November 2016
Volume 57, Issue 14
Open Access
Clinical and Epidemiologic Research  |   November 2016
Global Patterns in Health Burden of Uncorrected Refractive Error
Author Affiliations & Notes
  • Lixia Lou
    Department of Ophthalmology, The Second Affiliated Hospital of Zhejiang University, College of Medicine, Hangzhou, Zhejiang, China
  • Chunlei Yao
    Department of Ophthalmology, The Second Affiliated Hospital of Zhejiang University, College of Medicine, Hangzhou, Zhejiang, China
  • Yanhua Jin
    Department of Ophthalmology, Dongyang People's Hospital, Dongyang, Zhejiang, China
  • Victor Perez
    Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, United States
  • Juan Ye
    Department of Ophthalmology, The Second Affiliated Hospital of Zhejiang University, College of Medicine, Hangzhou, Zhejiang, China
  • Correspondence: Juan Ye, Department of Ophthalmology, The Second Affiliated Hospital of Zhejiang University, College of Medicine, Jiefang Road 88, Hangzhou, 310009, China; yejuan@zju.edu.cn
  • Footnotes
     LL and CY contributed equally to the work presented here and should therefore be regarded as equivalent authors.
Investigative Ophthalmology & Visual Science November 2016, Vol.57, 6271-6277. doi:10.1167/iovs.16-20242
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Lixia Lou, Chunlei Yao, Yanhua Jin, Victor Perez, Juan Ye; Global Patterns in Health Burden of Uncorrected Refractive Error. Invest. Ophthalmol. Vis. Sci. 2016;57(14):6271-6277. doi: 10.1167/iovs.16-20242.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Abstract

Purpose: To evaluate the global patterns in health burden of uncorrected refractive error (URE) by year, age and sex, region, and socioeconomic status, using disability-adjusted life years (DALYs).

Methods: Global, regional, or national DALY numbers, crude DALY rates, and age-standardized DALY rates caused by URE, by year, or age and sex, were obtained from the Global Burden of Disease Study 2013. Human development index (HDI) in 2013 as a national socioeconomic indicator was obtained from the Human Development Report. Kruskal-Wallis test and linear regression were performed to explore the association between age-standardized DALY rates and HDI.

Results: From 1990 to 2013, global DALY numbers caused by URE rose by 43.8%, crude rates remained relatively constant, and age-standardized rates fell by 8.8%. Global DALY rates increased with age, and older females had higher DALY numbers and rates than males of the same age. Age-standardized DALY rates in Eastern Mediterranean, South-East Asia, and Africa were higher than that at a global level. Multiple comparisons indicated higher age-standardized DALY rates in lower HDI countries. Age-standardized DALY rates were inversely related to HDI (standardized β = −0.616, P < 0.001).

Conclusions: The global health of URE is improving but crude DALY rates are keeping constant, implying that health progress does not mean fewer demands of refractive services. Worldwide, older age, female sex, and lower socioeconomic status are associated with higher URE burden. The findings of this study may raise public awareness of the global URE burden and are important for health policy making.

