Explaining the Types of Retinal Vein Occlusions and How they Occur

There are two types of retinal vein occlusions. They are differentiated on the basis of whether the entire retinal vein is blocked (CRVO) or whether a branch of the central vein is blocked (BRVO).

Central Retinal Vein Occlusion (CRVO)

CRVO is a blockage of the main vein leading out of the eye. This vein drains the major artery that feeds the inner layer of the retina.

• Blockage of the vein results in engorged, tortuous veins and superficial, flame-shaped retinal hemorrhages.
• Vision loss from CRVO is highly variable.
• In severe (ischemic) CRVO, vision loss is profound and seldom improves.
• In the milder form (non-ischemic), vision loss may be mild.

Branch Retinal Vein Occlusion (BRVO)

BRVO is a blockage of a branch of the central retinal vein. Again, only a portion of the retina and the corresponding visual field is affected.

• BRVO are usually of the milder (non-ischemic) form, though there are exceptions.
• Because the BRVO affects only the upper or lower half of the retina, it may not reduce central vision. Patients are sometimes unaware they have lost vision at all.

Watch for These Related Health Risks...

Retinal vascular occlusions of the ischemic (severe) variety, usually CRVO, can cause serious problems besides the vision loss.

Neovascular glaucoma occurs in nearly half the ischemic cases and can cause the loss of the eye if not promptly diagnosed and controlled.

Treatment of neovascular glaucoma involves pan-retinal photocoagulation (see PRP under Diabetes) and sometimes injections of anti-VEGF drugs like Avastin or Lucentis.

Because of this, and because nearly 20% of non-ischemic (milder) cases can convert to ischemic form, it is critical for CRVO and BRVO to be followed closely for up to a year.

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