Sunlight needed to prevent myopia
Look and you shall see: A generation of real-life nearsighted Mr. Magoos is growing up before your eyes. A largely unrecognized epidemic of nearsightedness, or myopia, is afflicting the eyes of children.
People with myopia can see close-up objects clearly. But their distance vision is blurry, and correction with glasses or contact lenses is likely to be needed for activities such as seeing the blackboard, cycling, driving or recognizing faces down the block.
The growing incidence of myopia is related to changes in children’s behavior, especially how little time they spend outdoors. Gone are the days when most children played outside between the end of the school day and suppertime.
Susceptibility to myopia is determined by genetics and environment. Children with one or both nearsighted parents are more likely to become myopic. However, while genes take many centuries to change, the prevalence of myopia in the United States increased from 25% in the early 1970s to nearly 42% just three decades later. And the rise in myopia is not limited to highly developed countries. The World Health Organization estimates that half the world’s population could be myopic by 2050.
Given that genes don’t change that quickly, environmental factors, especially children’s decreased exposure to outdoor light, are the likely cause of this rise in myopia, experts say. Consider, for example, factors that keep modern children indoors: an emphasis on academic studies and homework, the irresistible attraction of electronic devices and safety concerns that demand adult supervision during outdoor play.
HASTENING MYOPIA
Recent research suggests that months of covid-induced confinement could be hastening myopia’s silent progression among young children. A Canadian study that examined children’s physical activity, outdoor time, screen time and social media use during the pandemic lockdown in early 2020 found that 8-year-olds spent an average of more than five hours a day on screens for leisure, in addition to screen time needed for schoolwork.
This report and a new study of school-age children in China after five months of covid-19 home confinement informed the title
of an editorial, “2020 as the Year of Quarantine Myopia,” in the Jan. 14 issue of JAMA Ophthalmology.
Researchers from Emory University in Atlanta, the University of Michigan at Ann Arbor and Tianjin Medical University Eye Hospital in Tianjin, China, described a substantial decline in visual acuity among 123,535 elementary school children following school closures from January to June 2020.
Compared to the results of earlier annual screenings, the ability to see distant objects clearly had fallen precipitously, especially among those ages 6 to 8. The children became far more myopic than expected, based on changes in acuity that were measured at the start of the school years 2015 through 2019. But a similarly dramatic drop in acuity among older children was not found.
LACK OF EXPOSURE
“Given the fact that the younger children were assigned fewer online learning tasks than the older ones, it is unlikely that rapidly progressing myopia in younger children was caused by more intense screen time or near work,” like reading, typing, doing homework or playing video games, the research team wrote in JAMA Ophthalmology. Rather, a lack of exposure to outdoor light is the more likely explanation.
As the editorial writers from Erasmus University Medical Center in the Netherlands suggested, “young children may be more sensitive to myopic triggers from the environment.”
An earlier eye study among children in Sydney also found that only the younger ones who became myopic had spent more time on work rather than being out in daylight.
Although it’s an old theory that excessive reading fosters nearsightedness in children, current thinking is that too much time spent indoors has the greater effect and likely accounts for any apparent association between close work or screen time and myopia.
EYE-SHAPING LIGHT
Dr. Neil M. Bressler, an ophthalmologist affiliated with Johns Hopkins Medical Institutions, said that the high intensity of outdoor light has an important influence on the shape of the eye, which in turn affects whether images are seen clearly.
To be in focus, light rays from an image have to converge on the retina. In myopic eyes, the convergence occurs in front of the retina, and a corrective lens is needed to redirect incoming rays so that distant objects are in focus.
Most children are born slightly farsighted. Their eyes are shaped like partly deflated balls, causing images to converge behind the retina. But as they get older, their eyes elongate to form a sphere, permitting images to converge directly on the retina. However, if elongation fails to stop at some point, the eyes become more oval and images then converge in front of the retina, the definition of myopia.
Outdoor light stimulates the release of dopamine that can slow elongation of the eye, Bressler said.
WORLDWIDE INCIDENCE
Although the rise of myopia is happening worldwide, the incidence is highest in eastern and Southeast Asia, where 80% to 90% of current high school children are myopic.
Concern over the increasing prevalence of myopia goes beyond a growing need for glasses, contact lenses or, for those so inclined and who can afford it, laser treatment to redirect images by changing the shape of the cornea. In general, people with myopia are more likely to develop sight-threatening complications later in life like cataracts, glaucoma and degeneration of the macula, the center of the retina.
If myopia becomes extreme, Bressler said, “it can be tough to correct.” The eye becomes stretched, the retina can spread and form scar tissue and the gel in the center of the eye can become stuck to the sides of the eye, causing retinal tears or detachment, he explained.
“The pandemic has put fuel on the fire,” Bressler said, “but we don’t have a treatment yet.” Currently, the most effective prevention may be for young children to spend less time on screens and a lot more time outdoors.