What is a Retinal Vein Occlusion?

The retina has two blood supplies.  The first is under the retina called the choroid.  The second, is a large artery (central retinal artery) and a large vein (central retinal vein) in the center of the optic nerve.  The artery has high blood pressure and a thick muscular wall, while the vein has low blood pressure and a thin wall. The retinal vessels branch multiple times, and the arteries and vein cross each other multiple times.  Where the arteries cross the veins the artery can squeeze the vein, like a garden hose, causing a clot to form.  This clot blocks the vein causing blood and fluid to build up behind the clot.  This results in swelling in the center of the retina (macular edema), poor blood flow impairing the delivery of oxygen and nutrients to the retina, and sometimes new abnormal blood vessel growth.  Patients may lose vision due to macular edema, blood filling the eye (vitreous hemorrhages), high eye pressure (glaucoma), or tractional retinal detachments.  Injections, laser, and vitrectomy surgery are used to improve vision and prevent further vision loss.