Retina, the main part of visual sensation has got numerous retinal vesselsto give a good blood supply. "Retinal arteries" bring the blood from heart to the retina while "Retinal veins" drain the blood from the retina towards the heart. There is one main Central Retinal Artery (CRA) and one main Central Retinal Vein (CRV). They give origin to numerous branches.
There may be an obstruction to the blood flow in retinal veins,either in the branches or the central retinal vein. This is one of the common causes of vascular problems in retina. Because of this obstruction, blood drainage from retina to heart is hampered. "Branch Retinal Vein Occlusion" or BRVO denotes obstruction of this blood flow in small branches of retinal veins while "Central Retinal Vein Occlusion" or CRVO denotes obstruction of blood flow in the main and largevein of the retina.
Common Causes :
- Idiopathic, meaning no known cause
- Increased blood pressure, which is either not properlycontrolled or is fluctuating.
- High serum lipids or cholesterol and diabetes mellitus
- High intra ocular pressure what we call as glaucoma
- There are many other uncommon causes
Mechanics of Obstruction:
In the retina, arteries and veins cross at many locations. In case of high blood pressure, arteries become rigid and hard and they cause pressure over the soft veins at the point of crossing, so blood flow from these veins is obstructed.