Children without siblings tend to spend more time doing near vision activities, which may be why this study found them to be at an increased risk for myopia. Photo: Getty Images.

New research further elucidates the connection myopia may have with the number of kids in a family. The prospective, cross-sectional study specifically aimed to see if differences in optical axial length and close work activities are present amongst only children and those with siblings. 

The study—including 2,913 children—collected data about optical axial length, spherical equivalent refraction, the number of children in the family, parental myopia and close work activities. Data was collected through means of eye examinations and questionnaires. 

Results found that only children were 1.2-times more likely to display an axial length greater than 24mm compared to children with siblings. As such, 44.5% of only children displayed an axial length greater than 24mm, while only 35.6% of children with siblings did. The percentage of all children with this axial length lies between these two categories at 38.9%. Actual prevalence of myopia was 46.7% amongst only children and 46.0% amongst multiple children. 

Researchers not only found a difference in axial length but in behavior too, as it relates to school activities. Only children were found to be 1.3-times more likely to spend more than one hour on homework on the weekends compared to children with siblings. This becomes even more pronounced in only children in upper grades, found to be 1.5-times more likely to spend greater than an hour on homework on weekends. Additionally, boys who also happened to be only children were found more likely to attend three or more extracurricular classes for academics. 

The researchers believe higher instances of myopia and an increasing prevalence may be in part caused by the family environment, often pushing increased educational pressure on only children. This is somewhat reflective of previous research that has found only children spend 0.6 hours more on homework a day than children with siblings, and this was consistent with the findings of the current study. Interestingly, the only children of this study were found to participate in more writing time—but used electronics less. This again is likely due to the environment parents are adopting in mediating their only child’s close work activities. 

Based on the findings of the study, the authors recommend that “schools and parents give their children more opportunities to engage in outdoor activities to reduce the pressure and burden of schoolwork, and boys are encouraged to participate in more outdoor training.” It’s one thing to tell parents to be aware of this, but the authors also comment that clinicians and researchers “should pay more attention to this high-risk group in future myopia prevention and control” and “pay more attention to the visual health of only children.”

Wang Y, Lin Y, Jiang D, et al. Differences in close-work activities and optical axis length between only children and non-only children: a cross-sectional study. BMC Ped. 2022. [Epub ahead of print].