Sight and Sunlight: Reducing Myopia with Sensible Outdoor Time

What’s Driving Increases in Myopia?

The rise in myopia prevalence over the past 70 years can be attributed to three intertwined lifestyles factors:

1)  Less time spent outdoors,

2)  More time spent on near work (reading books, looking at computer screens), and

3)  More intense and prolonged education.

Of these, time outdoors is the most amenable to intervention and the only behavioural factor that has been successfully altered to prevent myopia. Randomised controlled trials, all of which were conducted in China, have shown that increasing the amount of time children spend outdoors prevents myopia onset and progression.⁶ Interestingly, a recent Shanghai study found that continuous periods of at least 15 minutes in bright sunlight were needed to prevent myopic shifts in refractive error over a one-year period.⁷ This finding is somewhat reassuring in that it suggests intermittent, relatively short periods of at least 15 minutes outdoors in sunlight are likely to be beneficial.

Why Does Outdoor Time Prevent Myopia?

The entire and precise mechanisms of the relationship between outdoor time and myopia are yet to be understood. There is strong evidence for a role of the light-dopamine pathway such that the bright sunlight, which can be between 10 and 1,000 times brighter than indoor lighting, leads to release of dopamine in the retina and inhibition of axial eye growth.⁸

There is a wealth of research currently underway into other mechanisms that could contribute to the outdoor-myopia relationship. Promising areas include how the eye detects and uses the wavelength spectrum of visible light, visual contrast, spatial frequency, and ON-OFF pathway activation to regulate eye growth.^9,10 All of these pathways rely on visible light, which seems to be the key visual input involved in regulating eye growth.⁹ Ultraviolet radiation (UVR), therefore, does not appear to be an important factor.

Downsides of Increased Outdoor Time

In Australia, we must be acutely aware that spending time outdoors comes with risks associated with UVR exposure. While we enjoy relatively low rates of myopia (~25% at age 20 years),¹¹ Australia and New Zealand have the highest rates of melanoma in the world and non-melanoma skin cancers are so common in Australia we don’t routinely count them.¹² Australians also have high rates of UVR-related eye disease. We found over 8% of Australians living in Western Australia, predominantly Perth, have or have had a pterygium¹³ and anterior segment cancers, such as ocular surface squamous neoplasia and melanoma of the conjunctiva or ciliary body, are linked to higher past UVR exposure.^14,15

Striking a Balance to Optimise Health

Given our nation’s already high burden of UVR-related eye diseases, it is imperative we take a thoughtful approach when recommending behavioural changes to prevent myopia. One could argue that only recommending more outdoor time to children with myopia is a self-selecting intervention; that is, myopic children already spend less time outside so are at lower risk of UVR-related diseases. Indeed, in the Busselton Healthy Ageing Study, we found that people who had skin cancer had half the rate of myopia compared to those without skin cancer (11% vs 22%) and, in the population more broadly, there is an apparent inverse correlation between the estimated myopia prevalence and pterygium surgery rates or cutaneous melanoma incidence (among those aged <50 years) (Figure 1).¹⁸ However, low-risk is not no-risk. Furthermore, an increasing focus on outdoor interventions to prevent myopia onset19 will, by necessity, mean increasing outdoor time for children who may never develop myopia but could be at risk of UVR-related diseases such as skin cancer.

Figure 1. Temporal changes in the annual incidence of cutaneous melanoma, rates of pterygium excision (private only) and prevalence of myopia. Pterygium excisions and melanoma in younger age groups are decreasing while myopia is increasing. Melanoma and pterygium excision data are crude rates and data are taken from the Australian Institute of Health and Welfare¹⁶ and Medicare Item Reports (item number 42686), respectively. Estimated myopia prevalence is from Holden et al.¹⁷

As UVR is very probably not involved in the myopia-outdoor pathway, we can achieve the benefits of outdoor time without the harms by combining outdoor time with sun-safety practices. The easiest way to limit UVR exposure when outdoors is to avoid going out in the middle of the day. We have extracted measurements of UVR – not accounting for cloud cover and other mitigating factors – from Brisbane, Perth, and Hobart and show in Figure 2 that there is consistently a two- to three-hour period before and after school in which the UVR index is <3 (sun protection is recommended when UV index ≥3²⁰). While time outside is safest when the UV index is below three, outdoor time when the UV index is three or above is still possible, but care should be taken to use sun protection including clothing, sunscreen, hats, and sunglasses.²⁰ Furthermore, in winter, the UV index is <3 for 20 weeks in Hobart and 5.5 weeks in Perth, meaning spending time outdoors any time of day is consistent with sun safety. In Brisbane, however, sun protection during the middle of the day is recommended year-round (Figure 2).

Figure 2. Graphs showing the average UV rating in Brisbane (top), Perth (middle), and Hobart (bottom) at the summer solstice (left), autumn equinox (middle), and winter solstice (right). The blue shaded area indicates times when the UV index is <3 or lower and the corresponding length of daylight hours with UV index <3 is also shown.

Interestingly, increased outdoor time in the middle of winter may be exactly when it is needed most. There is a well-recognised seasonal pattern of axial eye growth among children with myopia such that eye growth and myopia progression is faster in late winter/early spring and slowest in late summer/early autumn (Figure 3). Thus, increasing outdoor time in winter, when eye growth and myopia progression is naturally faster, may be the most effective time for intervention and has the added benefit of a naturally low risk of excessive UVR exposure.

Figure 3. Rates of axial eye growth of WA-ATOM participants over two years showing myopic eye growth is fastest in winter. Blue line: Lowess-smoothed mean, red line: cosine fit.

