Quantification of retinal capillary density and flow velocity in patients with essential hypertension.

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Abstract
Arterial hypertension is known to be an important risk factor for cerebral and cardiovascular disease. Previous studies in rats have demonstrated that changes in both capillary density and vessel diameter may contribute to increased vascular resistance in hypertension. In vivo studies of human subjects with essential hypertension revealed a reduction in the number of arterioles in the skin and conjunctiva; no other in vivo data are available from other tissues. By means of a new imaging technique, capillary density and capillary blood flow velocity can now be assessed in the human retina. We undertook the present investigation to determine whether patients with essential hypertension and only minor clinical retinal vascular alterations have decreased retinal capillary density and altered capillary flow velocity. Seventeen hypertensive patients with only minor retinal vascular alterations and 17 healthy volunteers matched for age were selected. All study participants underwent ophthalmologic examination and fluorescein angiographic studies by means of scanning laser ophthalmoscopy. Capillary density and capillary blood flow velocity in the perifoveal network were evaluated from the angiograms. The retinal microcirculation in the perifoveal capillary network of hypertensive patients showed significant alterations. Both the capillary density and capillary flow velocities were significantly reduced compared with the control group. For the first time alterations of capillary blood flow and capillary density in a vascular network very similar to that of the brain have been demonstrated in hypertensive patients in vivo. Further studies with this technique may help identify patients at high risk for cerebrovascular diseases.