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HomemifeatureMyopia: A 21st Century Public Health Issue

Myopia: A 21st Century Public Health Issue

The global prevalence of myopia and high myopia is rapidly increasing, largely due to modern urban lifestyles. While there may be little we can do to change our lifestyle, it may be possible to prevent or delay the onset of myopia and slow its progression in those who are myopic.

The world’s urban population is growing, with the number of people living in cities and so-called megacities (population over 10 million) steadily on the rise.

In the year 2016, our world had 31 megacities and an estimated 55 per cent of the world’s population lived in urban settlements.1 It is expected that by the year 2030, there will be 41 megacities and nearly 60 per cent of the world’s population will live in urban settlements. As hubs that drive commerce, trade and innovation, these cities are also home to nearly half of the children of the world.2

For many children, life in an urban community is dominated by high density living and small living areas. As a consequence, time spent outdoors is restricted and in some instances, penetration of natural light to indoor spaces is limited (Figure 1). Furthermore, a pursuit of academic achievement in certain societies and countries means that on any given day, children will spend an inordinately long time on near based activities, such as reading and writing. Additionally, recent technological advances, with respect to smart phone and screen based devices, has resulted in many children spending a significant amount of time focussed on near range activities.

21st century living, dominated by increased exposure to near based activities and a reduced exposure to outdoor time… is linked to the current worldwide epidemic of myopia

It is clear that 21st century living, dominated by increased exposure to near based activities and a reduced exposure to outdoor time, poses a challenge to the health of the young growing eye and is linked to the current worldwide epidemic of myopia. The causal role of living conditions in the epidemic is demonstrated through studies that show myopia is more prevalent in urban compared to rural areas, as well as studies that suggest environmental exposure to risk factors is more significant than genetic factors in the onset and progression of myopia.3-7 Additionally, there is a large and growing body of evidence supporting the role that limited outdoor and/or excessive indoor/near work activity plays in the development of myopia.

An Increasingly Myopic World

A systematic review and meta-analysis of literature on myopia prevalence from 1995 to 2015 found that in the year 2000, approximately 23 per cent of the world’s population was myopic. This figure was estimated to rise significantly to affect nearly 50 per cent of the global population by the year 20508 (Figure 2). While this estimated prevalence of myopia is alarming, already, the prevalence of myopia is extremely high in children in many Asian countries.

Children in Taiwan have the highest prevalence of myopia recorded anywhere, with myopia prevalence showing a steady increase from 1983 to 2000; ranging from six to 20 per cent in children aged seven years and increasing to nearly 80 per cent in children aged 16 to 18 years.9 In Japan, prevalence of myopia was observed to increase from approximately 49 per cent to nearly 66 per cent in 17 year olds during a 13 year period from 1984 to 1996.10 In two population based cross-sectional surveys conducted in urban and rural China, prevalence of myopia in urban based children aged seven years was 7.7 per cent and 15 years was 78.4 per cent. Prevalence in rural China was slightly lower at 43 per cent in 15 year olds.3,4 In Hong Kong, prevalence rates of myopia (using non-cycloplegia) in school children aged six and 12 years were 18.5 per cent and 61.5 per cent respectively.11 Although the prevalence is lower in non-Asian populations, increasing levels of myopia have been documented elsewhere in the world. Based on 13 studies and nearly 60,000 participants, the E3 European Consortium reported prevalence of myopia for those completing primary, secondary and higher education to be 25.4 per cent, 19.1 per cent and 36.6 per cent, and reported a trend of higher myopia prevalence with more recent birth decades across all age groups.12

As a consequence of this rise in the prevalence of myopia, prevalence of high myopia (–5.00 D or worse) is also on the rise. From a prevalence of 2 per cent in 2000, it is estimated that the prevalence of high myopia will reach 9.5 per cent by the year 2050. Notably, the prevalence of high myopia is expected to increase at a more rapid rate compared to the overall prevalence of myopia, especially in Asia Pacific countries. One possible explanation for this disproportionate increase in high myopia could be related to an earlier onset of myopia than before. Evidence exists for myopia occurring in a significant proportion of children at commencement of school age (age five to six years) or even younger. Prevalence of myopia in three and four year olds was 1.8 per cent and 2.3 per cent in a cross-sectional study conducted in Shanghai, China; 6.3 per cent in Hong Kong preschools; and 13.2 per cent in children aged five to six in Korea.13-15

An earlier onset in myopia results in the eye reaching high levels of net myopia as:

a ) myopia is likely to progress for a longer duration compared to an eye with a later onset myopia; and

b) younger ages are associated with substantially greater annual progression in comparison to older ages.16

The Rising Burden of Myopia

The already high prevalence of myopia in parts of Asia, as well as trends towards a further increase in the number of eyes reaching myopia and high myopia respectively, have created a significant social, economic and health challenge.