How Do We Safely Increase Outdoor Time?

Public Health Interventions

In Singapore, Taiwan, and China, where the lifetime risk of myopia in today’s children is very high, public health campaigns have been a key component in addressing rising myopia rates. National interventions aimed at increasing outdoor time have recently led to a drop in rates of school myopia in China²¹ and Taiwan.²² Since 2010, the Taiwanese program Tian-Tian120 has encouraged schools to have students outdoors for 120 minutes each day for myopia prevention.²² Within two years, this program had reversed the trend of myopia, which continues to decrease by -2.3% annually. The Chinese and Taiwanese programs have both incorporated school-supervised outdoor time; however, in Singapore, compulsory outdoor time during school was not acceptable to stakeholders, hence much of the burden of increasing children’s outdoor time has fallen on parents and carers.²³ In Australia, we think it is likely that the burden of altering children’s behaviour is likely to fall on parents and carers. Anecdotally, teachers report having too little time and resources to implement extra outdoor time. Additionally, school hours coincide with the parts of the day with highest UV index, thus creating an extra challenge to safely increasing outdoor time. On the other hand, parents and children alike report difficulties in finding time to go outdoors among existing school and extra-curricular commitments.

Targeted Interventions

With the much lower lifetime risk of myopia in Australia, the population benefits of a public health campaign are lower compared with the rest of Asia. This may mean a more targeted approach to myopia prevention is needed. As outlined in an another article in this issue, there is an increasing focus on prevention of myopia, which requires identifying children at high risk of myopia. We know that children at risk of myopia have lower amounts of hyperopia, longer axial lengths, and faster eye growth than their peers. Thus, there are opportunities to identify children at high risk, but more work in understanding normal eye growth and refractive development is needed to produce tests that are scalable and adequately sensitive.

Once a child at high risk of myopia has been identified, behavioural interventions could be applied by their eye care provider. For example, the World Health Organization has developed the myopia messaging library,²⁴ a messaging template that is designed to initiate behaviour change through regular delivery of select messages to recipients via an app or SMS. A formal behavioural intervention such as this should be empirically validated; it is not enough to tell a child to spend more time outdoors, it must be shown that the intervention can actually alter behaviour.

Eye Care Practitioner’s Role in Behavioural Change

While currently there is no established clinical intervention to increase outdoor time for management of myopia, advising parents and children on the importance of outdoor time for eye health should form an integral component in the management of myopia. Such recommendations are included in the RANZCO Position statement on progressive myopia in children, but missing from the recent Optometry Australia Position statement on myopia management25 and should be included in future revisions. It is the responsibility of all eye care practitioners to encourage outdoor behaviours for children that both lead to benefits in terms of preventing onset of myopia or limiting its progression, as well as limit potential harms associated with UVR exposure. Practical recommendations for parents and children include:

• Aim for two hours outdoors daily. This doesn’t have to be consecutive; outdoor periods of at least 15 minutes during daylight hours can be beneficial for preventing myopia onset and progression.
• Going outdoors in the morning and evening (when UV index <3) is safest. Download the SunSmart app (available at sunsmart.com.au) to check the UV index for your location and time of year.
• While physical activity is not essential to achieve myopia benefits; outdoor sports, particularly organised sports before and after school and during the winter months, are a great way to ensure outdoor time and come with additional health benefits. The Australian Sports Commission lists the most popular sports undertaken by children: football (Australian Rules, soccer, and rugby), athletics, tennis, cricket, and hockey are usually played outdoors while basketball, gymnastics, swimming, dance, and netball can be done outdoors.²⁶
• If going outside when the UV index is ≥3, use full sun protection, including hats and sunglasses (which do not substantially reduce the benefits obtained from outdoor time). For children with deeply pigmented skin, that rarely or never burns, sunscreen may not be needed for short outdoor periods, but a hat and sunglasses should still be used.²⁰
• Encourage families to integrate outdoor time into their daily lives: walk to school, do homework or read books outside (easier using paper vs computer screens), eat a meal outdoors. Aiming to make outdoor space at the home comfortable and child-friendly may also help.

Of course, outdoor time for families living in apartments is significantly more challenging, with higher density living linked to a higher prevalence of myopia. Very low availability of green space has been linked to higher rates of myopia,²⁷ and the eye care profession should be aiming to ensure urban planners are aware of the benefits of green space on eye health, alongside other health benefits.

Time to Promote Change

Ultimately, more hard data is needed to improve our understanding of how we, as eye care practitioners, can optimally integrate behavioural interventions into myopia care. However, increasing outdoor time is a cheap and effective method for managing myopia that also comes with additional health benefits such as increased physical activity and its knock-on effects. We should, therefore, be recommending children and adolescents spend enough time outdoors to reap eye and health benefits while also undertaking sun safe practices to minimise risks. Expanding our role within the broader health care space to promote behaviour change and policy initiatives ensures the best health outcomes for today’s young Australians.

Professor David Mackey AO MBBS MD FRANZCO FRACS FAHMS FARVO is an internationally renowned clinician, scientist, and academic. He is Professor of Ophthalmology at the University of Western Australia and was the Lions Eye Institute’s Managing Director from 2009 until 2018.

Dr Gareth Lingham MOrth PhD is a Postdoctoral Research Fellow at the Lions Eye Institute, a Clinical Data Analyst with Ocumetra, and holds adjunct positions with Technological University Dublin and the Centre for Eye Research Australia.

Timothy Lewis-Carroll is a Research Assistant at the Lions Eye Institute.

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