Obstruction of a retinal vein causes elevation of capillary pressure and a slowing of blood flow in the area drained by the vein. With moderate venous obstruction, the leakage of red blood cells and serum into the retina will cause permanent damage to the retinal receptor cells.
Central retina vein obstruction
The venous impingement occurs, in such cases, within the nervehead. See below
The obstruction can involve one or more branches within the retina or, less commonly, the central vein for the entire retina. Branch obstructions generally have a better prognosis for visual return than central vein obstruction.
Patients experiencing retinal vein obstruction consistently manifest retinal arteriosclerosis that has developed as a result of longstanding hypertension of mild to moderate degree. More important than the degree of blood pressure elevation, in the creation of arterial wall hardening, is the length of time (the chronicity) during which the hypertension has been present.
Branch vein obstruction
Only a portion of the retinal venous system is involved. See below
For central vein obstruction a medication (vascular endothelial growth factor – Avastin, usually) is injected through the wall of the eye and into the vitreous. The medication diffuses posteriorly to the site of the obstruction and oftentimes speeds the blood flow within the retinal veins. Sometimes, an operative procedure (vitrectomy) is also necessary. During the latter procedure the optic nerve sheath is incised to relieve compression on the central vein.
For retinal venous obstruction a low sodium diet and oral aspirin can also aid the retinal blood flow. Both aspirin and the low sodium diet assist the flow of blood past the obstruction site.
Laser coagulation of leakage sites is adjunctive treatment for both central and branch vein obstruction.