the findings of this study could serve as an impetus for continued efforts toward eliminating cataract blindness.
To conclude and in summary, the global health burden of vision loss related to cataract increased between 1990 and 2015 despite considerable efforts in the form of the WHO and VISION 2020 initiatives. Older age, being female, less education, and poor socioeconomic status were associated with a higher burden of cataract vision loss. These findings can raise awareness of the disease burden of cataract and could serve as impetus for continued efforts toward eliminating cataract blindness.