Results from the Nationwide German KiGGS Study in Children and Adolescents Show that Myopia is Associated with Being an Only Child.

Purpose: Several studies suggest that myopia is more frequently observed in first-born compared to later-born children. However, it is unknown whether the prevalence of myopia in alpha birth order differs between only-children and first-borns with siblings.

Methods: In this post-hoc study, we analyzed weighted data from the nationwide, representative German Health Interview and Examination Survey for Children and Adolescents (KiGGS) and assessed the relationship between birth order and the prevalence of refractive anomalies in study participants aged 11-17 years (n = 3,429).

Results: Our results showed that there was a significantly higher percentage of self-reported myopia in only-children as compared to first-borns with siblings (34.5% vs 28.2%, p = 0.001). A logistic regression model with myopia as dependent variable and only-child status as independent variable adjusted to age, sex, body-mass index, socioeconomic and migration status confirmed that only-child status was independently and positively associated with myopia (odds ratio = 1.396, 95%-confidence interval = 1.166-1.671, p < 0.001). However, no such relationship was found for hyperopia (p = 0.203).

Conclusions: Myopia, but not hyperopia, was significantly and positively related to only-child status, irrespective of confounders as age, sex, body-mass index, as well as socioeconomic and migration status. Further research is needed to decipher the pathophysiological mechanisms underlying this relationship.