Lower-income students in China have less myopia

Researchers in China have discovered that lower-income students have much lower levels of myopia than their middle-class counterparts. Data from a study of 20,000 children show that myopia is twice as prevalent in the middle-income province of Shaanxi compared to the poorer neighbouring province of Gansu. The study was published online in Ophthalmology.

In a study that began in 2012, researchers from multiple Chinese government agencies and Stanford University 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. They found:

• The prevalence of clinically significant myopia in the middle-income province of Shaanxi is almost 23%, nearly twice that of the lower-income province of Gansu (12.7%).

• Living in the middle-class area was associated with a 69% 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. 

• Myopia 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; students in the middle-income areas used blackboards less often. The 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, the researchers 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, MD, 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.”