Retinal Vein Occlusion (Blood Clot in the Eye)

What is retinal vein occlusion?

Retinal vein occlusion is a condition in which the central retinal vein, or one of its branches, becomes so narrow at some point that not enough blood can flow through it. Normally, blood enters the eye through the central artery, branches out to reach the retina and then collects in the veins until it reaches the central vein, through which it leaves the eye.

Page contents

1. What is retinal vein occlusion?
2. What types are there?
3. What are the main causes?
4. What is the treatment?
5. What is retinal artery occlusion?
6. What are the causes?
7. What is the right treatment?
8. Symptoms of retinal vein occlusion: what the patient notices
9. Ischaemic and non-ischaemic occlusion: why the distinction matters
10. Risk factors: who is most at risk
11. How it is diagnosed
12. Complications we need to prevent
13. Treatment of retinal vein occlusion in detail
14. Retinal artery occlusion: why it is an emergency
15. Prognosis: what to expect
16. Prevention and protecting the other eye
17. Daily life during treatment
18. How often follow-up is needed
19. Retinal vein occlusion or another condition? The importance of the right diagnosis
20. What to bring to your first appointment
21. Frequently Asked Questions about Retinal Vein Occlusion

At this point the artery and the vein of the eye are in very close contact, and the space at the exit point is limited. When the blood vessels of the body, and of the eye, undergo disease-related changes, mainly of the arteriosclerotic type, the space available for these two vessels is reduced and the lumen of the vessel becomes narrower.

As a result, the blood that cannot get through builds up in the network of veins just before the narrowing. In some cases the narrowing can be so severe that the vein is completely blocked. Eventually, the blood that cannot leave the eye escapes from the vessels, causing haemorrhages and oedema.

What types are there?

There are two main types of retinal vein occlusion.

Central retinal vein occlusion and branch retinal vein occlusion. Central occlusion usually has a worse prognosis than branch occlusion, while in both the loss of visual acuity can range from minimal to very significant.

What are the main causes?

The causes include all conditions that damage the blood vessels, such as high blood pressure, diabetes mellitus, high cholesterol and others. However, occlusion can also occur because of conditions that make the blood clot more easily (hypercoagulability), as well as in conditions with high intraocular pressure.

What is the treatment?

Treatment first focuses on improving all the underlying causes and then, where indicated, starting intravitreal injections and laser photocoagulation. There are two types of medication: anti-VEGF agents and steroids. There are also two types of laser and many different ways of applying it. In Oxford I gained extensive experience in this condition, in the possible treatment combinations and in the most up-to-date treatment protocols, so as to achieve the best possible result. I treated more than 1,000 patients with varying degrees of severity of the disease and all of its possible complications.

What is retinal artery occlusion?

This is a condition in which the central retinal artery, or one of its branches, cannot supply the tissues with the blood they need. This happens either because the artery itself gradually narrows or because a clot from elsewhere in the body travels with the bloodstream to the retinal arteries.

What are the causes?

The causes include all conditions that damage the blood vessels, such as high blood pressure, diabetes mellitus, high cholesterol and others. However, occlusion can also occur because of conditions that make the blood clot more easily, as well as other conditions.

What is the right treatment?

Unfortunately, a sufficiently effective treatment has not yet been found. The biggest problem is that the retina dies very quickly once its blood supply stops. The window of time available is about 3 hours. Various approaches have been tried, such as lowering the eye pressure and ocular massage, but with low success rates. After an arterial occlusion, follow-up by an ophthalmologist must continue over a long period to rule out complications caused by the occlusion.

Symptoms of retinal vein occlusion: what the patient notices

Retinal vein occlusion is usually painless. The most typical symptom is blurred or reduced vision in one eye, which many people notice in the morning, as soon as they wake up. Others notice that straight lines look wavy or that part of the image is missing, for example the upper or lower half.

How severe the symptoms are depends on where the occlusion occurred. When the central vein is blocked, the whole retina is affected and the drop in vision is usually marked. When a branch is blocked, the symptoms are limited to part of the visual field and, if the macula is not involved, it may go almost unnoticed. Many branch occlusions are found by chance during a routine eye examination.

