Retinal Vein Occlusion
What is retinal vein occlusion and what causes it?
Retinal vein occlusion is when one of the tiny retinal veins becomes blocked
by a blood clot. This means that blood cannot drain away from the retina as
easily and there is a backlog of blood in the blood vessels of the retina. This
can lead to a build-up of pressure in the blood vessels. As a result, fluid and
blood start to leak from the blood vessels, which can damage and cause
swelling of the retina, affecting your eyesight. There are two main types of
retinal vein occlusion:
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Branch retinal vein occlusion - the blockage occurs somewhere
along the course of one of the four retinal veins. (One retinal vein
drains each quarter of the eye.)
Central retinal vein occlusion - the blockage occurs in the main vein
formed by the four retinal veins coming together.
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Branch retinal vein occlusion is two to three times more common than central
retinal vein occlusion.
How common is retinal vein occlusion and who gets
it?
Retinal vein occlusion is a fairly common cause of loss of vision in the UK. It is
most common in people over the age of 60 and it seems to affect both sexes
equally.
What causes retinal vein occlusion?
The exact reason why a blood clot may form in one of the retinal veins is not
clear. However, there are some things that are thought to increase your risk of
developing retinal vein occlusion. They include the following.
Cardiovascular diseases are diseases of the heart or blood vessels caused by
atheroma. Patches of atheroma are like small fatty lumps that develop within
the inside lining of arteries (blood vessels). Atheroma is also known as
atherosclerosis or hardening of the arteries. A patch of atheroma makes an
artery narrower.
Your risk of developing retinal vein occlusion seems to be
increased if you have risk factors for cardiovascular disease. These include:
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High blood pressure - between 6 and 7 in every 10 people with retinal
vein occlusion have high blood pressure. If high blood pressure is not
well-controlled, it can also increase your risk of having another episode
of retinal vein occlusion (either in the same eye or the other eye).
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High cholesterol.
Diabetes.
Smoking.
The retinal arteries and veins run very closely together. If someone has
narrowing of their retinal artery blood vessels due to atherosclerosis, this can
make the artery blood vessels very rigid. It is thought that a rigid artery may
then press on a close-by vein and disturb the blood flow in the vein. This
turbulent blood flow means that a clot is more likely to form in the vein,
leading to retinal vein occlusion.
What are the symptoms of retinal vein occlusion?
If you have retinal vein occlusion, you will usually notice a decrease in vision
in one eye. Some people describe having a blind spot in one eye. The
condition is mostly painless unless there are complications such as secondary
glaucoma caused by new blood vessels interfering with the drainage of fluid
from inside the eye. Depending on the severity and also the degree of
involvement of the macula, retinal vein occlusions may cause only mild visual
loss in some cases or very profound visual loss in others. Some people who
only have a small blockage of a branch retinal vein may not have any
symptoms.
How is retinal vein occlusion diagnosed?
Retinal vein occlusion is usually diagnosed after an eye specialist (called an
ophthalmologist) examines the back of your eye, using an ophthalmoscope (a
hand-held instrument with a light and magnifier). They may also use a larger
special light and magnifier (which you sit at and put your chin on) called a slit
lamp. The retina at the back of your eye has a typical appearance in retinal
vein occlusion. Depending on the appearance of your retina, the specialist will
usually be able to tell if you have a central retinal vein occlusion or a branch
retinal vein occlusion. Various other tests may be suggested including measurement of your visual
acuity (how well you can see) and your visual fields (to look at how good your
side vision is). Some blood tests may also be suggested - for example, to
check your blood sugar and cholesterol levels. Your blood pressure may also
be checked. Your specialist may advise some other tests or examinations
to help to see how much damage has occurred to your retina. They are
usually done after some weeks and can help to plan which treatment may be
best for you. The tests may include:
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Special photographs of your retina.
Fluorescein angiography. A dye is injected (usually into your arm). The
dye will then pass to and move through the blood vessels at the back
of your eye and photographs can be taken with a camera to look at the
blood flow to your retina.
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Optical coherence tomography. This is a special type of test that can
measure the amount of macular oedema that you may have.
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What is the treatment for retinal vein occlusion?
Currently, there is no treatment that can reverse the blocked vein. The aims of
treatment are to detect and treat any underlying risk factors for the condition
and also to detect and treat any complications where possible.
Treating underlying problems, for example, this includes:
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Treatment of high blood pressure. (A separate leaflet called 'High
Blood Pressure (Hypertension)' gives further details.)
Treatment of raised cholesterol levels. (A separate leaflet called
'Cholesterol' gives further details.)
Good control of diabetes. (A separate leaflet called 'Diabetes Type 2'
gives further details.)
Giving up smoking if you are a smoker. (A separate leaflet called
'Smoking - Tips to Help you Stop' gives further details.)
Treatment for blood clotting disorders or rare blood problems.
Diagnosis and treatment of glaucoma.
What is the prognosis (outlook)?
Following a retinal vein occlusion you are likely to be left with some visual
loss. The extent of the visual loss can vary greatly, depending on the severity
and exact site of the vein occlusion. Early diagnosis and treatment of retinal
vein occlusion and any complications may make a difference to the eventual
level of visual loss. However, severe vein occlusions can cause permanent
visual loss, even if treated very early.
Retinal vein occlusion will recur in
about 1 in 6 people (either in the same eye or in the other eye) over the five
years following on from it.