In recent years, more and more studies have shown that outdoor activities can delay the progression of myopia. For example, a study in Guangzhou showed that compared with normal life, children who added 40 minutes of outdoor classes every day had a 10% lower cumulative incidence of myopia within 3 years [1]. A study in Taiwan also found that children who spend 40 minutes in outdoor classes every week are Children who were active outdoors for 11 hours with light intensity greater than 1,000 lux had a significant myopia protection effect compared to children in the control group. [2]
This finding is also well understood from an evolutionary perspective.
Like other species, humans are also products of the environment. In their long history, humans have lived more of a life of hunting, gathering, and farming. These are all outdoor activities, and our eyes are also “made” to adapt to outdoor life. .
After entering industrial civilization, we spend more and more time indoors and do less and less outdoor activities. Our eyes have changed from looking outdoors to looking at close objects such as indoors, books, and computers. Naturally, we have become uncomfortable.
The incidence of myopia has also begun to increase exponentially in recent decades, so to a certain extent, myopia is a modern disease that appears along with changes in lifestyle.
Why can the outdoors have the effect of preventing myopia? The mechanism is not very clear at present, but it is speculated that there may be two reasons, one is increased sunlight exposure, and the other is reduced use of eyes at close range. Among them, sunlight exposure may be a more important factor, and the mechanism may be that sunlight stimulates retinal dopamine secretion and thereby changes the long axis of the eye [3].
Therefore, from the perspective of preventing myopia, we should let our children spend more time outdoors like the ancients, and we should not give them sunhats, sunglasses and the like.
But myopia is clearly not the only eye health issue we should be concerned about. There is now clear evidence that UV exposure increases the risk of cataracts, pterygium, ocular skin cancer and other problems.
From an evolutionary perspective, cataracts may still affect survival, but before the advent of modern medicine, the average life span of humans was less than 40 years old, and the probability of encountering these problems was relatively small, making these problems less prominent. Now that the average life expectancy of people in our country is more than 70 years old, cataracts have become more prominent, and they are an important cause of visual impairment and even blindness. [4]
So when choosing your sun exposure, you have to weigh the risk of problems like myopia and cataracts.
Will wearing sunglasses affect the prevention effect of myopia? Unfortunately, there is currently no very systematic research and there is no very clear answer to this question.
In recent years, some people have indeed paid attention to this issue. A study in Singapore [5] evaluated the impact of wearing sunglasses and hats on light intensity outdoors. The test found that the light intensity of wearing sunglasses (1792-6800 lux) was lower than that of wearing sunglasses in the shade (555-7786 lux) and Wearing a hat (416-8156 lux), but still much higher than indoors (112-156 lux), also meets the 1000 lux threshold required to prevent myopia, so the author believes that wearing sunglasses or hats outdoors does not affect the effect of preventing myopia. .
But the above research is not direct evidence. The mechanism of outdoor activities to prevent myopia in children is not very clear. Is it simply related to the intensity of light? Or is it related to the specific light in natural light? Or is it related to exposure time? There is no clear conclusion yet.
Studies have found that red light, green light, blue light, and ultraviolet light can all inhibit myopia [6], but ultraviolet light is the most effective light in inhibiting myopia [7]. Therefore, this Japanese research team is also trying to develop a light that can transmit 360-400nm ultraviolet light but Sunglasses that filter out other harmful rays.
But as mentioned before, the current research is not in-depth enough on whether wearing sunglasses outdoors will affect the effect of preventing myopia, and there is no very clear conclusion because the mechanism is not very clear and there are many variables behind it, such as exposure. The intensity and duration of sunlight, as well as the myopia protection effect itself for children of different ages, may be different, and the impact of wearing sunglasses on the effect may also be different.
In contrast, it is clear that long-term UV exposure increases the risk of problems such as cataracts and pterygium. At present, the American Academy of Ophthalmology and the Academy of Pediatrics also clearly recommend that children should wear sunglasses when doing anything in the sun. [8]
Of course, the incidence of myopia is higher in China. Each parent may have his or her own value choice on how to weigh myopia prevention against cataracts and other ultraviolet damage. The above information can be used as a reference when making your own choices.
However, ultraviolet rays are more harmful when the sun is strong. Even if you want to spend more time outdoors to prevent myopia, you should avoid these moments. If you cannot avoid it, you should wear sunglasses and protect your skin from the sun.
References:
[1]https://pubmed.ncbi.nlm.nih.gov/26372583/
[2]https://pubmed.ncbi.nlm.nih.gov/29371008/
[3]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5653403/
[4]https://www.who.int/zh/news-room/fact-sheets/detail/blindness-and-visual-impairment
[5]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6656201/
[6]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8624215/
[7]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8179197/
[8]https://publications.aap.org/pediatrics/article/127/3/588/64968/Ultraviolet-Radiation-A-Hazard-to-Children-and?autologincheck=redirected
