The retina, a window of cerebrovascular disease in diabetes

Abstract

Cerebrovascular disease is one of the complications of long-term diabetes mellitus. While the structure and function of the great cerebral vessels may be more easily studied, the cerebral microcirculation is difficult to assess. However, a simple eye fundus examination with an ophthalmoscope enables to visualize the microvascular abnormalities that characterize diabetic retinopathy, which isth e most common microvascular complication of diabetes. The anatomical and functional similarity between retinal and cerebral microcirculation supports the hypothesis that alterations in retinal vascular reactivity could be considered as an early marker of cerebral microvascular dysfunction in diabetes. The initiating factor of diabetic angiopathies is endothelial dysfunction. Endothelial dysfunction results in a reduced bioavailability of nitric oxide (NO), as a consequence of decreased NO synthesis and/or increased production of free oxygen radicals that are NO scavengers. Diabetes also stimulates the production of endothelial-derived contractile factors such as superoxide anions and hydroxyl radicals, endothelin and certain cyclooxygenase (COX) derivatives. COX activation is related to a high level of oxidative stress. Oxidative stress participates in the inflammatory response involved in the diabetic vascular dysfunction. These pathogenic mechanisms have been shown in both cerebral and retinal arteries, mainly through in vitro vascular reactivity studies, suggesting that diabetes induces a profound change in microvascular regulatory mechanisms. The association between the degree of retinal perfusion, brain injuries and altered cognitive function indicates a certain parallelism in the degree of impairment of both retinal and brain circulations. In addition, prospective studies conclude that diabetic retinopathy predicts ischemic cerebrovascular disease independently of other risk factors, supporting the importance of cerebral microvascular disease in diabetics. Further research on the vascular abnormalities is needed to understand the pathogenic mechanisms underlying retinopathies and cerebrovascular disease in diabetes. In the near future, the use of fully automated methods to detect signs of retinopathy will not only facilitate the efficient evaluation of vascular changes in the retina but will also help to reduce cerebral vascular morbidity and mortality.