Uncorrected refractive error (URE), which affects a large proportion of the world population, is the major cause of vision impairment and the secondary cause of blindness.1,2 The Global Burden of Disease (GBD) Study 2010 estimated that in 2010, 101.2 million cases of moderate and severe visual impairment (MSVI), and 6.8 million cases of blindness were due to URE.2 Uncorrected refractive error may reduce educational opportunities, productivity, and overall quality of life.35 The potential productivity loss from visual impairment due to URE (VI-URE) in 2007 was estimated to be 269 billion international dollars (I$), which is over 1000 times greater than the global prevalent cases of VI-URE, implying that providing refractive services less than I$ 1000 to each affected person would result in a net economic benefit.5 However, despite the relatively low cost of refractive services such as spectacles,6 the prevalence of URE remains high worldwide, which may be partially attributable to the shortage of well-trained optometrists and opticians. Several population-based studies conducted in specific regions and age groups had revealed great disparity in prevalence of URE. Defining URE as a presenting visual acuity of less than 6/12 in the better eye with improvement of at least 0.2 logMAR (equivalent to 2 lines) after refraction, prevalence rates of 21%,7,8 15%,9 and 10%10 were found in Singaporean Chinese or Malays, American Latinos, and Caucasian Australians, respectively. 
Visual impairment due to URE is the leading and most easily preventable cause of disability.11 The impact of URE has also been assessed by examining summary measures of health loss, using disability-adjusted life years (DALYs). Unlike prevalence rates which depend on definitions of URE, DALYs enable comparisons of broad epidemiologic patterns across time and countries. Recent data from the GBD 2013 study, which included 306 diseases and injuries for 188 countries, revealed that among eye diseases, URE had the greatest burden of 11.3 million DALYs, followed by cataract 2.9 million DALYs.12 Uncorrected refractive error remains to be a major challenge and has been a focus of ophthalmologic research. The aim of this study was to make comparative assessments of the global health burden of URE over time and across age-sex groups, regions, and countries with different socioeconomic status by using the most recent data available from the GBD 2013 study. 
Methods
Global Burden of URE
Uncorrected refractive error refers to refractive errors that could be corrected with spectacles but have not been. Myopia, hyperopia, astigmatism, and presbyopia are the four most common refractive errors. According to the list of the International Classification of Diseases, Tenth Revision (ICD-10) codes for all GBD causes, ICD-10 codes H49-H52 are mapped to URE in the GBD 2013 study.13 Methods to generate DALYs estimates in the GBD 2013 study have been previously described.12 DALYs are calculated as the sum of years lived with disability (YLDs) and years of life lost (YLLs) because of premature death. DALYs estimates for URE were equal to YLDs, according to the GBD 2013 study.12,13 The following data regarding URE burden were extracted from the GBD Data Tool14: (1) global DALYs, DALYs per 100,000 population (controlling for population size), and age-standardized DALYs per 100,000 population (controlling for population size and composition) in 1990, 1995, 2000, 2005, 2010, and 2013, (2) global and national age- and sex-specific DALYs and DALYs per 100,000 population in 2013, (3) World Health Organization (WHO) regional DALYs, DALYs per 100,000 population, and age-standardized DALYs per 100,000 population in 2013, and (4) national age-standardized DALYs per 100,000 population in 2013. 
National Socioeconomic Status
The Human Development Index (HDI) in 2013 was obtained from the United Nations Development Programme (UNDP) database, based on the Human Development Report 2014.15 The HDI is a composite measure of health, education, and income of a country, including four components, namely life expectancy at birth, mean years of schooling, expected years of schooling, and gross national income per capita. The HDI ranges from 0 to 1, with a higher value indicating a higher degree of human development. Using the UNDP categorization, countries were classified into four socioeconomic groups as follows: very high human development (HDI ≥ 0.808), high (0.808 > HDI ≥ 0.700), medium (0.700 > HDI ≥ 0.556), and low (HDI < 0.556). 
Statistical Analysis
Comparisons of sex difference in national DALY numbers and crude DALY rates for each age group were performed by Mann-Whitney U test.16 The differences of age-standardized DALY rates among four HDI-based country groups were explored by Kruskal-Wallis test,17 followed by evaluation for multiple comparisons using Mann-Whitney U test. Linear regression analysis was performed to investigate the effect of national HDI on age-standardized DALY rates. All statistical analyses were performed using SPSS 23 (IBM, Chicago, IL, USA). P values of less than 0.05 were considered statistically significant. 
Results
Global Patterns in URE Burden by Year
Global DALY numbers caused by URE rose by 43.8%, from 7.8 (95% uncertainty interval [UI]: 5.0–12.0) million in 1990 to 11.3 (95% UI: 7.1–17.5) million in 2013 (Fig. 1A). After removing the impact of a growing world population during the same period, DALY rates for URE remained relatively constant, increasing slightly from 147.5 (95% UI: 94.5–225.9) to 157.1 (95% UI: 99.8–243.6) (Fig. 1B). Further controlling for population size and composition changes between 1990 and 2013, shows that, URE burden in terms of age-standardized DALY rates fell by 8.8%, from 185.3 (95% UI: 119.3–282.8) to 169.0 (95% UI: 107.5–261.5) (Fig. 1C). 
Figure 1
 
Trends in global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C), from 1990 to 2013. Shade areas represent 95% uncertainty intervals.
Figure 1
 
