Aims To investigate the independent associations between metabolic syndrome and retinal vessel calibre in a high cardiovascular risk cohort, and to determine whether these associations also exist in patients without diabetes, hypertension or coronary artery disease (CAD).

Methods The Australian Heart Eye Study is an observational study that surveyed 1680 participants who presented to a tertiary referral hospital for the evaluation of potential CAD by coronary angiography. Metabolic syndrome was defined according to the Third Report of the National Cholesterol Education Program. Retinal arteriolar calibre narrowing and retinal venular calibre widening were measured from retinal photographs. CAD was quantified using severity (Gensini) and extent scores. Diabetes and hypertension were defined from clinical investigation (fasting plasma glucose >7.0 mmol/L and blood pressure >130/85 mm Hg) or from self-reported clinical diagnosis, including the use of medications.

Results A total of 979 participants had complete information on metabolic syndrome components and were included in cross-sectional analyses. After adjusting for age, sex, smoking status and fellow vessel calibre, persons with metabolic syndrome (compared with persons without metabolic syndrome) had narrower retinal arteriolar calibre (mean difference 4.3 µm, p<0.0001). No significant difference in venular calibre was observed (p=0.05). This association persisted in persons without diabetes (mean arteriolar calibre difference 4.4 µm, p=0.0006) but not in participants without CAD and those without hypertension.

Conclusions Metabolic syndrome is independently associated with narrower retinal arterioles but not wider retinal venules among those at high risk of CAD. The association between metabolic syndrome and narrower retinal arterioles is likely due to the presence of CAD or hypertension in individuals with this syndrome, as the association is not significant in individuals without hypertension or without CAD.