Myopia in Chinese students more prevalent in middle-income province

The differences in myopia between two socioeconomic statuses cannot yet be explained.

Issue: March 25, 2015

The prevalence of clinically significant myopia among middle-income students in China may be almost twice that of lower-income students, according to a study.

The study looked at multiple predictors of myopia among two socioeconomic statuses in two areas within 100 km of each other in China. A large difference in myopia prevalence rates was found.

“It begs the question: How is it that these economic differences between areas are driving myopia?” principal investigator Nathan G. Congdon, MD, MPH, an OSN Glaucoma Board Member, said. “Ultimately, there has to be something that kids are doing, some kind of intermediate behavioral factor, that is causing the difference.”

Background

The study compared students from China’s economically middle-ranking administrative region of Shaanxi with students from the second poorest province of Gansu; 19,626 students were randomly selected from one class among the fourth and fifth grades from one school of each township in each of the provinces.

Clinically significant myopia was classified as uncorrected visual acuity of 6/12 or worse in either eye and a spherical equivalent of –0.5 D or worse in both eyes.

Children with uncorrected visual acuity of 6/12 or worse in either eye underwent cycloplegic refraction, while a study-specific math test was administered to determine academic achievement. The study also collected data on parental spectacle wear, children’s time spent outdoors and near/middle distance work.

Nathan G. Congdon

Results

The prevalence of myopia was 22.9% in Shaanxi students vs. 12.7% in Gansu students. Even after adjusting for other risk factors, a 70% increased risk of myopia was still associated with residence in Shaanxi. Female students overall and female students in Shaanxi had a higher risk of clinically significant myopia. Older age, a history of parents wearing glasses and higher math scores were associated with a higher myopia risk in the overall population and students in both Gansu and Shaanxi.

The differences in myopia between the two provinces cannot yet be explained.

“We expected those differences, and we expected that if we looked carefully at the kinds of behaviors that we know are associated with myopia — reading, television, playing games, video games, spending less time outdoors — we thought that would explain the difference in prevalence,” Congdon said. “In fact, it really didn’t. We adjusted for parental myopia and all of these other behavioral factors that are known, and we found there is still about a 70% higher rate of myopia among kids in [Shaanxi].”

Looking forward

The study showed that there are major differences in the prevalence of myopia among the varying socioeconomic statuses in China, but a big question remains, Congdon said.

“There’s a lot of work that we need to do in answering this question of why there are differences, why poorer areas seem to have so much less myopia,” he said. “If that can lead to a way of preventing the problem, that’s fantastic.”

While researchers continue to investigate myopia prevention in China, a study, Potentiating Rural Investment in Children’s Eyecare (PRICE), is being conducted to find sustainable models to provide glasses to children.

“Half of all the children in the world with visual disability from uncorrected refractive error live in China, some 7 million kids,” Congdon said. “We have the knowledge now that we need, and I think that a very important next step is for us to work with governments, the Chinese government, to create sustainable simple strategies for providing glasses to large numbers of children.”

The research will determine a plan to deliver free glasses to all children, available for pickup at the rural eye centers, where families will have the option to upgrade the spectacles at a cost to sustain the program, according to Congdon.

“Uncorrected refractive error is a problem we absolutely can solve, and we need to do more about it,” he said. – by Kristie L. Kahl

Reference:

Zhou Z, et al. Ophthalmology. 2015;doi:10.1016/j.ophtha.2014.12.019.

For more information:

Nathan G. Congdon, MD, MPH, can be reached at State Key Laboratory and Translational Research for Equitable Eyecare, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China; email: ncongdon1@gmail.com.
Disclosure: Congdon reports no relevant financial disclosures.