Impact of retinal vascular tortuosity on retinal circulation

The retinal microvasculature is a window to the systemic circulation. Systemic diseases, like diabetes and hypertension, are linked to retinal microvascular structure changes (as width, tortuosity, and branching angle). The latter results in a potentially disadvantageous blood flow. This study has been designed to examine the relationship of a retinal vascular tortuosity to both blood pressure and velocity. The geometrical outlines of realistic retinal vascular trees have been extracted from fundus images. The retinal venular tortuosity has been quantitatively measured. A normal tortuosity value has been found, which has not exceeded 1.2. A computational fluid dynamics study has been conducted to examine the effect of topological changes on the hemodynamics distribution in the retinal circulation. The microvascular diameter effect (i.e., Fahraeus–Lindqvist effect) and the hematocrit have been considered in determining the viscosity of the blood in the retinal vessel segments. The pressure drop and the maximum velocity have been in the order of 15 mmHg and 0.032 m/s for tortuous vessels, and 13 mmHg and 0.054 m/s for normal vessels, respectively. For a clinical case, the maximal velocity falls down to 14 % due to the tortuosity. The current results have shown a decrease in the blood velocity and an increase in the pressure drop with tortuosity, which are in good agreement with in vivo measurements reported in the literature.