PURPOSE. We describe the profile and associations of anisometropia and aniso-astigmatism in a population-based sample of children. METHODS. The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit a representative sample of children from schools in Northern Ireland. Examinations included cycloplegic (1% cyclopentolate) autorefraction, and measures of axial length, anterior chamber depth, and corneal curvature. v 2 tests were used to

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... ess variations in the prevalence of anisometropia and anisoastigmatism by age group, with logistic regression used to compare odds of anisometropia and aniso-astigmatism with refractive status (myopia, emmetropia, hyperopia). The Mann-Whitney U test was used to examine interocular differences in ocular biometry. RESULTS. Data from 661 white children aged 12 to 13 years (50.5% male) and 389 white children aged 6 to 7 years (49.6% male) are presented. The prevalence of anisometropia ‡1 diopters sphere (DS) did not differ statistically significantly between 6-to 7-year-old (8.5%; 95% confidence interval [CI], 3.9-13.1) and 12-to 13-year-old (9.4%; 95% CI, 5.9-12.9) children. The prevalence of aniso-astigmatism ‡1 diopters cylinder (DC) did not vary statistically significantly between 6-to 7-year-old (7.7%; 95% CI, 4.3-11.2) and 12-to 13-year-old (5.6%; 95% CI, 0.5-8.1) children. Anisometropia and aniso-astigmatism were more common in 12-to 13-yearold children with hyperopia ‡þ2 DS. Anisometropic eyes had greater axial length asymmetry than nonanisometropic eyes. Aniso-astigmatic eyes were more asymmetric in axial length and corneal astigmatism than eyes without anisoastigmatism. CONCLUSIONS. In this population, there is a high prevalence of axial anisometropia and corneal/axial aniso-astigmatism, associated with hyperopia, but whether these relations are causal is unclear. Further work is required to clarify the developmental mechanism behind these associations. (Invest Ophthalmol Vis Sci. 2013;54:602-608)