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When it comes to studies on birth order, first-borns tend to make out pretty well. Research says they tend to be smarter, more outgoing, and exhibit more leadership qualities.

Unfortunately, it's not all good news. A new paper published in JAMA Ophthalmology shows that first-borns also tend to be 10 percent more likely to be near-sighted and 20 percent more likely to have severe myopia than their siblings. In fact, the risk for myopia appeared to be progressively lower the later you were born in terms of your birth order.

The researchers from Cardiff University suggested that the cause was “parental investment in education” because parents may have a tendency to put more pressure on first-borns. They theorized that parents may be more demanding that first-borns do more "near" activities, such as reading, which may impact their eyesight. Previous studies have shown a strong link between time spent outdoors and a diminished risk of myopia, and it may stand to reason that children who spend more time on studies may be spending less time outdoors.

Jeremy Guggenheim, a doctoral student, and colleagues wrote that while there's no way to make a definitive causal link, their study found that when they adjusted for a proxy for educational exposure — the highest educational degree or age at completion of full-time education — they saw a less dramatic association between near-sightedness and birth order.

"These data suggest that the association between birth order and myopia is not due to a new environmental pressure in the last 30 to 40 years," Guggenheim wrote. "The attenuated effect size after adjusting for educational exposure supports a role for reduced parental investment in education of children with later birth orders in their relative protection from myopia."

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