The epidemics of myopia: Aetiology and prevention
Introduction
As a recent report in Nature, entitled “The Myopia Boom” demonstrated, it is now widely accepted that there is an epidemic of myopia in the developed countries of East and Southeast Asia, paralleled by an epidemic of high myopia (Dolgin, 2015). Recent meta-analyses have suggested that close to half of the world's population may be myopic by 2050, with as much as 10% highly myopic (Holden et al., 2016a). Because of the links of high myopia to pathological myopia (Spaide et al., 2014), in which changes in the choroid, retina and sclera can lead to uncorrectable vision loss, and because correction of the underlying refractive error does not prevent the appearance of pathology, prevention of myopia and particularly high myopia has become an important international public health priority (Morgan et al., 2012, Holden et al., 2016b).
These epidemics have been extensively reviewed from a variety of perspectives (Foster and Jiang, 2014, French et al., 2013a, Holden et al., 2014, Holden et al., 2016a, Holden et al., 2016b, Hysi et al., 2014, Morgan, 2003, Morgan and Rose, 2005, Morgan and Rose, 2013, Morgan et al., 2012, Ohno-Matsui et al., 2016, Pan et al., 2012, Rose et al., 2016, Sankaridurg and Holden, 2014, Wallman and Winawer, 2004, Wojciechowski, 2011, Wojciechowski and Hysi, 2013), which can be consulted for more details. The specific aim of this review is to bring together the evidence that there is an epidemic of myopia in the developed countries of East and Southeast Asia, to compare it to an epidemic of myopia in Jewish boys attending Orthodox schools in Israel, to analyse the conditions in which the epidemics of myopia have emerged, and to link broad changes in society to specific changes in education and specific environmental exposures such as near work and time outdoors, through to biological pathways. We will not deal extensively with genetic factors, because it is now generally accepted that genetic change is too slow to explain the rapid changes in prevalence that have taken place in East and Southeast Asia (Hysi et al., 2014, Morgan and Rose, 2005, Wojciechowski, 2011, Wojciechowski and Hysi, 2013). For the purpose of this review, we will simply note that genetic factors impose a level of baseline risk of myopia, and concentrate on the associations of myopia with environmental risk factors which have led to the epidemic of myopia in the developed countries of East and Southeast Asia. We conclude that changes in education and the time that children spend outdoors have played a major causal role in the emergence of the myopia epidemics, and that these factors can be modified to achieve prevention.
Section snippets
The evidence for an epidemic
In the developed countries of East and Southeast Asia, the prevalence of myopia is now 80–90% in children completing secondary schooling at the age of 17–18 (Morgan et al., 2012), compared to the prevalences of 20–40% seen in many developed western countries (Cumberland et al., 2015, Morgan et al., 2012, Pan et al., 2012, Vitale et al., 2008, Vitale et al., 2009, Williams et al., 2015a). In contrast, in less developed parts of the world, with less developed education systems, the prevalence of
The evidence for an epidemic of high myopia
In parallel with the epidemic of school myopia, an epidemic of high myopia (more than 5 or 6D of myopia) has appeared. This epidemic was clear in the first studies from Taiwan (Ding et al., 2017, Lin et al., 2004). Fig. 3 shows current data on myopia and high myopia from East and Southeast Asia. The prevalence of high myopia has increased by as much as 10-fold, more than the proportional increase in total myopia, meaning that the percentage of myopes who become highly myopic has increased (
Comparison with societies with little formal education
There are few studies with good methodology in societies with little formal education, but the prevalence of myopia, determined with cycloplegia, was only 0.4% in a large sample of illiterate African adults in Gabon (Holm, 1937), and the prevalence of myopia under cycloplegia in uneducated adult Inuit was only 1.2% (Skeller, 1954). Only 20 years later, several papers using cycloplegia reported low prevalences of myopia in older Inuit, with much higher prevalences in the younger adults (Alsbirk,
Environmental risk factors
While the systematic association of myopia prevalence with educational experiences is striking, as with all associations, it could be confounded by parallel changes. As societies have developed, there have been systematic increases in education, but there have been parallel changes in a number of other parameters such as family income, living environments, including changes in population density, style of housing, pollution, diet, and lifestyle, and some associations with factors of this kind
