IMPORTANCE: Intraocular pressure (IOP) is the principal modifiable risk factor for the progression of primary open-angle glaucoma. Studies that have measured the IOP directly in large numbers of matched parent-offspring pairs are limited in Asian populations. OBJECTIVE: To compare IOPs in parents and their offspring in Korea. DESIGN, SETTING, AND PARTICIPANTS: Family-based cohort study examining data from the Korean National Health and Nutrition Examination Survey conducted between 2008 and 2009. Data were obtained from 9700 participants from Korea. MAIN OUTCOMES AND MEASURES: Familial correlations for IOP were calculated in different types of relative pairs. Variance component methods were used to obtain heritability estimates. The individuals were stratified into 2 groups (those with and those without an IOP of ≥19 mm Hg; ie, high IOP group and nonhigh IOP group) based on the mean plus 2 SD IOP value of the entire study population. We evaluated the impact of parents' high IOP on offspring's high IOP. The relationship between parental systemic disease and high IOP in their offspring was also investigated. RESULTS: The mean (SD) IOPs in the right and left eyes were 13.90 (2.74) and 13.89 (2.74) mm Hg, respectively. Correlation coefficient estimates between parent-offspring pairs, sibling pairs, and spouse pairs for IOP were significant as 0.19, 0.31, and 0.29 (P < .001, P = .001, and P < .001, respectively). The total variance of the phenotype under study was explained by 2 sources of variation, additive genetic (36% [95%CI, 32%-40%]) and unique environment (64% [95%CI, 60%-68%]). The risks of high IOP conferred by parents' high IOP were found to be significant for participants whose parents had high IOP (odds ratio, 9.76 [95%CI, 2.16-44.12]). In this study, high IOP was not associated with parental diabetes mellitus, hypertension, obesity, or metabolic syndrome. CONCLUSIONS AND RELEVANCE: Intraocular pressure showed a significant heritable tendency from parents to their offspring with a heritability estimate of 0.36 in Asian populations. The risk of high IOP was significantly increased in participants whose parents had high IOP. This has potential implications for the screening of family members of patients with ocular hypertension and glaucoma.
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