Trends in global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C), from 1990 to 2013. Shade areas represent 95% uncertainty intervals.
Global Patterns in URE Burden by Age and Sex
DALY numbers and crude rates by age and sex were available for 188 countries in 2013. Mann-Whitney U test revealed no significant sex difference in national DALY numbers for each age group (P > 0.05). However, globally older females had higher number of DALYs than males of the same age (Fig. 2A). The changes of global DALYs by age were similar in both sexes, remaining relatively constant in the age range of 5 to 40 years and reaching two peaks in the age range of 60 to 65 and greater than or equal to 80 years. Likewise, for each age group no sex difference in national DALY rates was detected by Mann-Whitney U test (P > 0.05). However, global DALY rates were higher in older females than in males of the same age (Fig. 2B). The changes of DALY rates by age were similar in both sexes, increasing slowly under 40 years of age and rapidly above 40 years of age. 
Figure 2
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B) by age and sex in 2013.
Figure 2
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B) by age and sex in 2013.
Global Patterns in URE Burden by Region
Of the 188 countries included in the GBD 2013 study, there are 11 South-East Asian countries, 23 Western Pacific countries, 51 European countries, 34 American countries, 47 African countries, and 22 Eastern Mediterranean countries. The highest number of DALYs was observed in South-East Asia (including India) with 3.9 (95% UI: 2.6–5.8) million, followed by Western Pacific (including China) with 1.9 (95% UI: 1.1–3.0) million in 2013 (Fig. 3A). After controlling for population size, the highest DALY rate was found in South-East Asia (210.0; 95% UI: 141.4–310.6), followed by Eastern Mediterranean (188.7; 95% UI: 125.3–276.9), with the lowest in Western Pacific (100.3; 95% UI: 59.3–163.3) (Fig. 3B). Regional age-standardized DALY rates in Eastern Mediterranean (276.0; 95% UI: 185.8–399.6), South-East Asia (270.3; 95% UI: 182.4–395.2), and Africa (224.8; 95% UI: 145.4–341.9) were higher than global age-standardized DALY rate in 2013 (Fig. 3C). 
Figure 3
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C) by WHO region in 2013. Lines represent 95% uncertainty intervals.
Figure 3
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C) by WHO region in 2013. Lines represent 95% uncertainty intervals.
Global Patterns in URE Burden by Socioeconomic Development
Data of HDI were available for 183 countries which were classified into four socioeconomic groups, including very high (n = 47), high (n = 51), medium (n = 42), and low (n = 43) HDI countries. Kruskal-Wallis tests indicated that age-standardized DALY rates differed significantly among countries with different socioeconomic development levels (χ2(3) = 81.074, P < 0.001). Multiple comparisons using Mann-Whitney U tests revealed higher age-standardized DALY rates in lower HDI countries (Fig. 4A). The medians (interquartile ranges) of age-standardized DALY rates in low, medium, high, and very high HDI countries were 240.9 (196.0–272.9), 197.6 (162.8–245.7), 160.6 (133.2–180.5), and 123.2 (107.9–131.4), respectively. Linear regression analysis indicated that HDI had a significant effect on age-standardized DALY rates (adjusted R2 = 0.376; F(1, 181) = 110.509, P < 0.001). As can be seen in Figure 4B, age-standardized DALY rates were inversely associated with HDI (standardized β = −0.616, P < 0.001). 
Figure 4
 
Global burden of URE in terms of age-standardized DALY rates by national socioeconomic development in 2013. (A) URE burden differed among countries with different socioeconomic development levels. Lines represent the median burden. **P < 0.01, ***P < 0.001. (B) URE burden was inversely related to socioeconomic development level. The line represents a linear fit.
Figure 4
 
