Central Retinal Vein Occlusion - Nonischemic with Watershed Zone Ischemic Retinal Whitening
The retina is supplied by end arterioles. This means that there is no overlap in the circulatory supply to the retina. For this reason, watershed zones (zones at the juncture of regions supplied by different arterioles) are the most sensitive to inadequate oxygenation. This picture shows a consequence of this arrangement. The white zone marked by the arrows is a watershed zone between the inferotemporal and superotemporal retina. The oxygen in the blood has been extracted to the greatest extent in this zone, and in the circumstance of a central retinal vein occlusion, as has happened here, the oxygen level is insufficient to support retinal metabolism. As a result the retina turns milky. Transparency of the retina is an indicator of adequate oxygenation.