Time outdoors as a protective factor
There is now consistent evidence that children who spend more time outdoors are less likely to be or become myopic (Dirani et al., 2009, French et al., 2013a, French et al., 2013b, Guggenheim et al., 2012, Guo et al., 2013a, Guo et al., 2013b, He et al., 2015, Ip et al., 2008, Jones et al., 2007, Jones-Jordan et al., 2011, Jones-Jordan et al., 2012, Khader et al., 2006, Lin et al., 2014, Mutti et al., 2002, Onal et al., 2007, Parssinen and Lyyra, 1993, Rose et al., 2008a, Rose et al., 2008b,
Time outdoors
Studies on animal models have shown that, at least in the form-deprivation model, bright light exposures can completely abolish the development of experimental myopia (Ashby et al., 2009, Ashby and Schaeffel, 2010, Karouta and Ashby, 2015, Lan et al., 2013, Lan et al., 2014, Lan et al., 2016, Norton, 2016, Smith et al., 2012, Smith et al., 2013). It now also generally accepted that the mechanism initially proposed (Rose et al., 2008a), involving light-induced release of dopamine (Boelen et al.,
Time outdoors does not appear to regulate progression
While the biological pathways that lead to delay in the onset of myopia seem to be reasonably clear, there is general agreement that there is little evidence for regulation of progression, defined as myopic shifts in refraction in those who are already myopic (French et al., 2013a, French et al., 2013b, He et al., 2015, Jones et al., 2007, Jones-Jordan et al., 2012, Rose et al., 2008a, Wu et al., 2013a, Wu et al., 2013b, Xiong et al., 2017). However, Parssinen et al. (2014) have reported that
Are genetic differences important?
The tight geographical localization of the myopia epidemic has led to the plausible hypothesis that the populations of these regions might be genetically more susceptible to environmental risk factors than other populations. However, when dealing with ethnic differences, it is vital to consider cultural factors as explanations, because human ethic/racial groups are rather similar in overall genetic terms, while differentiation in terms of cultural factors, while difficult to quantify, is often
A framework for myopia prevention
Seet et al. (2001) developed a framework for understanding the emergence of an epidemic of myopia in Singapore, and for prevention of myopia. They distinguished between distal factors which covered broad social factors such as urbanization and meritocracy, intermediate factors such as indoor environment and near work activity and proximal factors such as genetics and biology. With the advantage of over 15 additional years of research, we propose a more developed hierarchy of causal factors,
Future directions
At one level, future directions in this area are dominated by the need to take action. At the public health level, school-based interventions to increase the amount of time that children spend outdoors provide an immediate approach to reducing the onset of myopia, which should flow through to reductions in the prevalence of high myopia. There is a further need to explore changes to curriculum and school systems to reduce educational pressures, so that more time outdoors is available. Further
Conclusions
Overall, we conclude that the increasing prevalences of myopia and high myopia can be largely explained by two causal factors, increased educational pressures and reductions in the amount of time that children spend outdoors, both of which promote the development of myopia. Increases in the prevalence of myopia can be traced back to the emergence of modern western education systems over 100 years ago. A perfect storm of high educational pressures and limited time outdoors has converged to
Acknowledgements
This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors. The authors have no conflicts of interest to declare.
References (186)
- et al.
Prevalence and risk factors for myopic retinopathy in a Japanese population: the Hisayama Study
Ophthalmology
(2012) - et al.
Exceptionally low prevalence of refractive error and visual impairment in schoolchildren from Lao People's Democratic Republic
Ophthalmology
(2012) - et al.
Five-year clinical trial on atropine for the treatment of myopia 2: myopia control with atropine 0.01% Eyedrops
Ophthalmology
(2016) - et al.
Effect of day length on eye growth, myopia progression, and change of corneal power in myopic children
Ophthalmology
(2013) - et al.
Myopia among school children in East Asia and Singapore
Surv. Ophthalmol.
(2017) The complex interactions of retinal, optical and environmental factors in myopia aetiology
Prog. Ret. Eye Res.
(2012)- et al.
Time outdoors and the prevention of myopia
Exp. Eye Res.
(2013) - et al.
