Only rarely is vascular occlusion of the choroid a clinically significant problem. This system is highly vulnerable to occlusion because it is an end-artery system. Pathophysiology of occlusion Either the retinal vein or the retinal artery can become occluded, as can the central retinal vein or artery. An arteriole crossing a vein compresses the vein, causing stagnation of blood flow. A thrombus forms, leading to either partial or complete obstruction.
Back pressure generated behind the area of occlusion causes extravasation of blood into the retina.
The blood dissects the retinal tissue, resulting in mechanical distortion. When embolic occlusion occurs, the change in visual function is immediate. The normally homogeneous and transparent retina thickens and becomes opaque in the ischemic region. These changes are irreversible unless the embolus can be dislocated to a more distal position. The most common types of retinal vascular occlusive disease are central retinal vein occlusion, branch retinal vein occlusion, and central retinal artery occlusion.