More and more people around are short-sighted, whether it is white-collar workers, college students, high school students... Even elementary school students.
But in fact, since 60 years ago, myopia has gradually begun to "infect" many people.
In the 1980s, the prevalence of myopia in Chinese was 10% to 20%, while today, the overall myopia rate of adolescents in mainland China is 53.6%[1].
In 1971, the myopia rate in the United States was 25%[2]; in 2000, the number was 41.6%; the prevalence of high myopia was about 4%[3].
In developed countries of East and Southeast Asia, the prevalence of myopia among school-age children under 12 years of age has reached 80 to 90 percent [4,5]; about 20 percent of high school graduates have high myopia [4].
Research predicts that by 2050, myopia will conquer 50% of Earthlings.
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 rifts, retinal detachment, cataracts, etc., and wearing glasses does not reduce the risk of these diseases [6]. Myopia is also one of the leading causes of blindness worldwide [7].
Why has the myopia offensive been so ferocious over the years?
To put it bluntly, myopia is the inability to see things in the distance. Most myopia is axial myopia, which is simply myopia caused by the lengthening of the eye axis [8].
(Note: Myopia refers to the fact that when in a relaxed state, parallel light rays enter the eye and focus on the front of the retina)
Myopia is the result of a combination of genetics and the environment. The role of both can be understood as: "Genetics is loaded with bullets, and the environment pulls the trigger." ”
Parents are myopic, and children are at higher risk of myopia. Studies have shown that highly myopic parents give birth to children with longer eye shafts and are therefore more likely to become myopic [7].
However, the sharp rise in the number of myopia in the past 60 years is difficult to explain by genes alone (genes cannot change so much in decades), and environmental factors are "indispensable", of which eye habits have changed the most.
Multiple studies have found that the longer you spend outdoors, the lower the incidence of myopia.
Children with short outdoor activities are 2 to 3 times more likely to have myopia than children who spend frequent outdoor activities [9].
By increasing the amount of time spent outdoors by one hour per week, the odds of myopia are reduced by 2% [10].
A 25 to 50 percent reduction in myopia rates can be observed with additional outdoor activities for 1 to 2 hours a day over a period of 1 to 3 years, especially for children under 12 years [6].
The time in front of the screen is indoors/screen time, and the study found that the longer the child spends indoors/screens, the higher the incidence of myopia.
In June 2020, the Ministry of Education surveyed 14,532 students (primary, middle and high school) in nine provinces and found that the half-year myopia rate increased by 11.7% [10], and the more time spent looking at the screen, the higher the detection rate of myopia.
In a 2015 WHO report, 3 ways to prevent myopia were recommended:
Increased outdoor activity time (reduced close working)
Low-dose atropine eye drops
Wear peripheral retinal myopia defocus correction mirrors (i.e. OK mirrors, myopia defocus frame mirrors, and flexible contact lenses)
Increasing the time spent outdoors is the only non-medical activity that can prevent myopia, and it is also the simplest way to prevent myopia.
Outdoor activities prevent myopia from occurring, not because of the "activity" itself. Because 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, regardless of physical activity, reduced the incidence of myopia in children [12].
So what's the magical chemistry that happens between "outdoors" and "eye axis"?
The exact reason is not yet known, but scientists have proposed many possible hypotheses.
1. The outdoor light intensity is higher and can activate the release of dopamine
Outdoor illuminance (brightness) is generally 10 to 1000 times that of indoor lighting, and bright light activates the release of dopamine from the human body and inhibits the growth of the eye axis [12].
2. The outdoor field of view is larger and the eyes are more relaxed
When outdoors, things around are farther away, and when looking into the distance, the ciliary muscles relax;
Indoors, the surrounding things are relatively close, and when looking close, the ciliary muscles are tightened and the lens is 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
Sunshine promotes the body's production of vitamin D, which promotes the absorption of calcium.
Calcium deficiency weakens the elasticity and surface tension of the eye wall and increases the risk of myopia. Studies have shown that myopic people have less calcium and zinc in their serum [8].
1, as far as possible to contact outdoor natural light, teenagers are best more than 60 minutes a day
Adolescents are exposed to natural outdoor light for more than 60 minutes a day; children with myopia increase their outdoor activity time and delay myopia development [14].
However, remember to wear sunglasses to avoid direct sunlight. Because ultraviolet radiation increases the risk of diseases such as cataracts and retinal degeneration [15].
2, even indoors, to ensure sufficient light, reduce the burden of ciliary muscles
Long time in the indoor low-light environment, long time close to the screen, will make the eyeball fatigue.
Even if you work indoors, you must ensure enough light, such as turning on table lamps and headlights, increasing the light intensity, and reducing the pressure on the eyes [16]; when you stay up late to play with your mobile phone, you must also try to turn on the lights to play.
3. Avoid looking at close objects for a long time and reduce intraocular pressure
Looking at objects up close for a long time will raise your eye pressure. High intraocular pressure increases the risk of myopia [17].
Use the 20-20-20 principle: look at the computer for 20 minutes— 20 steps away — for at least 20 seconds.
Blink your eyes often to keep your eyes moist, and use artificial tears if necessary.
Perform some ball sports, such as table tennis, badminton, so that your eyes follow the ball constantly, you can relax the intraocular pressure, help control myopia.
Having said all that —
Still don't get up, (while the boss is away), for the sake of bright eyes, go out for a walk?
Reviewer: Zhang Xianmei
Deputy Director of the Department of Ophthalmology, Affiliated Hospital of Hangzhou Normal University
bibliography
[1] Survey by the National Health Commission: More than half of the children and adolescents in the country are myopic. The 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.
[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://dx.doi.org/10.2471/BLT.19.240903
[7] Fredrick DR. Myopia. BMJ. 2002;324(7347):1195-1199.
Ophthalmology. Human Guard 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.
[10] Introduction to the epidemic prevention and control and education and teaching work in schools 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;49:2386–92.
[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://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 1398–1401.
[17] T Wong, P Mitchell, The eye in hypertension. The Lancet, 2007
[18]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