Retinal vein occlusions are classified as central retinal vein occlusion (CRVO) if the blockage occurs in the main vein leaving the eye through the optic nerve They are classified as branch retinal vein occlusion (BRVO) if the blockage occurs at one of the branches before reaching the main vein at the nerve; these often occur where arteries and veins cross. When patients have a retinal vein occlusion, they frequently complain of blurred vision, distortion, and/or a central blind spot.

Occluded veins typically appear tortuous, just as a hose tends to twist when water flow is blocked. There is bleeding seen in the distribution of the blocked vein in BRVO; the whole retina is involved in CRVO. There is also usually swelling of the retina in the same distribution; macular edema is a common finding and is often a source of significant visual loss. When there is a severe blockage in which blood flow is cut off or significantly reduced, sensitive retinal tissue can become permanently damaged. This process is called ischemia. As a response to ischemia, the eye may develop abnormal new blood vessels called neovascularization. Unfortunately, these new vessels are fragile and tend to bleed, potentially resulting in vitreous hemorrhage. They may also scar and pull on the retina, potentially resulting in traction retinal detachment. Finally, if these blood vessels grow in the drainage structure of the eye, a very serious form of glaucoma can develop called neovascular glaucoma.