A retinal vein occlusion can occur in either the central retinal vein or a branch retinal vein, where a blockage or pressure from a neighboring hardened artery leads to elevated venous pressure. This pressure damages the vein and results in retinal hemorrhages, swelling, and ischemia-a lack of oxygen-in the affected area of the retina. Retinal vein occlusion occurs equally in men and women, most commonly after the age of 60. It is more likely to occur in patients with diabetes, hypertension, or cardiovascular disease.

Patients typically experience a sudden onset of blurred vision or a "missing area" in their visual field when a branch retinal vein is affected. If the central retinal vein is occluded, the result is often a more severe loss of central vision.