Studies on the angioarchitecture of the posterior choroid in rat and role of posterior ciliary vein.

Vascular casts were made by injection of low-viscosity plastic in eight Wistar-Kyoto rats, and the posterior half of the ocular wall was observed using the semiultrathin section method. Veins which connect with the capillaries of the posterior choroid include a venous system independent of the cortex vein and running parallel to the long and short posterior ciliary arteries. The veins flow into a venous ring which is located in the region at which the arterial circle of Zinn is said to be. There was no structure in this region which could be described as an arterial circle. From the above findings, it is concluded that these venous systems are part of the posterior ciliary vein and that they play an important role as a pathway for irrigation of blood from the posterior choroid.