• Blurred or reduced vision in one eye, without pain
• Distorted vision, with bent or wavy lines
• A dark area or “gap” in part of the visual field
• New floaters, when there is bleeding into the vitreous
• Pain and redness only with late complications, such as neovascular glaucoma

Ischaemic and non-ischaemic occlusion: why the distinction matters

Apart from whether the occlusion is central or branch, the ophthalmologist assesses how well the retina is supplied with blood after the event. In the non-ischaemic form, which is the more common, blood flow is reduced but the tissue still receives oxygen. The prognosis is better and vision often improves with treatment.

In the ischaemic form, large areas of the retina are left without an adequate blood supply. Tissue that is “starved” of oxygen produces substances such as VEGF, which lead to the growth of abnormal new blood vessels. These vessels are fragile, bleed and can block the flow of fluid in the front part of the eye. A non-ischaemic occlusion can turn into an ischaemic one in the first few months, which is why follow-up does not stop when vision improves.

Risk factors: who is most at risk

Retinal vein occlusion is not really an “eye problem” but a sign that the body’s blood vessels need attention. Where an artery crosses a vein, they share a common sheath. When the artery hardens, it compresses the vein, blood flow becomes turbulent and a clot forms. The main risk factors are:

• High blood pressure, the most common and most important factor
• Diabetes mellitus, which damages the walls of small blood vessels
• High cholesterol and atherosclerosis
• Glaucoma or raised intraocular pressure, which compresses the central vein where it leaves the eye
• Smoking, obesity and a sedentary lifestyle
• Age, as most patients are over 60

In younger people, under 50, without high blood pressure or diabetes, the doctor will also look for less common causes, such as blood clotting disorders (thrombophilia), autoimmune diseases, dehydration or certain medications. In these cases, working together with a physician or haematologist is essential.

How it is diagnosed

Diagnosis begins with measuring vision and intraocular pressure and continues with a dilated fundus examination. In the fundus, retinal vein occlusion has a characteristic appearance: swollen, tortuous veins and flame-shaped haemorrhages, which in central occlusion spread across the whole retina. Imaging tests are then needed:

• Optical coherence tomography (OCT): accurately measures the thickness of the macula and shows whether there is oedema. It is the key test for deciding on and monitoring treatment.
• Fluorescein angiography or OCT angiography: shows which areas are not receiving blood, in other words whether the occlusion is ischaemic.
• Fundus photography: records the appearance of the retina so that progress can be compared from visit to visit.

Because the occlusion is linked to the cardiovascular system, the ophthalmologist will recommend a blood pressure check, blood tests for sugar and lipids, and a visit to your GP or cardiologist.

Complications we need to prevent

Macular oedema

This is the most common cause of reduced vision after retinal vein occlusion. Fluid leaks from the affected vessels and builds up in the centre of the retina, where the detailed image is formed. The longer the oedema lasts, the greater the risk of permanent damage, which is why treatment starts without delay.

Neovascularisation and vitreous haemorrhage

In the ischaemic forms, the new vessels can bleed into the vitreous. The patient suddenly sees many dark spots or a “curtain”. The bleeding often clears within a few weeks, but if it persists a vitrectomy may be needed.

Neovascular glaucoma

This is the most serious complication of ischaemic central occlusion and usually appears 2 to 4 months after the event. New vessels grow on the iris and in the angle of the eye, the pressure rises sharply and the eye becomes painful and red. It is a form of glaucoma that is much easier to deal with when prevented, through regular examination of the iris and timely laser treatment.

Treatment of retinal vein occlusion in detail

There is no medicine that “unblocks” the vein after the event. Treatment targets the consequences of the occlusion, namely the oedema and the new vessels, as well as controlling the risk factors.

Intravitreal anti-VEGF injections

Today these are the first-line treatment for macular oedema. These medicines block the factor that causes fluid leakage and the growth of new vessels. The injection is given at the clinic, with local anaesthetic drops and strict sterile technique, and takes a few minutes. We usually start with monthly injections and then extend the intervals, depending on what the OCT shows. You can find out more about the procedure in our article on intravitreal injections.

Corticosteroid implant

In patients who do not respond adequately to anti-VEGF treatment or who find it difficult to attend every month, a slow-release cortisone implant that works for several months can be used. The eye pressure needs to be monitored and, in patients who have not had cataract surgery, the lens too, because the implant can speed up the development of cataract.

