Purpose: To examine the relationship of birth weight with ocular measures in a Caucasian twin population.
Design: Cross-sectional study of 1498 twins (308 monozygotic and 441 dizygotic pairs) aged between 5 to 80 years participating in the Australian Twins Eye Study.
Methods: All participants underwent ophthalmic examination including bilateral cycloplegic autorefraction, keratometry, interpupillary distance (IPD), central corneal thickness, intraocular pressure (IOP), and retinal photography. Birth weight and gestation were obtained from a self-administered questionnaire. A subset of the twins also participated in the Tasmanian Infant Health Study (288) and the Childhood Blood Pressure Study (184), which collected data on birth parameters allowing for verification of data. Linear mixed models were used for the main analysis.
Results: Both the within-pair (β(w) 0.27, 95% confidence interval [CI] 0.15, 0.38 mm per kg increase in birth weight, P < .001) and between-pair associations (β(B) 0.22, 95% CI 0.08, 0.35, P = .002) of birth weight with axial length were significant and of similar magnitude (difference in effect, P = .56), after adjusting for relevant confounders. In contrast, birth weight was negatively associated with corneal curvature (β(w) -0.82, 95% CI -1.09, -0.55 diopters per kg increase; β(B) -0.69, 95% CI -0.98, -0.41, both P < .001). These associations remained significant within dizygotic and monozygotic pairs. Refraction, anterior chamber depth, IPD, IOP, and optic disc parameters are unrelated to birth weight.
Conclusions: Consistent with previous studies in singleton children, lower birth weight is associated with shorter axial length and more curved corneas in this twin study. This also adds new insights into the emmetropization process.
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