Retinal vascular caliber measurements: clinical significance, current knowledge and future perspectives.

The retinal vasculature provides a unique window to assess vascular health noninvasively and directly in vivo. Advances in fundus photography and retinal image analysis techniques have enabled the objective and accurate assessment of quantitative retinal vascular caliber measurement. Over the last decade, large population-based studies have shown that retinal vascular calibers are associated with a wide range of subclinical (e.g. atherosclerosis, inflammation and endothelial dysfunction) and clinical cardiovascular diseases (hypertension, diabetes mellitus, stroke, kidney and heart diseases). However, while retinal image analysis provided exciting possibilities to study the pathogenesis of these diseases, its direct applicability in a clinical setting as a 'test' to predict cardiovascular diseases is yet to be established, particularly within the context of being used as a population screening tool. Nevertheless, with continual development of retinal imaging techniques and newer understanding of the clinical significance of these retinal changes, there remains scope for the development of retinal vascular caliber measurements as a biomarker for vascular disease risk assessment in targeted areas and patient subgroups (e.g. patients with diabetes, suspected hypertension and stroke).