Laser photocoagulation

When there are new vessels or large ischaemic areas, laser is applied to the periphery of the retina. It reduces the oxygen demand of the tissue that is not receiving blood and so “switches off” the stimulus for new vessels. In selected branch occlusions it is also used for the oedema.

Retinal artery occlusion: why it is an emergency

Central retinal artery occlusion is fundamentally different from vein occlusion. It causes sudden, painless and usually very severe loss of vision in one eye, within seconds. The retina can survive only a very short time without blood, so every minute counts.

Retinal artery occlusion is considered the equivalent of a stroke in the eye. The clot often comes from the carotid arteries or the heart, and the same mechanism can cause a stroke in the following days. For this reason, the patient must go immediately to a hospital with an on-call emergency service, where a full work-up will be carried out: carotid ultrasound, cardiac assessment and, in people over 50, tests for giant cell (temporal) arteritis.

Be alert to transient loss of vision too, when one eye “goes black” for a few minutes as if a curtain has fallen, and then vision returns. This is not a harmless symptom; it is a warning. It needs assessment within 24 hours.

Prognosis: what to expect

In non-ischaemic branch occlusion the prognosis is generally good; many patients regain very good vision, either on their own or with treatment. In central occlusion the results vary. The most reliable predictor is vision at the time of diagnosis: the better it is at the start, the better it usually remains at the end. That is why starting treatment quickly matters so much.

Treatment of the oedema is often long-term. Some patients need injections for one to two years, with the intervals gradually extended. Keeping appointments is just as important as the medicine itself.

Prevention and protecting the other eye

Anyone who has had retinal vein occlusion in one eye has a small but real risk of it happening in the other. The best protection is controlling the general risk factors:

• Controlling blood pressure, with regular measurements at home
• Good control of blood sugar and cholesterol
• Stopping smoking
• Regular measurement of intraocular pressure, especially if you have glaucoma
• An annual retinal examination, or more often if your doctor recommends it

If you notice blurring or distortion of vision in one eye, book an appointment as soon as possible on +30 210 677 0007. If the loss of vision is sudden and complete, go straight to a hospital emergency department.

Daily life during treatment

Many patients worry that they will have to change their lives completely. In practice, most carry on with their work and activities as normal. On the day of the injection it is a good idea to have someone with you and not to drive, because the dilating drops blur your vision for a few hours. Mild stinging or a small red mark on the white of the eye in the first few days is common and settles on its own.

On the other hand, increasing pain, marked redness or a drop in vision in the days after the injection need immediate contact with the clinic. These are rare, but they must be dealt with straight away.

If one eye now sees less, the other takes on much of the work. Good lighting at home, larger font sizes on your phone and computer, and care on stairs help you adjust. As for driving, your ophthalmologist will tell you whether your vision meets the legal requirements.

How often follow-up is needed

The follow-up schedule is tailored to each patient. As a guide, in the first months after diagnosis visits are monthly, with an OCT scan at every visit. In central occlusion, especially the ischaemic form, we carefully check the iris and the angle for new vessels during the first six months, which is the period of highest risk. Once the oedema has stabilised, the intervals are gradually extended to two, three or more months.

At each visit we measure vision and intraocular pressure and compare the OCT with previous scans. This way we decide, based on evidence, whether to continue the injections, extend the intervals or change medication.

Retinal vein occlusion or another condition? The importance of the right diagnosis

Some conditions look similar to retinal vein occlusion on fundus examination, such as diabetic retinopathy, hypertensive retinopathy and retinal macroaneurysms. They are told apart by the pattern of the haemorrhages, whether one or both eyes are affected, and the imaging tests. The correct diagnosis determines the treatment, which is why assessment by a specialist ophthalmologist with full imaging equipment is essential.

What to bring to your first appointment

To make the assessment quicker and more thorough, bring a list of the medicines you take, recent blood test results if you have them, and the blood pressure readings you have taken at home. If you have had OCT scans or fundus photographs at another clinic in the past, they are very useful for comparison. Expect your pupils to be dilated, so do not drive after the examination and bring sunglasses with you.

Also make a note of exactly when you noticed the problem and whether your vision has changed since then. This information helps the doctor judge how recent the occlusion is and how urgent treatment is. To book an appointment, call +30 210 677 0007.

Frequently Asked Questions about Retinal Vein Occlusion

Medically reviewed by: Dr. Vasileios Skouteris MD, FEBO