For some, myopia is simply an inconvenience that needs correction with optical devices such as spectacles or contact lenses. The inconvenience is not without cost as myopia is commonly progressive during childhood, requiring regular eye examinations and appropriate management.

The services required to manage the burden are significant and include the direct costs of goods and services such as eye exams and optical devices; and indirect costs to the individual, carers and society such as development and management of human resources to manage the burden.

More importantly, increasing levels of myopia, particularly at moderate to high levels, and especially later in adult life, increase the risk of the eye developing a number of serious and sight-threatening complications and sequelae. Even in younger individuals, moderate to high levels of myopia increase the risk of paediatric retinal detachment and other peripheral retinal conditions. Indeed, myopia is one of the leading causes of paediatric retinal detachment especially in Asian countries.17-19

Myopia in older individuals predisposes the eye to developing vision impairment and complications such as glaucoma, retinal detachment and myopic maculopathy; and much of the vision loss associated with these complications is irreversible. In a study of nearly 15,000 individuals, prevalence of visual impairment rose with increasing axial length of 26mm or greater and spherical equivalent of -6.00D or worse. Vision impairment was found in 5.7 per cent of participants aged 60 years and increased to 39 per cent in those aged 75-years with myopia of -6.00D or worse.20 Myopia is thought to increase the risk of glaucoma,21,22 and increasing axial length was found to increase the risk of developing glaucomatous optic neuropathy.23,24 In a retrospective hospital based study involving 519 highly myopic patients, prevalence of glaucomatous optic neuropathy was 28 per cent and increased with increasing axial length.24 Furthermore, eyes with high myopia were often at risk of developing degenerative changes in the chorio-retinal layers, leading to functional loss of vision. Myopic retinopathy was found to increase significantly with increasing myopic refractive error from 3.8 per cent in eyes with myopia of -4.00D or worse to nearly 90 per cent in those with myopia of at least -10.00D.25 The more progressive and degenerative form of myopic maculopathy known as ‘myopic macular degeneration’ is now a leading cause of blindness and vision impairment in many parts of the world.26-28

The Way Forward

A multitude of factors associated with increasing urbanisation – limited time outdoors, an over emphasis on educational pursuits and technological advances that result in excessive time on screen based devices – have created a maelstrom of rising levels of myopia worldwide.

Consideration for managing the condition includes the direct cost this burden will have on individuals, health services and communities, and the indirect costs to the economy due to lost productivity.

Addressing the burden with appropriate strategies involves:

a) acknowledgement and recognition of the issue;

b) broad based collaboration between policy makers, communities and governments to acknowledge the burden of myopia and ensure effective implementation of policies in schools, community and other channels; and

c) development of appropriate intervention strategies.

In 2017, the World Health Organisation released a report on the impact of myopia and high myopia based on the Joint World Health Organization and Brien Holden Vision Institute Global Scientific Meeting on Myopia conducted in 2015. The report acknowledges and recognises the issue and suggests that acquisition of data to inform clinical practice and public health policy should be considered a priority.29

In this respect, we have accumulated evidence to show that while there may be little that we can do to change our lifestyle, it may be possible to prevent or delay the onset of myopia and also slow the progression in those who are myopic. Improving time outdoors for children, especially young children of primary school age, may directly impact on the high prevalence of myopia. Additionally, there are a number of optical and pharmaceutical based treatments available that can slow progression for individuals who already present with myopia.

A shared vision across the various groups – researchers, clinicians, individuals, carers, community and governments – to manage the burden with timely and effective interventions, will improve the eye health of our children and reduce the burden of myopia.

Professor Padmaja Sankaridurg is the myopia program leader and Intellectual property manager at Brien Holden Vision Institute. She is also conjoint professor at the University of New South Wales, School of Optometry and Vision Science.

Dr. Monica Jong is the executive manager of science and business projects at Brien Holden Vision Institute and a Visiting Fellow at the University of New South Wales School of Optometry and Vision Science.

References
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