Diameters of retinal arterioles and venules measured from digitised photographs of the retina taken at baseline. Measurements summarised as the arteriole:venule ratio, with a lower ratio indicating smaller arteriolar diameters. Incident hypertension, defined as systolic blood pressure =140 mm Hg, diastolic blood pressure =90 mm Hg, or use of antihypertensive drugs during follow up.