The effects of outdoors on Myopia

The following article is presented to you by Pablo Sanz and Miguel García
Disclaimer: For all the general public and specialists, some technical knowledge might be required.

Let en-light our blog, pick our sunglasses and let´s talk about the influence of outdoor time on the onset, development as well as progression of myopia. Besides, as far as 100 years ago (1), some studies started to conjecture about ambient light and its impact on the development of the eye. Starting to be considered as plausible public action to stop myopia prevalence increase, especially in those areas with high risk of development such as East Asia, the topic triggered interest again.

For more in-depth treatment of the issue of outdoors effect we should keep in mind different terms such as time exposure and light intensity, because many factors could contribute to this “shielding effect“.

During the last years a large number of research studies investigated the hypothesis that time spent outdoors protects against the development and progression of myopia.

Since the beginning of this hypothesis, all researches pointed to this direction. Earlier, it was shown in chickens (2) and children that ambient light plays an important role at compensation of myopic defocus and onset of myopia. While at early stages in humans, it was though that physical activity could have a major input, Rose et al (3) showed that light conditions where the key.

To get a better overview on this matter we should introduce the sentence scientific evidence.

  • But what´s evidence?

In a scientific environment, there is no place for believes, and the evidence relies in the studies published and their repeatability. If we want to grade the evidence they give, we do so according to the type of article, as following pyramid illustrates.

Evidence piramyd
Fig 1. Pyramid of evidence

As pointed out by the pyramid, meta-analysis are the highest source of evidence in science. And a recent meta-analysis from Xiong et al, 2017 (4), analyzed over 25 studies and they concluded that time outdoors prevent the development, but has no effect on slowing progression of eyes that are already myopic.

Other studies that looked into the possible use of longer outdoor hours to prevent myopia (5) as public policies, concluded that an extra hour could have greater impact on the onset and development of myopia in children between 5 to 8 years. Similar recommendation were given by He et al 2015,(6) where they claimed that 45 min of outdoor activities for schools in China could prevented myopia onset.

“Although research about understanding the exact mechanism is still underway, based on current results approximately 3 hours of outdoor activity during a day may be considered protective against myopia.”

– Verkicharla, 2016 (7)

  • Do we know exactly how it works?

Short answer is NO, albeit different theories have been exposed, it is still unclear (8).

So far we know that some factors that can mediate are the light intensity which differs from indoors and the spectrum from this light.(9)

In this framework, it is particularly relevant to mention luminous intensity. In outdoors the intensity of light is incredibly higher compared to the intensity indoors. In summer, the outdoor luminous intensity at noon may reach levels over 100,000 lux. Conversely, the typical indoor luminous levels in an employment office is around 300 to 500 lux.

This light conditions can influence, but how we think it does?

1) It can increase Vitamin D, which promotes the gene expression of an essential enzyme involved in the synthesis of Dopamine.(10,11)

We would talk more about the pharmacological pathways in another posts.

Dopamine pathway in Myopia (Not available yet)

Pharmacological pathways in Myopia (Not available yet)

2) The bio-marker UVAF (representing the amount of exposure to this light spectrum) was increased in the conjunctiva of children that spent more time in outdoors.(12,13)

It is known that UVA-light and blue light is more present in outdoor than in indoor conditions and it might it be that it is acting as a trigger for cross-linking of collagen structures in the eye.

Cross-linking is being tested for reinforce the collagen patterns in the eye, so this could be a potential protective role on the myopia progression. (14) However, currently there are no studies in humans and few of them in animals. Further studies are required to expand this hypothesis.

3) The different spectrum with more blue and green environments.

Chromatic aberration scheme, img from Wikip
Fig 2. Chromatic aberration

When we consider the development of myopia as visual guided and if we look how the different light wavelengths arrive to our retina, we can see that blue light focuses in front of the retina.
The absence of Violet Light Spectrum in indoors  has been recently proposed to be related to this myopia prevention. (15)

  • How we should manage?

For different reasons (cultural, ideological, technological leisure etc.), the time we stay in the outside has decreased. Some cultures give special relevance on education and competitiveness during the school period, forgetting how important is to have spare time for the children and how important is to pass it outside.

As changing the behavior is hard,  some ideas pop-up, such as the so-called “bright light classroom”, where the classroom´s walls and ceilings are made of see-through plastic that allows the sunlight get in. The main idea behind this to create a potential way to increase the amount of light and simultaneously allow children to continue their education.

It is our duty to complete the knowledge of how this works,  and to apply this findings into our daily life.

  • Conclusions

-We encourage all the children to spend more time outdoor.

