Can early morning walks help stave off nearsightedness?

Myopia, or nearsightedness, among humans has been steadily increasing throughout the past century. Before 2000, the prevalence of myopia never exceeded 50% of the population in any region of the world. However, if current trends continue, by 2050, the prevalence will exceed 50% in 57% of the world’s nations.1 Already, ophthalmology surveys conducted in 2008–2012 reveal that 64.6% of South Koreans aged 5–18 years are developing myopia.2 By the time South Koreans reach 20 years of age, 96% have myopia. South Korea is not alone, as the figure shows.

Figure: Myopia Rate among 20-Year-Olds in Asia
Credit: Ian G. Morgan et al., “The Epidemics of Myopia: Aetiology and Prevention,” Progress in Retinal and Eye Research 62 (January 2018): 134–149, doi:10.1016/j.preteyeres.2017.09.004, Creative Commons Attribution

Myopia Source
Increasing myopia appears to correlate with society’s increasing education, urbanization, and indoor lifestyle. Hence, many ophthalmologists have speculated that something about being outdoors plays a significant role in preventing the onset of at least certain kinds of myopia. Indeed, several studies affirm that outdoor activity has a protective effect on the development of myopia.3 Other studies show that visible violet light (360–400 nanometers) protects against myopia development in mice, chicks, and humans.4 Outdoor sunlight has an abundance of light at these wavelengths while glass windows and doors block all wavelengths below 400 nanometers and artificial light sources emit virtually no light at less than 400 nanometers.5

Myopia Cause
A team of nine research ophthalmologists in Japan and the United States led by Xiaoyan Jiang sought to discover the underlying effect that explains why visible violet light protects against myopia development.6 They found that for mice, the protective effect depends on neuropsin, otherwise known as OPN5. Neuropsin supports the development of the vascular choroid layer, which nourishes the retina in the eyeball.

It takes a robust choroid to ensure that the eyeball shape remains normal. Myopia occurs when the eyeball becomes elongated along the visual axis.

The eyeball’s need for neuropsin explains the benefit of exposure to visible violet light. This light activates neuropsin. The neuropsin, in turn, activates the local circadian clock in the retina. For this clock to operate so as to prevent elongation of the eyeball (the inducement of myopia) it is necessary to be exposed to visible violet light at the right time of the day. The right time for mice, which are nocturnal animals, is just before sunset. For humans, the right time is just after dawn.

Design Implications
Our eyesight and the eyesight of most mammals is amazingly acute for both up close and distant viewing. It is also amazingly enduring. It must be for mammals to function at high activity levels and to perform a wide range of functions. Nowhere is this more true than for humans.

Unlike other mammals, humans have been able to tolerate a loss of eyesight acuity and function thanks to technology. One reason why the recent rapid increase in myopia among humans has not been considered a catastrophe is that it is so easy to treat and correct. A simple pair of glasses is sufficient to restore eyesight loss.

Before modern technology, however, certain design features in the natural realm kept myopia development in check. As I have explained in previous articles,7 our Sun is a star like no other. It showers the just-right radiation intensity and spectrum upon Earth to optimize our eyesight. Our planet’s atmosphere, especially its stratospheric ozone layer, is fine-tuned to block out deadly solar ultraviolet radiation (radiation shorter than 300 nanometers). But it allows the just–right amount of longer wavelength ultraviolet radiation (300–360 nanometers) to reach Earth’s surface to sustain vitamin D production in our skin and the operation of several other life-critical biochemical synthesis reactions. It is also fine-tuned to allow the just–right amount of visible violet radiation (360–400 nanometers) to reach Earth’s surface to stave off myopia development. Our eyes, and the eyes of most mammals, are designed so that regular exposure to visible violet light at the just–right times of each day maintains the necessary eyeball shape for optimal vision.

How Should We Then Live?
In light of what we now know about our eyes and how our solar and terrestrial environments have been fine-tuned to make possible several decades of optimal vision, we should first offer up thanks for what our Creator has so generously provided on our behalf. One way we can show our appreciation is to spend time outdoors and take advantage of his way to mitigate myopia development rather than rely on our technological fixes. After all, it is easy to misplace, lose, or damage our glasses or contact lenses, and find ourselves in a serious predicament.

