Figure 1. Murine and rat retinal flat mounts. Flat mounted retinas from mice or rats stained with lectin. The main vessels are arranged
radially with alternating arteries and veins. A: Six arteries (a) are separated by three large and three smaller veins (v) in mice. The two largest veins form three peripheral
arcs draining additionally the peripheral areas of the smaller veins without crossing an artery. Arteriovenous crossings are
highly rare and are not found in most retinas. B: There are some arteriovenous crossings (indicated by green circles) in rats. Most crossings are found at two-thirds the
distance between the optic nerve head and the periphery. Usually, the vein is crossing an artery to reach an area between
two arterial branches or an area between two arteries with a small and short vein in between.