A disruption to normal blood flow through your retinal vein causes this condition. The disruption may happen due to:
- A blood clot.
- A slowdown of blood flow.
- Compression of your retinal vein at the point where it crosses paths with your retinal artery. Your retinal artery supplies oxygen-rich blood to your retina. Your retinal artery may grow stiff from aging or plaque buildup, and it may press on your retinal vein. This can damage the inner lining of your retinal vein, creating conditions where a blood clot is more likely to form.