Global burden of URE in terms of age-standardized DALY rates by national socioeconomic development in 2013. (A) URE burden differed among countries with different socioeconomic development levels. Lines represent the median burden. **P < 0.01, ***P < 0.001. (B) URE burden was inversely related to socioeconomic development level. The line represents a linear fit.
Discussion
This study revealed the global patterns in health burden of URE by year, age and sex, region, and socioeconomic status. From 1990 to 2013, global DALY numbers rose, crude rates stayed stable, and age-standardized rates declined. Global DALY rates increased with age, and older females had higher DALY numbers and rates than males of the same age. Among six WHO regions, age-standardized DALY rates in Eastern Mediterranean, South-East Asia, and Africa were higher than that at a global level. Higher age-standardized DALY rates were found in countries with lower levels of socioeconomic development. 
Ono et al.18 using data from the GBD 2004 study, reported world bank regional difference, with higher DALYs caused by refractive errors in East Asia and the Pacific (including China), and South Asia (including India), which agrees with our findings. However, we had gone further and found higher URE burden in Eastern Mediterranean, South-East Asia, and Africa, after excluding the impact of population size and composition. Ono et al.18 also reported that refractive errors burden in terms of crude DALY rates were higher in high-income countries than in middle- and low-income countries, which seems inconsistent with our analysis.18 The difference between the terms of crude rates and age-standardized rates should be noted. Besides, the global burden of refractive errors in the GBD 2004 study was probably underestimated, based only on presenting distance visual acuity.19 It has been estimated that 94% (386 million) of people with near-vision impairment due to uncorrected presbyopia lived in developing countries in 2005.20 The World Health Survey conducted in 70 countries worldwide in 2003 reported the percentage of adults suffering from any distant visual difficulty being 13%, 23%, and 24% in high-, middle-, and low- income countries, respectively.21 Like the global patterns in URE burden demonstrated in our study, older age, female sex, as well as lower socioeconomic status, were identified as risk factors for visual difficulty in the World Health Survey.21 
According to the findings of the GBD 2010 study, global number of cases of MSVI and blindness due to URE increased by 15% and 7.9%, respectively, from 1990 to 2010, less than the population growth of 30% during the same period.2 Meanwhile, global age-standardized prevalence of MSVI and blindness due to URE declined by 25% and 33%, respectively.2 The findings might partially explain the trends in global URE burden in terms of DALY numbers, crude rates, and age-standardized rates in the GBD 2013 study. Global health of URE is improving, which could be a consequence of eye-care development by the VISION 2020 program, the International Agency for the Prevention of Blindness, national programs, and nongovernment organizations. However, an increasing and aging population, as well as the transition to a younger onset of URE,22 have raised DALY numbers and kept crude rates stable, implying that health improvement does not mean fewer demands of refractive services. 
Age-specific analysis of the GBD 2010 study revealed that, global age-standardized prevalence of MSVI due to URE among people aged 50 years and older versus in all age was 5.3% vs. 1.5%, and blindness 0.4% vs. 0.1%.2 With an assumed onset age of 40 to 45 years, presbyopia is nearly universal in individuals over 65-years old and is becoming a major contributor to the global burden of VI in old people.20 Recent projections indicate that, the distribution of people with myopia will spread from 2000 with a peak in the age range of 10 to 39 years, by 2050 with a peak throughout the age range of 10 to 79 years.23 The number of people with high myopia globally was 163 million in 2000 and is projected to increase to 938 million by 2050.23 The pathologic changes in high myopia may increase drastically over the next few decades, largely due to the increasing number of high myopia cases and the aging population.24 In 2010, age-standardized prevalence of VI-URE was higher in females than in males in all regions worldwide.2 Sex inequality existed in accessibility to eye care services, with evidence that females do not access eye care as often as males especially in developing countries.25 Greater longevity of females in many countries also contributes to a higher global burden of URE in older females.26 
