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(Hypertension. 2009;53:487.)
© 2009 American Heart Association, Inc.

Original Articles

Effect of Birth Parameters on Retinal Vascular Caliber

The Twins Eye Study in Tasmania

Cong Sun; Anne-Louise Ponsonby; Tien Y. Wong; Shayne A. Brown; Lisa S. Kearns; Jenny Cochrane; Jane R. MacKinnon; Jonathan B. Ruddle; Alex W. Hewitt; Gerald Liew; Terence Dwyer; Katrina Scurrah; David A. Mackey

From the Centre for Eye Research Australia (C.S., T.Y.W., L.S.K., J.B.R., A.W.H., D.A.M.), Murdoch Children’s Research Institute (A.-L.P., T.D., D.A.M.), Centre for Molecular, Environmental, Genetic and Analytic Epidemiology (K.S.), and Department of Physiology (K.S.), University of Melbourne, Melbourne, Australia; Menzies Institute (A.-L.P., S.A.B., J.C., T.D.), University of Tasmania, Tasmania, Australia; Singapore Eye Research Institute (T.Y.W.), National University of Singapore, Singapore; Ocular Diagnostic Clinic (L.S.K., J.B.R., D.A.M.), Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia; Department of Ophthalmology (L.S.K., D.A.M.), Royal Children’s Hospital, Melbourne, Australia; Department of Ophthalmology (J.R.M.), Royal Hospital for Sick Children, Glasgow, United Kingdom; and Centre for Vision Research (G.L.), University of Sydney, Sydney, New South Wales, Australia.

Correspondence to David A. Mackey, Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, VIC 3002, Australia. E-mail D.Mackey{at}utas.edu.au

Recent studies reported an association between smaller birth size and narrower retinal vascular caliber, but it remains unclear whether this association is attributed to confounding by shared environment or genetic factors. At a mean age of 9.3 years, 266 twins (49 monozygotic and 84 dizygotic pairs) in the Twins Eye Study in Tasmania underwent an ophthalmic examination including retinal photography. Retinal vascular caliber was measured using a validated protocol. The majority of these twins were also in the Tasmanian Infant Health Study, which prospectively collected data on birth parameters and antenatal maternal factors. We conducted the main analysis using linear mixed models, accounting for birth set clustering. Both the within-pair (–9.73; 95% CI: –14.68 to –4.77 µm per 5-cm decrease in birth length) and between-pair associations (–7.15; 95% CI: –11.54 to –3.01) with retinal arteriolar caliber were significant and of similar magnitude (difference in effect, P=0.61), after adjusting for age, sex, maternal smoking, mean arterial blood pressure, and other confounders. These associations remained within dizygotic and monozygotic pairs. Analyses of head circumference and retinal arteriolar caliber were similar to those of birth length (within-pair regression coefficient: –2.41; 95% CI: –5.09 to 0.28; between-pair regression coefficient: –2.60; 95% CI: –5.00 to –0.19). For birth weight, only a between-pair association was evident (–7.28; 95% CI: –13.07 to –1.48). This study demonstrates a consistent association between smaller birth size and narrower retinal arterioles in twins. The independent effect of shorter birth length on retinal arteriolar caliber supports a role for twin-specific supply line factors affecting fetal growth on vascular structure.

Key Words: twins • epidemiology • blood pressure • arterioles • birth weight • birth length • head circumference

This article has been cited by other articles:

				C. Sun, G. Zhu, T. Y. Wong, A. W. Hewitt, J. B. Ruddle, L. Hodgson, G. W. Montgomery, T. L. Young, C. J. Hammond, J. E. Craig, et al. Quantitative Genetic Analysis of the Retinal Vascular Caliber: The Australian Twins Eye Study Hypertension, October 1, 2009; 54(4): 788 - 795. [Abstract] [Full Text] [PDF]

				N. Cheung Birth Factors and Retinal Vascular Caliber in a Twin Study Hypertension, April 1, 2009; 53(4): e28 - e28. [Full Text] [PDF]