BACKGROUND: The retinal microvasculature provides a window into cardiovascular health. Retinal microvascular measures derived from fundus photos have previously been linked to several cardiovascular risk factors and are associated with cardiovascular morbidity and mortality. However, little is known on the associations between long-term levels of cardiovascular risk factors and microvascular structure, and the effect of early-life diet on the microvasculature remains unknown. AIM: The aim of this thesis was to study the associations of long-term cumulative cardiovascular risk factor levels and the effects of the randomized dietary counselling intervention on retinal microvascular measures. PARTICIPANTS AND METHODS: The present thesis is part of the randomized Special Turku Coronary Risk Factor Intervention Project (STRIP) and the Cardiovascular Risk in Young Finns Study (YFS). Cardiovascular risk factor levels were measured repeatedly for 26 years in STRIP and for 31 years in YFS. In STRIP, repeated dietary counselling continued from age 7 months until age 20 years. Retinal fundus photographs were taken in young (STRIP, age 26 years) and mid-adulthood (YFS, age 34-49 years), and retinal microvascular measures were derived in both cohorts. RESULTS: Several cumulative cardiovascular risk factors were associated with retinal microvascular measures; for example, higher systolic blood pressure was associated with decreased arteriolar diameter and fractal dimension, higher insulin levels with narrower arteriolar diameter and higher C-reactive protein (CRP) levels with wider venular diameter. Furthermore, the randomized 20-year infancy-onset STRIP dietary counselling intervention had a favorable effect on the retinal microvasculature, resulting in less tortuous arterioles and venules, and increased arteriolar fractal dimension.