What Is Retinal Vascular Occlusion?
Retinal vascular occlusion, also known as retinal vein occlusion, is a blockage in the veins of the retina. There are two main types: branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO). A blockage in both is thought to be caused by pressure on the vein from outside. These are NOT ‘like a stroke in the eye’ and are not generally caused by problems with blood clotting. The most common cause of these is high blood pressure. Follow this link for more information about retinal blood vessels.
Central Retinal Vein Occlusions.mp4
Dr Chauhan explains central retinal vein occlusions
Can Retinal Vein Occlusion Be Cured?
While there is currently no cure for reduced eyesight caused by retinal vein occlusion, treatment is available that can either keep vision stable or improve it. There are several types of treatment used in retinal vein occlusions. These include:
- Intravitreal injection
- Laser photocoagulation
- Vitrectomy surgery
The choice and timing of treatment is dependent on many factors as well as the results of tests.
What Is Branch Retinal Vein Occlusion?
When a retinal artery lies on top of a retinal vein, any ‘hardening’ of the artery from high blood pressure can compress the vein. This can suddenly stop the blood flowing through the vein, leading to a pressure build-up in the smaller veins and capillaries that drain through it. The damaged capillaries bleed into the retina at the time of the occlusion (blockage) and can start to leak, which may continue permanently. If the capillaries have been so badly damaged that no blood flows through them, this is known as an ischaemic retinal vein occlusion; if not, then it is known as non-ischaemic. Both can have a variable immediate effect on vision that can change with time, but ischaemic vein occlusions can lead to later problems. Only a part of the field of vision is usually affected, but this may well include the macula and cause central visual loss.
Colour photo of a macular branch retinal vein occlusion with haemorrhages affecting the macula
Fluorescein angiogram of the a patient showing leakage of dye (white) from a damaged vein due to a branch retinal vein occlusion
An OCT scan through the centre of the macula showing the macular oedema, or fluid (dark zone), within the macula
How Does High Blood Pressure Affect Your Eyes?
Untreated high blood pressure can cause damage to tiny retinal vessels, leading to retinal vein occlusion and a reduction in eyesight.
As a result of this, blood is unable to drain away from the retina, causing a build up of pressure.
This pressure then leads to fluid and blood leaking from the vessels, causing swelling of the retina that affects eyesight.
What Is Central Retinal Vein Occlusion?
In central retinal vein occlusion, the site of blockage cannot be seen, as it does not occur in the retina but within the optic nerve instead. Bleeding and leakage of retinal capillaries is similar to that in BRVO but involves the whole retina, causing the entire field of vision to be affected. CRVOs can also be non-ischaemic, but it is ischaemic CRVOs that are a potentially serious threat to the eye and its vision. Without treatment, ischemic CRVOs can lead to very painful eyes.
CRVO with relatively little haemorrhage but a lot of macular oedema and some engorged veins
What Causes Retinal Vein Occlusion?
Branch retinal vein occlusions usually occur in people over 50 years old and are more common in people with high blood pressure (hypertension). If there is not already a history of hypertension, it is definitely worth being tested thoroughly for this, which may well include a 24 hour blood pressure monitor. In many patients, no obvious cause is found.
Central retinal vein occlusions also occur in the same age group and are associated with high blood pressure, smoking, and glaucoma.
How Is Vision Affected?
Patients with both branch and central retinal vein occlusions usually describe a sudden painless blurring of vision in one eye that may affect near and distance vision. Sometimes, this is not noticed until the unaffected eye is covered by chance. This blurring does not usually change very much over the first few weeks. However, it is very important to be checked urgently, as these symptoms are very similar to those of other conditions that may need immediate or urgent treatment.
How Does Retinal Vein Occlusion Reduce Vision?
There are three ways in which retinal vein occlusions cause reduced vision:
When a vein occlusion occurs and there is an increase in the pressure within the vein, there can be either temporary (weeks to months) or permanent damage to the capillaries that makes them leaky. As a result, the macula becomes waterlogged and swollen. This is called macular oedema and can be shown both on OCT scanning and fluorescein angiography (FA). OCT scanning is better for monitoring the amount of macular oedema, as measurements can be made of the thickness of the macula as well as its volume and changes in both over time. FA is better at demonstrating which capillaries are leaking and may need treatment.
When a retinal vein occlusion occurs, the sudden rise in pressure in the capillaries can cause blood to escape from the capillaries – bleeding. The blood, which is in patches within the retina, blocks light getting to the photoreceptors (light-sensing cells), resulting in vision being blocked in patches. If this involves the fovea, it can cause severe visual loss.
This bleeding may well be a one-off event and the blood may clear over weeks to months. In many, however, persistent damage to the capillaries means that blood may continue to leech out and the vision can be affected for much longer.
If the damage to the retinal capillaries at the time of the vein occlusion is severe, they may become permanently damaged and blocked. This is called ischaemia, and if it occurs, the area of retina in which this occurs will never work normally again. When the fovea or macula becomes ischaemic, central vision can be permanently lost.