Body Roundness Index and Reported Vision Difficulty in U.S. Children and Adolescents: A Cross-Sectional Study of NHANES 2021–2023

Background: Vision difficulty (VD) in childhood and adolescence may affect learning, daily functioning, and quality of life. Although body roundness index (BRI) has emerged as an indicator of central adiposity and cardiometabolic risk, its association with reported VD in pediatric populations remains unclear. Methods: We conducted a cross-sectional analysis using data from the National Health and Nutrition Examination Survey (NHANES) August 2021–August 2023. Participants aged 5–17 years with available data on VD, BRI, and covariates were included. VD was defined as self- or proxy-reported difficulty seeing even when wearing glasses or contact lenses. Survey-weighted logistic regression models were used to examine the association between BRI and VD, with progressive adjustment for demographic, socioeconomic, and lifestyle factors. BRI was analyzed as both a continuous variable and weighted quartiles. Restricted cubic spline (RCS) analysis was performed to assess the dose–response relationship. Results: A total of 1566 participants were included. In the fully adjusted model, each one-unit increase in BRI was associated with 12% higher odds of VD (odds ratio [OR] = 1.12, 95% confidence interval [CI]: 1.02–1.23, p = 0.029). Per 1 standard deviation increase in BRI, the OR for VD was 1.20 (95% CI: 1.03–1.40). Weighted quartile analysis showed imprecise fully adjusted estimates; descriptively, weighted VD prevalence was higher in the highest than in the lowest BRI quartile. RCS analysis showed a significant overall association (p-overall = 0.0297) without evidence of non-linearity (p-non-linearity = 0.861). Conclusions: Higher BRI was associated with greater odds of reported VD among U.S. children and adolescents. Given the cross-sectional design and questionnaire-based outcome, these findings should be interpreted as a population-level association rather than evidence of causality or clinical utility.