Overview of branch retinal vein occlusion and central retinal vein occlusion.
Arteries bring blood to the eye and veins bring blood back to the heart. While arteries have tough walls which usually become harder with age, veins have thin walls which remain pliant and soft throughout life. Because of the anatomy of the eye, the retinal veins are prone to occlusion. There are two main locations where retinal veins are occluded. One is at the crossing of a retinal arteriole and branch retinal vein. An occlusion at a crossing of a branch retinal arteriole and branch retinal vein causes a branch retinal vein occlusion. The second is at the main trunk of the retinal vein where it leaves the eye through the optic nerve. An occlusion at the main trunk of the retinal vein causes a central retinal vein occlusion. The picture shows a photo with dilated veins and retinal hemorrhages from a fresh central retinal vein occlusion.
A branch retinal vein occlusion occurs when, because of hardening of the arteries, a branch retinal artery compresses a branch retinal vein causing blockage of the vein and decreased circulation in the distribution of that branch retinal vein. (see image) [note: the branch arteries are really arteriols and the branch veins are really veinules]
There are several possible treatments for branch retinal vein occlusion including intravitreal injections, laser, and even surgery.
Patients with BRVO lose vision for several reasons: poor circulation, hemorrhage and macular edema (swelling). There is no treatment, at the moment, to increase circulation or to remove hemorrhage. The macular edema, however, does respond well to intravitreal injections with Lucentis, Avastin, or steroids.
The inner layers of the retina receive their blood supply from the central retinal artery. The blood returns to the heart through the central retinal vein. Both vessels enter the eye through a small opening in the middle of the optic nerve. Either because this opening shrinks or because the artery hardens or because of circulations problems, the central retinal vein can become partially or completely occluded.
When a patient develops a central retinal vein occlusion (CRVO), they lose some or most of their central vision. The retinal veins dilate and their are retinal hemorrhages. Patients often develop swelling of the central retina-cystoid macular edema--causing some of the vision loss.
Without treatments, 25% of eyes improve, 50% stabilize, and 25% worsen. Monthly examinations of pateints with CRVO for less than six months are very important. Some patients with CRVO and very bad circulation, develop a severe type of glaucoma. In this situation, the eye becomes red and painful and without treatment, total visual loss can occur rapidly. If an examining doctor sees early signs that this complication may occur, then laser treatment can sometimes protect the eye. Once the pressure rise occurs, surgery can be helpful.