Prevalence and 5- to 6-year incidence and progression of myopia and hyperopia in Australian schoolchildren
Ophthalmology
(2013) - et al.
Risk factors for incident myopia in Australian schoolchildren: the Sydney adolescent vascular and eye study
Ophthalmology
(2013) - et al.
Refractive error and visual impairment in school-age children in Gombak District, Malaysia
Ophthalmology
(2005)
Outdoor activity and myopia among primary students in rural and urban regions of Beijing
Ophthalmology
Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050
Ophthalmology
Efficacy comparison of 16 interventions for myopia control in children: a network meta-analysis
Ophthalmology
Crystalline lens and refractive development
Prog. Retin. Eye Res.
Changes in dopamine and ZENK during suppression of myopia in chicks by intense illuminance
Exp. Eye Res.
Refractive errors in a rural Chinese adult population the Handan eye study
Ophthalmology
Prevalence and progression of myopic retinopathy in Chinese adults: the Beijing Eye Study
Ophthalmology
Prevalence of myopia and refractive changes in students from 3 to 17 years of age
Surv. Ophthalmol.
Refractive error study in children: results from La Florida, Chile
Am. J. Ophthalmol.
Dopaminergic agents affect the ability of brief periods of normal vision to prevent form-deprivation myopia
Exp. Eye Res.
Diurnal patterns of dopamine release in chicken retina
Neurochem. Int.
Myopia and level of education: results from the Gutenberg health study
Ophthalmology
Refraction in adult West Greenland Eskimos. A population study of spherical refractive errors, including oculometric and familial correlations
Acta Ophthalmol.
Quantifying light exposure patterns in young adults
J. Mod. Opt.
Prevalence of refractive errors in school-age children in Morocco
Clin. Exp. Ophthalmol.
The effect of ambient illuminance on the development of deprivation myopia in chicks
Invest. Ophthalmol. Vis. Sci.
The effect of bright light on lens compensation in chicks
Invest. Ophthalmol. Vis. Sci.
Education and myopia in 110,236 young Singaporean males
Singap. Med. J.
Race, culture and Myopia in 110,236 young Singaporean males
Singap. Med. J.
Light-stimulated release of dopamine from the primate retina is blocked by 1-2-amino-4-phosphonobutyric acid (APB)
Vis. Neurosci.
In search of fewer independent risk factors
Arch. Intern. Med.
Myopia prevalence in Chinese-Canadian children in an optometric practice
Optom. Vis. Sci.
The pattern of myopia in young Singaporean men
Singap. Med. J.
Age of onset f myopia predicts risk of high myopia in later childhood in myopic Singapore children
Ophthalmic Physiol. Opt.
Frequency and distribution of refractive error in adult life: methodology and findings of the UK Biobank Study
PLoS One
Prevalence of myopia and hyperopia in a population of Polish schoolchildren
Ophthalmic Physiol. Opt.
Refractive errors in an urban population in southern India: the Andhra Pradesh eye disease study
Invest. Ophthalmol. Vis. Sci.
Population-based assessment of refractive error in India: the Andhra Pradesh eye disease study
Clin. Exp. Ophthalmol.
Refractive error in children in a rural population in India
Invest. Ophthalmol. Vis. Sci.
Children's refractions and visual activities in the school year and summer
Optom. Vis. Sci.
Comparison of measurements of time outdoors and light levels as risk factors for myopia in young Singapore children
Eye
Outdoor activity and myopia in Singapore teenage children
Br. J. Ophthalmol.
The myopia boom
Nature
Myopia progression in Chinese children is slower in summer than in winter
Optom. Vis. Sci.
Myopia progression rates in urban children wearing single-vision spectacles
Optom. Vis. Sci.
Epidemiology of myopia
Eye
Patterns of myopigenic activities with age, gender and ethnicity in Sydney schoolchildren
Ophthalmic Physiol. Opt.
Refractive error in school children in an urban and rural setting in Cambodia
Ophthalmic Epidemiol.
Changes in refractive trends and optical components of Hong Kong Chinese aged 19-39 years
Ophthalmic Physiol. Opt.
Time outdoors and physical activity as predictors of incident myopia in childhood: a prospective cohort study
Invest. Ophthalmol. Vis. Sci.
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