Moreover, the techniques and tools that are currently applied are

Moreover, the techniques and tools that are currently applied are manual or semiautomatic in nature, for

which the observer has an important influence, thus providing limited information. In population studies, an association has been found between the calibre leave a message of the retinal vessels and arterial hypertension,8 left ventricular hypertrophy,9 metabolic syndrome,10 stroke11 and coronary heart disease,12 especially in women.13 However, other studies disagree and show contradictory results regarding the evolution of the arteriosclerotic lesion and the calibre of the retinal vessels.14–16 In this way, Cuspidi et al17 and Masaidi et al18 failed to detect an association between the calibre of the retinal vessels and target organ injuries (cardiac, vascular and renal) in studies of two hypertensive populations. However, Torres et al19 reported a negative association between carotid intima-media thickness (IMT) and the thickness of the retinal arteries but a positive association with the veins. Recently, our group developed and validated a semiautomatic tool, the arteriovenous index calculator, to evaluate the vascular calibre of the retinal vessels,20 with reduced influence of the observer. This tool showed

high reliability when measuring the calibre of the retinal vessels with an intraclass correlation coefficient (ICC) for intraobserver and interobserver greater than 0.96 for veins, arteries and the arteriovenous ratio (AVR). These measures, especially the venous calibre and the AVR, were also shown to be independent variables associated with estimated cardiovascular risk, according to the Framingham scale and the microvascular kidney lesions evaluated according to the level of microalbuminuria. This positive association between the cardiovascular risk and the venous calibre is in line with several published studies showing an association between the AVR and the risk of coronary heart disease.12 13 21 However, longitudinal studies with a

greater number of patients would help to clarify the discrepancies among previously published studies on cardiovascular risk, and vascular structure and function. Moreover, it should not be forgotten that these tools provide less information than GSK-3 retinal imaging on the thickness of the arteries and veins, their branching patterns and the vascularised areas, which may be relevant for evaluating the status of the vascular tree and may be the cause of some of the discrepancies previously reported. A new and different approach to the study of the vascular systems is the characterisation of the blood vessel patterns in the normal circulation of the human retina.22 With this method, the distribution of the branching of the vascular system in a two-dimensional space can be analysed, and the geometrical complexity of the branching and the density of the retinal vessels can be quantified.

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