In one of the largest population-based studies ever conducted on nearsightedness in children, researchers have discovered that lower-income students in China have better vision than their middle-class counterparts. Data show that nearsightedness, also called myopia, is twice as prevalent in the middle-income province of Shaanxi compared to the poorer neighboring province of Gansu. The study was published online today in Ophthalmology, the journal of the American Academy of Ophthalmology.
In certain developed parts of East Asia, nearsightedness is skyrocketing, with the prevalence of myopia now at an estimated 80 to 90 percent of the population. In areas of the world where families cannot afford eyeglasses, poor vision from nearsightedness is a serious disability that can affect a person's ability to learn and work. Globally, 13 million children worldwide – about half of them in China – are visually impaired because of poor sight not corrected by glasses or other means, according to the World Health Organization. With those factors in mind, research teams have been scrambling to find an answer to the Asian "school myopia" crisis.
To manage this public health issue, multiple Chinese government agencies and universities, together with experts from Stanford University, have undertaken several large studies on childhood myopia. In 2012, they examined vision in nearly 20,000 fourth- and fifth-grade students: 9,489 students in Shaanxi, a middle-income province, and 10,137 students in Gansu, the second poorest province in China. The findings include the following:
- The prevalence of clinically significant myopia in the middle-income province of Shaanxi is almost 23 percent, nearly twice that of the lower-income province of Gansu, which has a 12.7 percent prevalence rate of myopia.
- Living in the middle-class area was associated with a 69 percent increased risk for nearsightedness, even after adjusting for other risk factors, such as time spent reading, outdoor activity and whether the student's parents wore glasses.
- Higher math scores were associated with increased myopia in all children.
- Nearsightedness was less prevalent in males overall.
The research team also looked at whether the use of blackboards, as opposed to textbooks, played a role in staving off myopia. Students in the lower-income area rely more on blackboards to learn in the classroom as they may have difficulty affording books, while students in the middle-income areas used blackboards less often. Researchers found that using blackboards had a "protective effect" against nearsightedness when examined as a variable alone, possibly because blackboards do not require the kind of close-up focusing that may increase myopia. However, when adjusting for other factors, they found no statistically significant differences between lower-income and middle-class students that might explain higher myopia prevalence in richer areas.
"We're still on the hunt for a plausible explanation and think the results merit more study into whether using blackboards versus books may be partially responsible for protecting eyes against nearsightedness, and what other factors may play a role," said the project's lead investigator Professor Nathan Congdon, M.D., MPH, of the Zhongshan Ophthalmic Center at Sun Yat-sen University in Guangzhou, China. "What's important is that we figure out how lower-income Chinese students have avoided nearsightedness so we can use those same strategies to prevent more childhood myopia cases across Asia and perhaps even the world."
Previous studies have found that people who had higher levels of education and years spent in school were more likely to be nearsighted. Many researchers also postulate that exposure to certain kinds of light, particularly indoor versus outdoor light, may be responsible for the uptick in myopia. Recent studies of children and young adults in Denmark and across Asia show that more time outdoors and exposure to daylight is associated with less nearsightedness.
American Academy of Ophthalmology