Structural and hemodynamic analysis of the mouse retinal microcirculation

PURPOSE. In the holangiotic retina, little is known about the connections between and the circulation within microvessel layers. The goal of the present study was to explore the three-dimensional arrangement and hemodynamics of mouse retinal microvessels. METHODS. Confocal microscopy was performed on fluorescein dextran-filled retinal flatmounts. Capillary velocity in the deep layer was measured by epifluorescence intravital microscopy. The changes in the studied parameters after branch retinal vein occlusion were evaluated. RESULTS. The superficial and intermediate layers are both asymmetric crossroads for capillary blood flow, with approximately 70% of the capillary connections directing the flow from the arterioles into the deep layer. The venous flow from the deep layer joins the major veins in the superficial layer through transverse venules, indicating that major veins are directly connected to the deep layer. Red and white blood cell velocities +/- SD in the deep layer were 1.26 +/- 0.34 and 0.8 +/- 0.32 mm/sec respectively. After branch vein occlusion, venule dilation and decreased velocity were observed in the deep layer. CONCLUSIONS. In the mouse retina, a tridimensional model of retinal microcirculation was established, showing that most microvessel connections on the arteriolar side direct the flow from the superficial to the deep layer, and vice versa on the venular side. However, the presence of direct arteriovenous connections in the superficial layer and the longer vessel length in the deep layer offer the possibility of actively modulating intraretinal flow. Compared with other capillary beds, both the capillary velocity and microhematocrit are high, a situation that favors nutrient delivery to the inner retina.