What are retinal veins?
These blood vessels drain blood from the retina and take it back through the optic nerve at the back of the eye.

How do retinal veins become blocked?
Most retinal veins traverse the retina closely followed by (and sometimes intertwined with) retinal arteries. As we age, the walls of arteries (including in the retina) can harden – especially in patients with high blood pressure. If a retinal artery wall hardens enough, and if an eye has a point where a branch retinal artery crosses above a branch retinal vein, the hardened artery can push on the vein, causing the vein to narrow, increasing the likelihood of occlusion. Thrombosis (clot formation) is also involved, especially in central retinal vein occlusion (see below).

What are the risk factors for RVO?
The biggest risk factors are increasing age, and high blood pressure.

What are the types of retinal vein occlusion (RVO)?
The two main types are branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO):

What are the consequences and complications of RVO?
This depends on whether a branch vein or the central vein has occluded (BRVO and CRVO respectively) as well as whether the blockage was partial or complete. The spectrum is wide – mild RVO can sometimes cause no symptoms, while severe RVO can cause almost complete loss of vision. The specific adverse effects include:

• swelling or loss of blood supply to the macula, causing reduction in central vision
• growth of new vessels on the retina, causing potential vitreous haemorrhage
• growth of new vessels on the iris, causing potential rubeotic glaucoma
• growth of scar tissue on the macula (secondary epiretinal membrane)

What investigations are needed in RVO?
These could be divided into systemic tests and eye tests:

• systemic tests
  • blood pressure + routine blood tests including ESR / plasma viscosity are generally advised
  • serum protein electrophoresis (if ESR or plasma viscosity is elevated) – this is principally to look for myeloma / monoclonal gammopathy, of which the first manifestation is (rarely) a retinal vein occlusion
• eye tests
  • intraocular pressure (IOP) – occasionally, RVO is a presenting feature of ocular hypertension or glaucoma
  • colour photography – to document haemorrhages, exudate deposition, new vessels etc
  • fluorescein angiography – to define areas of ischaemia (lost blood supply), leakage (macular oedema), and possible new vessel formation
  • optical coherence tomography (OCT) – to quantify macular swelling and monitor its response to treatment

How is RVO treated?
This depends on the type and location of RVO, but options include:

• observation only – mild RVO can often improve spontaneously within a few months
• retinal laser treatment – either panretinal laser, sector panretinal laser or macular grid laser
• intravitreal injections – for macular swelling or for rubeosis (abnormal new blood vessels)
• intravitreal steroid implants – for macular swelling
• vitrectomy – if there is vitreous haemorrhage or secondary epiretinal membrane