-The way it works is unclear and can be a mixture of all the theories proposed.

-But we remind the importance of protect ourselfs from the sun too, by using sunglasses, in order to avoid pathologies… Sun and eyes (AAO).

Stay up-to-date, Keep on reading and

Myopia in Science!

  • References.
1. Cohn H. Handbook of the Hygiene of the Eye. Vienna and Leipzig: Urban & Schwarzenegger; 1892.
1b. Read SA. Ocular and Environmental Factors Associated with Eye Growth in Childhood. Optom Vis Sci. 2016;93(9):1. doi:10.1097/OPX.0000000000000915.
2. Ashby R, Ohlendorf A, Schaeffel F, P M, IG M, JA M. The Effect of Ambient Illuminance on the Development of Deprivation Myopia in Chicks. Investig Opthalmology Vis Sci. 2009;50(11):5348. doi:10.1167/iovs.09-3419.
3. Rose KA, Morgan IG, Ip J, et al. Outdoor Activity Reduces the Prevalence of Myopia in Children. Ophthalmology. 2008;115(8):1279-1285. doi:10.1016/j.ophtha.2007.12.019.
4. Xiong S, Sankaridurg P, Naduvilath T, et al. Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review. Acta Ophthalmol. 2017:1-16. doi:10.1111/aos.13403. 
5. Shah RL, Huang Y, Guggenheim JA, Williams C. Time Outdoors at Specific Ages During Early Childhood and the Risk of Incident Myopia. Investig Opthalmology Vis Sci. 2017;58(2):1158. doi:10.1167/iovs.16-20894. 
6. He M, Xiang F, Zeng Y, et al. Effect of time spent outdoors at school on the development of myopia among children in China a randomized clinical trial. JAMA - J Am Med Assoc. 2015;314(11):1142-1148. doi:10.1001/jama.2015.10803. 
7. Verkicharla PK, Chia NEH, Saw S-M. What Public Policies Should Be Developed to Cope with the Myopia Epidemic?. Optom Vis Sci. 9000;Publish Ah(9):1055-1057. doi:10.1097/OPX.0000000000000982.
7b. Lin Z, Vasudevan B, Jhanji V, Mao GY, Gao TY, Wang FH, Rong SS, Ciuffreda KJ, Liang YB. Near work, outdoor activity, and their association with refractive error. Optom Vis Sci 2014;91:376Y82. 
8. French AN, Ashby RS, Morgan IG, Rose KA. Time outdoors and the prevention of myopia. Exp Eye Res. 2013;114:58-68. doi:10.1016/j.exer.2013.04.018. 
9. Ngo C, Saw SM, Dharani R, Flitcroft I. Does sunlight (bright lights) explain the protective effects of outdoor activity against myopia? Ophthalmic Physiol Opt. 2013;33(3):368-372. doi:10.1111/opo.12051. 
10. Tideman JWL, Polling JR, Voortman T, et al. Low serum vitamin D is associated with axial length and risk of myopia in young children. Eur J Epidemiol. 2016;31(5):491-499. doi:10.1007/s10654-016-0128-8. 
11. Kwon J, Choi JA, La TY. Serum 25-hydroxyvitamin D level is associated with myopia in the Korea national health and nutrition examination survey. Medicine (Baltimore). 2016;95(46):e5012. doi:10.1097/MD.0000000000005012. 
12. Sherwin JC, Hewitt AW, Coroneo MT, Kearns LS, Griffiths LR, Mackey DA. The Association between Time Spent Outdoors and Myopia Using a Novel Biomarker of Outdoor Light Exposure. Investig Opthalmology Vis Sci. 2012;53(8):4363. doi:10.1167/iovs.11-8677. 
13. Haworth KM, Chandler HL. Seasonal Effect on Ocular Sun Exposure and Conjunctival UV Autofluorescence. Optom Vis Sci. 2017;94(2):219-228. doi:10.1097/OPX.0000000000001014. 
14. Liu S, Li S, Wang B, et al. Scleral Cross-Linking Using Riboflavin UVA Irradiation for the Prevention of Myopia Progression in a Guinea Pig Model: Blocked Axial Extension and Altered Scleral Microstructure. Zeugolis D, ed. PLoS One. 2016;11(11):e0165792. doi:10.1371/journal.pone.0165792.
15. Torii H, Kurihara T, Seko Y, et al. Violet Light Exposure Can Be a Preventive Strategy Against Myopia Progression. EBioMedicine. 2017;15:210-219. doi:10.1016/j.ebiom.2016.12.0070.

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