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Study Finds First-Borns in the Family Are More Likely to Be Nearsighted — Here's One Thought Why

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"It seemed a little quirky."

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Are you a first born? If so, do you find yourself reaching for a set of glasses or relying on contacts to see things that are far away?

A study published in the JAMA Ophthalmology this week found that from its sample of over 89,000 people 40 to 69 years old in the U.K., those who were first-borns were 10 percent more likely to be nearsighted — able to see objects close up but cannot clearly see things further away — compared to their later-born sibling.

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This, the study authors suggested, could be, in part, because parents might put more emphasis on school work for older siblings than for younger.

The researchers found that first-borns were 10 percent more likely to have myopia (the scientific term for nearsightedness) and 20 percent more likely to have severe myopia than later-borns.

According to the American Optometric Association, there is evidence that nearsightedness can be influenced by genetics, but environmental and health factors come into play as well.

"Even though the tendency to develop nearsightedness may be inherited, its actual development may be affected by how a person uses his or her eyes," AOA stated on its website. "Individuals who spend considerable time reading, working at a computer,or doing other intense close visual work may be more likely to develop nearsightedness."

When the investigators adjusted for education — determined as the highest educational level reached or the age at which full-time education was completed — they found this factor seemed to account about 25 percent of the relationship between birth order and the likelihood of being nearsighted.

"Greater educational exposure in earlier-born children may expose them to a more myopiagenic [factors causing myopia] environment; for example, more time doing near work and less time spent outdoors," the study authors wrote. "Our findings that statistical adjustment for indices of educational exposure partially attenuated the magnitude of the association between birth order and myopia, and completely removed the evidence for a dose-response relationship, therefore support the idea that reduced parental investment in children's education for offspring of later birth order contributed to the observed birth order vs myopia association and produced the observed dose-response relationship."

Though this observation was made, the study authors wrote that it doesn't necessarily confirm as casual relationship.

“To be honest, the relationship with birth order interested us because it seemed a little quirky,” Jeremy Guggenheim, a professor of optometry and vision sciences at Cardiff University and lead author of the study, told Time. “Scientists are always very careful not to presume causality when they see a correlation, but then again, if a correlation keeps appearing then it must have a cause, even if the cause is indirect.”

Nearsightedness in children has become a growing problem. According to an article published in Nature earlier this year, 90 percent of teens and young adults in China are short-sighted, up from only 10 to 20 percent 60 years ago. Myopia in the teens in the U.S. and other developed countries ranges between 25-35 percent, according to the AOA.

A study published last month in the Journal of the American Medical Association found that children in China who received an additional 40 minutes of time outside in school reduced incidents of nearsightedness over a three-year period.

Front page image via Shutterstock.

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