Researchers have explained why first-born children are more likely to be myopic than their younger siblings. The findings are published in JAMA Ophthalmology.
Myopia is becoming more and more common in our contemporary world. Previous studies have suggested that first-born children might have a greater risk of becoming near-sighted. This study explains how this happens.
Jeremy A. Gugenhenheim, from Cardiff University, and his team hypothesised that the cause might be linked with educational investment. Other studies indicate that parents have the propensity to invest more resources in their first-borns such that the latter have better academic performances than the younger children. Parents would, in this manner, provide a “myopia-predisposing environment”. The researchers aimed to find out whether this is true.
Data from over 89,000 UK Biobank participants aged between 40 and 69 years old who were previously subjected to a vision assessment and had no history of eye disorders was analysed.
The results show that first-borns are 10 % more likely than younger siblings to be myopic. They were also 20 % more likely to have high myopia which is a more severe form of the condition.
The findings also suggest that parents investing fewer resources in the younger children’s education might also account for the trend.
“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,” write the authors.
However, the researchers cautioned that education and myopia might not necessarily be linked, saying that “a causal relationship cannot be confirmed using observational data.”
The researchers add that their findings “suggest that the association between birth order and myopia is not due to a new environmental pressure in the last 30-40 years” and “supports a role for reduced parental investment in education of children with later birth orders in their relative protection from myopia.”