Nearsightedness and Nature-Deficit Disorder

Will kids read this eye chart better if they spend more time outdoors?

Will kids read this eye chart better if they spend more time outdoors?

Why are 80% of kids in Singapore nearsighted? Perhaps it’s a nature-deficit disorder. 

Singapore has one of the highest rates of nearsightedness or myopia in the world, and parts of China and Taiwan are not far behind.

Most people assume it’s just genetics. 

There’s certainly a lot of evidence suggesting a genetic link. In Australia, for example, if both parents have myopia, a child is eight times as likely to have it as well, and if both parents have severe myopia (at least -6 diopter), a child is 22 times as likely (Ip et al. 2007).

People of Chinese origins are particularly prone to myopia (Pan et al. 2012).

But here’s the Singapore twist. The city-state is a melting pot of Chinese, Indian and Malay ethnicities. Yet Singapore has a far higher myopia prevalence rate than India or Malaysia and a slightly higher rate than China.

Genetics almost certainly plays a role in myopia, but families generally share not only genes but also environments.

While our genetic DNA is written  in “pen” and cannot be changed, some of our genes are written in “pencil” and can be rewritten by environmental factors.

Worldwide, there’s an urban-rural divide in myopia rates. In Nepal, for example, urban children age 15 have a 27% prevalence rate while it is less than 3% for rural children the same age (Pan et al. 2012).

So what’s different for many urban kids? 

A comparative study of children ages six to seven with Chinese ancestry in Sydney and Singapore found kids in Sydney had a 3% prevalence of myopia while the same age group and ethnicity in Singapore had a 29% prevalence rate—almost ten times higher.

The study identified the most significant factor associated with the differences: time spent outdoors. The kids in Sydney spent 13.75 hours a week outdoors on average compared to just 3.05 hours for the Singapore kids (Rose et al. 2008).

The Sydney-Singapore study was one of more than a dozen studies that have zeroed in on the fact that outside sunlight helps prevent myopia.

A recent meta-analysis of myopia and outdoor time studies found that for every additional hour per week a kid spends outdoors, the chance of developing myopia drops by approximately 2% (Sherwin et al. 2012).

The single best way to protect a child’s vision is spend time outdoors in sunlight. Even if a kid is already nearsighted, increasing the time spent outdoors significantly reduced the progression of myopia.

No one is exactly sure how it works, but a recent Lancet article on myopia suggests that exposure to the sun’s rays stimulates production of the retinal transmitter dopamine, which in turn stops the eye from elongating and distorting the focus of light entering the eye (Morgan et al. 2012).

Thus, we can add myopia as another heath issue that’s linked to what Richard Louv called in his book Last Child in the Woods “nature-deficit disorder.”

Fortunately, the cure is just outside the front door. 

Parental sanity may be the chief reason parents encourage kids to play outdoors, but now at least parents can feel virtuous that it will help their kid’s eyesight as well.

References
Ip, J. M., Huynh, S. C., Robaei, D., Rose, K. A., Morgan, I. G., Smith, W., & Mitchell, P. (2007). Ethnic differences in the impact of parental myopia: findings from a population-based study of 12-year-old Australian children. Investigative ophthalmology & visual science, 48(6), 2520-2528.

Morgan, I. G., Ohno-Matsui, K., & Saw, S. M. (2012). Myopia. The Lancet, 379(9827), 1739-1748.

Pan, C. W., Ramamurthy, D., & Saw, S. M. (2012). Worldwide prevalence and risk factors for myopia. Ophthalmic and Physiological Optics, 32(1), 3-16.

Rose, K. A., Morgan, I. G., Smith, W., Burlutsky, G., Mitchell, P., & Saw, S. M. (2008). Myopia, lifestyle, and schooling in students of Chinese ethnicity in Singapore and Sydney. Archives of ophthalmology, 126(4), 527.

Sherwin, J. C., Reacher, M. H., Keogh, R. H., Khawaja, A. P., Mackey, D. A., & Foster, P. J. (2012). The Association between Time Spent Outdoors and Myopia in Children and Adolescents: A Systematic Review and Meta-analysis. Ophthalmology, 119(10):2141-51.

Image credit: Janee under a Creative Commons Attribution-Share Alike 3.0 Unported license. 

Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.

Posted In: Science

Craig Leisher is a Senior Social Scientist who focuses on amplifying and measuring the benefits to people from conservation initiatives.



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