More and more people are nearsighted, whether they are white-collar workers, college students, high school students…even elementary school students.
But in fact, since 60 years ago, myopia has gradually “infected” many people.
In the 1980s, the prevalence of myopia in Chinese was 10% to 20%; today, the overall myopia rate among Chinese adolescents is 53.6% [1].
In 1971, the myopia rate in the United States was 25 percent [2]; in 2000, the figure was 41.6 percent; the prevalence of high myopia was approximately 4 percent [3].
In developed countries in East and Southeast Asia, the prevalence of myopia in school-age children under 12 has reached 80% to 90%[4,5]; about 20% of high school graduates suffer from high myopia [4].
Research predicts that by 2050, myopia will conquer 50% of the world’s population.
At that time, 1 in 2 people was nearsighted [5].
(Image source: soogif)
Myopia not only affects vision and appearance, but also increases the risk of a variety of diseases, such as retinal tears, retinal detachment, and cataracts, for which wearing glasses does not reduce the risk [6 ]. Myopia is also one of the leading causes of blindness worldwide [7].
Why is the myopia offensive so fierce over the years?
To put it bluntly, myopia is the inability to see distant objects. Most myopia is axial myopia, which is simply myopia caused by the lengthening of the eye axis [8].
(Note: myopia, which means that in a relaxed state, parallel rays of light enter the eye and focus in front of the retina)
Myopia is a combination of genetics and environment. The role of the two can be understood as: “Genetics loaded the bullet, environment pulled the trigger.”
Both parents are short-sighted, and their children are at higher risk for myopia. Studies have shown that children born to highly myopic parents have longer axial lengths, so they are more likely to become myopic [7].
However, the sharp increase in the number of people with myopia in the past 60 years is difficult to explain by genes alone (genes cannot have changed so much in decades), and environmental factors “have contributed”, Among them, the habit of using eyes changed the most.
Several studies have found that the more time spent outdoors, the lower the incidence of myopia.
Compared with children with frequent outdoor activities, children with short outdoor activities are 2 to 3 times more likely to be short-sighted [9].
Adding 1 hour of outdoor activity per week was associated with a 2% lower risk of myopia [10].
A 25% to 50% reduction in myopia can be observed over a period of 1-3 years with an additional 1-2 hours of outdoor activity per day, especially for children under 12 [ 6].
The trade-off between outdoor activities is indoor/screen time, and studies have found that the longer children spend indoors/screens, the higher the incidence of myopia.
In June 2020, a Ministry of Education survey of 14,532 students (primary, middle and high school) in 9 provinces found that six months myopia rate increased by 11.7%[ 10], the more time spent looking at the screen, the higher the detection rate of myopia.
A 2015 WHO report recommends 3 ways to prevent myopia:
Increase outdoor time (reduce close work)
Low-dose atropine eye drops
Wear peripheral retinal myopia defocus correction lenses (ie OK lenses, myopia defocus frames, and soft contact lenses)
Increasing time spent outdoors is the only non-medical activity that can prevent myopia, and it is also the easiest way to prevent myopia.
Outdoor activities can prevent myopia, not because of the “activity” itself. Because some studies have found that indoor exercise does not reduce the incidence of myopia [11], the focus is on “outdoors”.
A study published in 2008 found that spending more time outdoors, with or without physical activity, was associated with a lower incidence of myopia in children [12].
So what’s the magic chemistry between “outdoors” and “eye axis”?
The exact cause is unknown, but scientists have proposed many possible hypotheses.
1. Outdoor light intensity is higher, which can activate dopamine release
Outdoor illumination (brightness) is generally 10-1000 times that of indoor illumination. Bright light activates the release of human dopamine and inhibits the growth of the eye axis [12].
(Image source: soogif)
2. Larger outdoor field of vision and more relaxed eyes
When outdoors, the surrounding objects are further away, and when looking at the distance, the ciliary muscle relaxes;
Indoors, when the surrounding objects are closer, when looking at close objects, the ciliary muscle tightens and the lens becomes more convex, which induces changes in the shape of the eyeball and accelerates the progression of myopia [11] ].
3. Outdoor sun exposure promotes calcium absorption and delays myopia
Sun exposure boosts the body’s production of vitamin D, which in turn promotes calcium absorption.
Calcium deficiency reduces the elasticity and surface tension of the eye wall, increasing the risk of myopia. Studies have shown that myopic subjects have less calcium and zinc in their serum [8].