Among 21 GBD regions, the highest number of people with VI-URE was found in South Asia, followed by East Asia.2 India and China account for approximately 50% of the global VI-URE.2,27 In our analysis, countries with lower HDI have higher age-standardized DALY rates caused by URE. Availability of eye care is a major barrier to correcting refractive errors.28 The average number of eye doctors per million population varied with economic development, from 9 per million in low-income countries to 79 per million in high-income countries, with the lowest average number (2.7 per million) in Sub-Saharan Africa.29 Another notable barrier is the quality of care available. Even in developed countries, refractive errors could be undetected or undercorrected in children.30,31 This could be more challenging for less developed regions, for example, South Asia that has is a relatively younger population2. Moreover, the cost of eye exam and spectacles impedes refractive correction to a great extent in poor regions.3234 For instance, 99.5% of survey participants from Timor-Leste were willing to wear spectacles if needed, whereas the proportion willing to pay at least US$1 was only 56.9%, despite the National Spectacle Program.34 
This study was subject to the limitations of the GBD 2013 study, such as data sources and statistical assumptions, which were detailed in the GBD 2013 reports.12,13 The key limitation is the use of aggregate data for each country rather than district data, as a source of bias because of geographic variations in DALYs of URE. As annual updates of GBD data are available, analysis of global URE burden by age and sex, region, and socioeconomic status over time could be further explored. 
In summary, this study suggests that the global health of URE is improving but an increasing and aging population keeps crude DALY rates stable. Health progress in URE does not mean fewer demands of refractive services. Older people and females worldwide bear higher burden of URE. The association between URE burden with socioeconomic status highlights the need to provide cost-effective refractive services for less developed countries. The findings of this study may raise public awareness of the global URE burden and are important for health policy making. 
Acknowledgments
Supported by grants from Zhejiang Provincial Program for Medical and Health Science Co-sponsored by Province and Ministry (Hangzhou, Zhejiang, China), and Zhejiang Provincial Program for Cultivation of High-Level Innovative Health Talents (Hangzhou, Zhejiang, China). 
Disclosure: L. Lou, None; C. Yao, None; Y. Jin, None; V. Perez, None; J. Ye, None 
References
Bourne RR, Stevens GA, White RA, et al. Causes of vision loss worldwide 1990-2010: a systematic analysis. Lancet Glob Health. 2013; 1: e339–e349.
Naidoo KS, Leasher J, Bourne RR, et al. Global vision impairment and blindness due to uncorrected refractive error, 1990-2010. Optom Vis Sci. 2016; 93: 227–234.
Holden BA. Blindness and poverty: a tragic combination. Clin Exp Optom. 2007; 90: 401–403.
Tahhan N, Papas E, Fricke TR, Frick KD, Holden BA. Utility and uncorrected refractive error. Ophthalmology. 2013; 120: 1736–1744.
Smith TS, Frick KD, Holden BA, Fricke TR, Naidoo KS. Potential lost productivity resulting from the global burden of uncorrected refractive error. Bull World Health Organ. 2009; 87: 431–437.
Fricke TR, Holden BA, Wilson DA, et al. Global cost of correcting vision impairment from uncorrected refractive error. Bull World Health Organ. 2012; 90: 728–738.
Saw SM, Foster PJ, Gazzard G, Friedman D, Hee J, Seah S. Undercorrected refractive error in Singaporean Chinese adults: the Tanjong Pagar survey. Ophthalmology. 2004; 111: 2168–2174.
Rosman M, Wong TY, Tay WT, Tong L, Saw SM. Prevalence and risk factors of undercorrected refractive errors among Singaporean Malay adults: the Singapore Malay Eye Study. Invest Ophthalmol Vis Sci. 2009; 50: 3621–3628.
Varma R, Wang MY, Ying-Lai M, Donofrio J, Azen SP; Group LALES. The prevalence and risk indicators of uncorrected refractive error and unmet refractive need in Latinos: the Los Angeles Latino Eye Study. Invest Ophthalmol Vis Sci. 2008; 49: 5264–5273.
Thiagalingam S, Cumming RG, Mitchell P. Factors associated with undercorrected refractive errors in an older population: the Blue Mountains Eye Study. Br J Ophthalmol. 2002; 86: 1041–1045.
Holden BA. Uncorrected refractive error: the major and most easily avoidable cause of vision loss. Community Eye Health. 2007; 20: 37–39.
Murray CJ, Barber RM, Foreman KJ, et al. Global, regional, and national disability-adjusted life years (DALYs) for 306 diseases and injuries and healthy life expectancy (HALE) for 188 countries, 1990-2013: quantifying the epidemiological transition. Lancet. 2015; 386: 2145–2191.
Vos T, Barber RM, Bell B, et al. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2015; 386: 743–800.
Global Health Data Exchange. GBD Data Tool. Available at: http://ghdx.healthdata.org/gbd-data-tool. Accessed May 1, 2016.
Malik K. Human Development Report 2014. Sustaining Human Progress: Reducing Vulnerabilities and Building Resilience. Tokyo, Japan, July 24, 2014. Available at: http://hdr.undp.org/en/content/human-development-report-2014.