Furthermore, there are other benefits to spending regular time outdoors shortly after dawn. Such regular exposures set and stabilize circadian rhythms beyond those in our eyes. Combining such exposures with strenuous exercise enhances both our physical and mental health. Instead of gulping down a cup of coffee and checking email after sleeping in and then heading for the office, our body, brain, and eyes, according to the nine ophthalmologists, will benefit from getting up earlier and going for a walk or a run in the great outdoors.

Check out more from Reasons to Believe @Reasons.org

Endnotes

1. Brien A. Holden et al., “Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050,” Ophthalmology 123, no. 5 (May 2016): 1036–42, doi:10.1016/j.ophtha.2016.01.006.
2. Dong Hui Lim et al., “The High Prevalence of Myopia in Korean Children with Influence of Parental Refractive Errors: The 2008–2012 Korean National Health and Nutrition Examination Survey,” PLOS ONE 13, no. 11 (November 26, 2018): id. 0207690, doi:10.1371/journal.pone.0207690.
3. Kathryn A. Rose et al., “Outdoor Activity Reduces the Prevalence of Myopia in Children,” Ophthalmology 115, no. 8 (August 1, 2008): 1279–85, doi:10.1016/j.optha.2007.12.019; Xiaoyan Jiang et al., “Progress and Control of Myopia by Light Environments,” Eye & Contact Lens 44, no. 5 (September 2018): 273–78, doi:10.1097/ICL.0000000000000548; Xiangui He et al., “Shanghai Time Outside to Reduce Myopia Trial: Design and Baseline Data,” Clinical & Experimental Ophthalmology 47, no. 2 (March 2019): 171–78, doi:10.1111/ceo.13391.
4. Hidemasa Torii et al., “Violet Light Exposure Can Be a Preventive Strategy against Myopia Progression,” EBioMedicine 15 (February 1, 2017): 210–19, doi:10.1016/j.ebiom.2016.12.007; Hidemasa Torii et al., “Violet Light Transmission Is Related to Myopia Progression in Adult High Myopia,” Scientific Reports 7, no. 1 (November 6, 2017): id. 14523, doi:10.1038/s41598-017-09388-7; Ryan Strickland, Erica G. Landis, and Machelle T. Pardue, “Short-Wavelength (Violet) Light Protects Mice from Myopia through Cone Signaling,” Investigative Ophthalmology & Visual Science 61, no. 2 (February 2020): id. 13, doi:10.1167/iovs.61.2.13.
5. Torii et al., “Violet Light Exposure.”
6. Xiaoyan Jiang et al., “Violet Light Suppresses Lens-Induced Myopia Via Neuropsin (OPN5) in Mice,” Proceedings of the National Academy of Sciences, USA 118, no. 22 (June 1, 2021): e2018840118, doi:10.1073/pnas.2018840118.
7. Hugh Ross, “Our Sun Is Still the One and Only,” Today’s New Reason to Believe (blog), April 17, 2017 https://reasons.org/explore/blogs/todays-new-reason-to-believe/our-sun-is-still-the-one-and-only; Hugh Ross, “Search for the Sun’s Twin,” Today’s New Reason to Believe (blog), March 17, 2008, https://reasons.org/explore/blogs/todays-new-reason-to-believe/search-for-the-suns-twin; Hugh Ross, “How Did the Sun End Up with Its Unique Rocky Planets?”, Today’s New Reason to Believe (blog), May 17, 2021, https://reasons.org/explore/blogs/todays-new-reason-to-believe/how-did-the-sun-end-up-with-its-unique-rocky-planets-2; Hugh Ross, “It Takes a Dull Star to Have a Great Party,” Today’s New Reason to Believe (blog), July 6, 2020, https://reasons.org/explore/blogs/todays-new-reason-to-believe/it-takes-a-dull-star-to-have-a-great-party.