1. Expose to outdoor natural light as much as possible, preferably more than 60 minutes a day for teenagers
For adolescents, exposure to outdoor natural light for more than 60 minutes per day; children with myopia increase the time of outdoor activities to delay the development of myopia [14].
However, remember to wear sunglasses and avoid direct sunlight. Because UV exposure increases the risk of cataracts, retinal degeneration and other diseases [15].
2. Even indoors, ensure enough light to reduce the burden on the ciliary muscle
Long time indoors in low light environment and staring at the screen at close range for a long time will cause eye fatigue.
(Image source: soogif)
Even if you are working indoors, you must ensure enough light, such as turning on desk lamps and headlights, increasing the light intensity, and decompressing your eyes[16]; Play with the lights on as much as possible.
(Image source: soogif)
3. Avoid looking at near objects for a long time and reduce intraocular pressure
Looking at nearby objects for extended periods of time can increase the pressure in your eyes. High intraocular pressure increases the risk of myopia [17].
Use the 20-20-20 rule: look at the computer for 20 minutes – 20 steps away – look at the computer for at least 20 seconds [18].
Blink often to keep your eyes moist and use artificial tears if necessary.
Do some ball sports, such as table tennis, badminton, and keep your eyes moving with the ball, which can relax the eye pressure and help control myopia.
(Image source: soogif)
Said so much—
Still stand up, (while the boss is away), go out for a walk for bright eyes?
(Image source: soogif)
Reviewer: Xianmei Zhang
Deputy Director, Department of Ophthalmology, Affiliated Hospital of Hangzhou Normal University
References
[1] National Health Commission survey: more than half of children and adolescents in the country are myopic. Central People’s Government of the People’s Republic of China
[2]Vitale, S et al. 2009. Increased prevalence of myopia in the United States between 1971-1972 and 1999-2004. Arch Ophthalmol 127(12): 1632-1639.< /p>
[3]Willis, JR, et al. 2016. The prevalence of myopic choroidal neovascularization in the United States. Ophthalmology 123(8): 1771-1782.
[4]Morgan, IG, et al. 2012. Myopia. The Lancet 379: 1739-1748.
[5]Brien A. Holden, DSc, et al. Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology, Volume 124, Issue 3, March 2017, Pages e24-e25
[6]Catherine Jan et al. Prevention of myopia, China. Bulletin of the World Health Organization 2020;98:435-437. doi: http:https://dx.doi. org/10.2471/BLT.19.240903
[7]Fredrick DR. Myopia. BMJ. 2002;324(7347):1195-1199.
[8] Ophthalmology. Human Health 8th Edition
[9]Huang et al., 2015. The association between near work activities and myopia in children—a systematic review and meta-analysis. PLoS One 10(10): e0140419.
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[10]Introducing the situation of school epidemic prevention and control and education and teaching in the fall semester of 2020, Ministry of Education of the People’s Republic of China
[11] Smith EL, Hung L-F, Huang J. Relative peripheral hyperopic defocus alters central
refractive development in infant monkeys. Vision Res 2009;49:2386C92.
[12]BARLOW HB. Temporal and spatial summation in human vision at different background intensities. J Physiol. 1958;141(2):337-350.
[13]Lingham G, Mackey DA, Lucas R, Yazar S. How does spending time outdoors protect against myopia? A review. Br J Ophthalmol. 2020 May;104(5):593 -599.
[14]http:https://www.moe.gov.cn/srcsite/A17/moe_943/s3285/201808/t20180830_346672.html
[15]van Kuijk FJ. Effects of ultraviolet light on the eye: role of protective glasses. Environ Health Perspect. 1991;96:177-184.
[16]J R Gaddy, M D Rollag, G C Brainard, Pupil size regulation of threshold of light-induced melatonin suppression, The Journal of Clinical Endocrinology & Metabolism, Volume 77, Issue 5, 1 November 1993, Pages 1398C1401.
[17]T Wong, P Mitchell, The eye in hypertension. The Lancet, 2007
[18]https:https://www.aoa.org/healthy-eyes/eye-health-for-life/adult-vision-19-to-40-years-of -age?sso=y
Author: Zhang Xiaoyi
Editors: Zhang Xiaoyi, Ye Zhengxing
Proofreading: Wu Yihe | Typesetting: Li Yongmin
Operation: Han Ningning | Coordinator: Wu Wei