It seems that birth order matters indeed. A new study suggests that first-born children are likely to suffer nearsightedness compared to their younger siblings.
Nearsightedness also known as myopia is increasing in the younger generation, researchers said. Myopia is a growing concern among developing countries including India and China where childhood nearsightedness have skyrocketed in the past years, TIME has learned.
This condition is important because it can cause visual impairment and blindness either directly through myopic chorioretinal atrophy or indirectly through a predisposition to cataract, glaucoma and retinal detachment, Medical News Today, reports.
The study used the data from the British Biobank longitudinal survey to get information from almost 90,000 adults ages between 40 and 69. The researchers combined demographic data with behavioral information. The sample was asked how many times they spend outdoors, along with their detailed educational history and opthalmological past.
The researchers learned that first-born individuals were about 10 percent more likely to be myopic than later-born individuals. Moreover, first-borns were 20 percent more likely to acquire high myopia- a more severe form.
It was previously reported that parents usually spend more on resources for their first-born children resulting in better educational achievements compared to their younger siblings. The study authors associate nearsightedness with the children's education.
According to the report when a couple has their firstborn, they tend to provide the best for their child. Their willingness to be a good provider as well as the cultural preferences for firstborns trigger parents to give their children access to book, iPads, chalkboards, or toys in school which could strain their child's eye.
"My assumption is that individuals who go on to spend more years in full-time education spend relatively less time outdoors and relatively more time in tasks such as reading during their childhood," said Jeremy Guggenheim, a professor of optometry and vision sciences at Cardiff University's Eye Clinic and lead author of the study.
The report suggests that spending more time outdoors reduces nearsightedness rates.
Guggenheim and his team of researchers did not think that there was a possible association between birth order and myopia to educational investment at first.
"To be honest, the relationship with birth order interested us because it seemed a little quirky," he said. "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."
The study was published in JAMA Ophthalmology.
