Retinal vascular imaging in cardiovascular medicine: New tools for an old examination

Abstract

The old concept that the eye is the only window through which the body microcirculation can be observed in life easily, safely and repeatedly is part of the cultural baggage of every physician. When Hermann von Helmholtz invented the direct ophthalmoscope in 1850, he opened the door to a non-invasive visualization of human microcirculation in vivo at the retina. Only a few years later, the Scottish ophthalmologist Marcus Gunn documented the close association between retinal changes, and renal and cardiovascular diseases (CVD) in hypertensive patient. In 1939, Keith, Wagener, and Barker showed that the severity of retinal microvascular abnormalities was predictive of mortality in patients with hypertension. Retinal arterioles have anatomical and physiological similarities with those of the renal, cerebral and coronary circulation, suggesting that retinal microvascular changes may reflect structural and functional damage elsewhere in end-organ tissues [3]. Thus, potentially studying the retina may provide an additional tool for clinicians to better stratify risk and help identify people who would benefit from preventative therapies. However, in the last few decades, there has been less clinical interest in retinal microvascular abnormalities, for a number of reasons. Thanks to the early diagnosis of hypertension and the widespread use of antihypertensive therapy, the more advanced retinal vessel abnormalities described in the pioneering investigation of Keith et al. (e.g., Grade III and IV retinopathy) are nowadays relatively uncommon. Thus, the majority of current hypertensive patients show initial fundal alterations whose prognostic significance is controversial If considered as a proof of target organ damage, these retinal changes would classify most patients in the high-risk category, according to many guidelines on the management of arterial hypertension . Moreover, although it is relatively simple to identify subjects as belonging to grade III or IV hypertensive retinopathy, there are many difficulties in the allocation of subjects into the lower degrees, partly because retinal vessel calibres change frequently with posture, blood pressure level, cardiac cycle and autonomic nervous system activity. Hence, the probability of an observer error is very high. More recently, digitized retinal photography and novel computer-based imaging methods have become accepted as more standardized and objective techniques for characterizing retinal microvascular phenomena.....