Nachar N. The Mann-Whitney U: a test for assessing whether two independent samples come from the same distribution. Tutor Quant Methods Psychol. 2008; 4: 13–20.
Chan Y, Walmsley RP. Learning and understanding the Kruskal-Wallis one-way analysis-of-variance-by-ranks test for differences among three or more independent groups. Phys Ther. 1997; 77: 1755–1762.
Ono K, Hiratsuka Y, Murakami A. Global inequality in eye health: country-level analysis from the Global Burden of Disease Study. Am J Public Health. 2010; 100: 1784–1788.
Mathers C, Fat DM, Boerma JT. World Health Organization. The Global Burden of Disease: 2004 Update. Geneva, Switzerland, 2004. Available at: http://www.who.int/healthinfo/global_burden_disease/2004_report_update/en/.
Holden BA, Fricke TR, Ho SM, et al. Global vision impairment due to uncorrected presbyopia. Arch Ophthalmol. 2008; 126: 1731–1739.
Freeman EE, Roy-Gagnon MH, Samson E, et al. The global burden of visual difficulty in low, middle, and high income countries. PLoS One. 2013; 8: e63315.
Holden B, Sankaridurg P, Smith E, Aller T, Jong M, He M. Myopia, an underrated global challenge to vision: where the current data takes us on myopia control. Eye. 2014; 28: 142–146.
Holden BA, Fricke TR, Wilson DA, et al. Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology. 2016; 123: 1036–1042.
Verkicharla PK, Ohno-Matsui K, Saw SM. Current and predicted demographics of high myopia and an update of its associated pathological changes. Ophthalmic Physiol Opt. 2015; 35: 465–475.
Courtright P, Lewallen S. Improving gender equity in eye care: advocating for the needs of women. Community Eye Health. 2007; 20: 68–69.
Regan JC, Partridge L. Gender and longevity: why do men die earlier than women? Comparative and experimental evidence. Best Pract Res Clin Endocrinol Metab. 2013; 27: 467–479.
Pascolini D, Mariotti SP. Global estimates of visual impairment: 2010. Br J Ophthalmol. 2012; 96: 614–618.
Durr NJ, Dave SR, Lage E, Marcos S, Thorn F, Lim D. From unseen to seen: tackling the global burden of uncorrected refractive errors. Annu Rev Biomed Eng. 2014; 16: 131–153.
Resnikoff S, Felch W, Gauthier TM, Spivey B. The number of ophthalmologists in practice and training worldwide: a growing gap despite more than 200,000 practitioners. Br J Ophthalmol. 2012; 96: 783–787.
O'Donoghue L, Rudnicka AR, McClelland JF, Logan NS, Saunders KJ. Visual acuity measures do not reliably detect childhood refractive error-an epidemiological study. PLoS One. 2012; 7: e34441.
Qiu M, Wang SY, Singh K, Lin SC. Racial disparities in uncorrected and undercorrected refractive error in the United States. Invest Ophthalmol Vis Sci. 2014; 55: 6996–7005.
Thompson S, Naidoo K, Gonzalez-Alvarez C, Harris G, Chinanayi F, Loughman J. Barriers to use of refractive services in Mozambique. Optom Vis Sci. 2015; 92: 59–69.
Marmamula S, Keeffe JE, Raman U, Rao GN. Population-based cross-sectional study of barriers to utilisation of refraction services in South India: Rapid Assessment of Refractive Errors (RARE) Study. BMJ Open. 2011; 1: e000172.
Ramke J, Brian G, Naduvilath T. Refractive error and presbyopia in Timor-Leste: the impact of 5 years of a national spectacle program. Invest Ophthalmol Vis Sci. 2012; 53: 434–439.
Figure 1
 
Trends in global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C), from 1990 to 2013. Shade areas represent 95% uncertainty intervals.
Figure 1
 
Trends in global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C), from 1990 to 2013. Shade areas represent 95% uncertainty intervals.
Figure 2
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B) by age and sex in 2013.
Figure 2
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B) by age and sex in 2013.
Figure 3
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C) by WHO region in 2013. Lines represent 95% uncertainty intervals.
Figure 3
 
Global burden of uncorrected refractive errors in terms of DALY numbers (A), crude DALY rates (B), and age-standardized DALY rates (C) by WHO region in 2013. Lines represent 95% uncertainty intervals.
Figure 4
 
Global burden of URE in terms of age-standardized DALY rates by national socioeconomic development in 2013. (A) URE burden differed among countries with different socioeconomic development levels. Lines represent the median burden. **P < 0.01, ***P < 0.001. (B) URE burden was inversely related to socioeconomic development level. The line represents a linear fit.
Figure 4
 
Global burden of URE in terms of age-standardized DALY rates by national socioeconomic development in 2013. (A) URE burden differed among countries with different socioeconomic development levels. Lines represent the median burden. **P < 0.01, ***P < 0.001. (B) URE burden was inversely related to socioeconomic development level. The line represents a linear fit.
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×