Rogers Hornsby was one of the most outstanding hitters in baseball history, but he had a bad reputation as a “cold-hearted king”. Teammates complained that he didn’t socialize and wouldn’t even go to the most popular event of the time (1920s), the movies. Hornsby often said that sitting in a dark movie theater staring at a bright screen would make him miss the ball. It was really hard to argue with him in this regard. After all, he had extraordinary eyesight, having averaged over 400 hits in three seasons.
There may be some truth in Hornbeith’s words, but only recently have scientists begun to accept that spending too much time indoors can lead to myopia.
In recent decades, the incidence of myopia has been rising in North America and Europe, and one third of adults in the United States are now nearsighted. This number is enough to cause concern in itself. In contrast, however, the climb in myopia rates in East Asia has reached alarming proportions. Recent surveys of young people in Seoul, South Korea, and college students in Shanghai, China, show myopia rates of more than 95 percent. In some other central cities in the Far East, the spike in myopia rates is not to be underestimated.
It was only a few years ago that studies found a link between myopia and too little outdoor activity as a child. At the time, many researchers were taken aback – the idea that children’s play might promote normal eye development sounded incredible.
”Indeed, five years ago, I don’t think anyone would have paid attention to how much time people spent outdoors,” says optometrist Jeremy Guggenheim. He has studied myopia in Wales, England, and currently works at the Hong Kong Polytechnic University. He believes the findings bring “exciting new directions” to myopia research.
The idea that by spending more time outdoors as a child, many people might not need frames, contact lenses or laser surgery to correct their vision – these ideas are fascinating to think about. But Guggenheim pointed out that it is not clear how much staying outdoors will reduce the risk of myopia, or what the exact mechanism is. Some scientists say the trick may be to bask in the natural light, may be in the extreme long-range relaxation of the eyes, may also be the role of the outdoor environment in the afterglow scenery, or of course, may be the result of a combination of these factors.
Donald Mutti, an optometrist at the Ohio State University College of Optometry, said, “A lot of questions are up in the air, which prevents us from giving effective enough advice.”
In addition to staying outdoors, other behaviors may also have an impact. Today’s record high myopia rates coincide with the growth of an entire generation of children who grew up with computers and video games and were pressured by the heavy pressure to advance to higher education (this is especially evident in the Far East). Some researchers refer to a long-debated theory that myopia is related to excessive reading and other “near work” (near work).
The jury is still far from out on this issue. But at least in Guangzhou, China, clinical trials related to myopia have been conducted. Some randomly selected children will participate in an extra hour of outdoor activity at school each day. As data from the trial accumulates, this strategy is already showing results.
Nearsightedness is rife
If you think of the human body as an instrument, I’m afraid the eyes are among the most delicate parts. People with excellent vision can see objects near at hand without much effort. To see objects close at hand, the eye muscles that control the lens contract to focus the image of the object on the retina at the back of the eye. It is also trivial for a person with good vision to see distant objects because the eye muscles relax and the lens changes shape to be able to focus the distant image onto the retina.
However, myopic patients have a slightly elongated eye, which poses a problem. Their eyes can still see near objects, but distant objects are imaged a little in front of the retina, and they are left with a blur in front of their eyes.
For people with excellent vision, the lens of the eye just focuses the image on the retina. They can see clearly, both near and far. However, in myopic people, the eye is elongated so that distant objects are focused only on the front of the retina, and the image becomes blurry. The shape of the eye is determined by its growth process, which occurs primarily during infancy and continues to grow, but to a limited extent, during the adolescent stage. The growth of the eye is largely controlled by genetic instructions that have been created over millions of years of evolution. If the genetic template is defective, vision will of course be affected. But eye growth is also heavily dependent on a number of external factors – a process that scientists call visual feedback. The “bombardment” of the eye by light, including the color and contrast of light and dark, can play a role in guiding the normal growth of the eye.
Scientists can now be confident that this external stimulus has undergone some changes in recent decades, leading to the prevalence of myopia in the youth population. From the early 1970s to the turn of the century, the myopia rate rose from 25 percent to nearly 42 percent among 12- to 54-year-olds in the U.S. alone, such a dramatic change in just one generation. Among young people in the United States, the figure also rose from 28 percent in the 1970s to 38 percent. On the other side of the globe, Singapore’s myopia rate is even more worrisome – as the country has grown from a silent port city to an international trade center, the myopia rate among Singapore’s active-duty military (all young men) has soared from 43 percent in the late 1980s to more than 80 percent today.
Meanwhile, the older generation has not seen a significant increase in myopia rates. In China and the United States, the myopia rate among people over 40 years old is about 1 in 4.
Because the surge in myopia has not hit the countryside, scientists believe the myopia frenzy reflects a new type of behavior among younger urban dwellers. As more people flock to cities, the situation is likely to get worse. For some people, myopia will be nothing more than a minor inconvenience to life. But for others with high levels of myopia, their vision will deteriorate and they will be at greater risk for cataracts, glaucoma and retinal detachment in later life. Among young people in Seoul and students in Shanghai, almost one in five people with myopia is highly myopic.
Seang-Mei Saw, an internist and epidemiologist at the National University of Singapore, said, “Etiologic myopia and co-morbid blindness will be prevalent in Asia in the coming decades.” In 2007, Muti and his team at Ohio State University recruited 514 sighted third-grade children and analyzed their similarities and differences over the next five years. 5 years later, 1 in 5 children were myopic. Even when parental myopia was factored in, the team found that children who spent more time outdoors were less likely to develop myopia than those who were often shut out of the house. The study was published in the journal Ophthalmology & Vision Science (Investigative Ophthalmology & Visual Science).
In 2008, Ian Morgan of the Australian National University and Kathryn Rose of the University of Sydney also found a correlation between myopia and outdoor activity. Children who spend a lot of time outdoors before the age of 10 are less likely to develop myopia, whether it’s relaxing or playing sports. Writing in Ophthalmology, they noted that indoor exercise did not appear to have the same effect. In addition, the two researchers found no clear evidence that working at close range is harmful to the eyes. Just staying outdoors has an effect. Follow-up studies done in China, Singapore and the United States support these results.
These reports are a far cry from what people thought decades ago, when many scientists still believed that myopia was primarily a genetic problem. After all, if one parent is myopic, the risk of myopia in the child increases, and the risk is even higher if both parents are myopic. However, scientists have yet to find hard evidence at the genetic level that could be called the cause of myopia. According to Nature Genetics in 2010 and Human Genetics in 2012, two international teams of researchers have found many genetic variants that appear more frequently in people with myopia. However, Guggenheim said, “These are only subtle genetic effects that can only explain a small percentage of myopia cases.” In addition, one study comparing Chinese children who lived in different environments and spent different amounts of time outdoors showed that ethnicity-related genetic similarities were far less important than daily behavioral patterns.
Morgan said the myopia frenzy has nothing to do with genetics. “The gene pool can’t change that much in one generation, even if it doesn’t reach several generations,” he said, “and we’ve found a compelling new causative factor, and that’s time spent outdoors.” Studies have shown that the incidence of myopia varies across ethnic groups depending on whether people live in rural or urban areas (data from different countries may not be comparable); urban living appears to have adverse effects on the eyes.