Choroidoretinal vascular anastomosis.

Vascular anastomoses between the retina and choroid may occur in different congenital and acquired conditions. It has been postulated that the direction of blood flow in these anastomoses follows a pressure gradient characterized as follows: choroidal artery greater than retinal artery greater than retinal vein greater than choroidal vein. Of the four possible directions of blood flow between the two circulations that this theory allows, only three have previously been reported. The fourth, described in this report, is a choroidoretinal vascular anastomosis with blood flow from a choroidal vessel into a retinal vein.