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Retinal Vein Occlusion

Retinal Vein OcclusionThe treatments for this condition have changed considerably over the past few years so a detailed explanation of what the problem is and how it is best managed is given here. Please be aware that the treatments mentioned here refer to those available on the NHS in the UK.

About the normal retina

The retina is the light sensitive film at the back of the eye. It has light sensitive cells (rods and cones) and these convert the light that is focused onto the retina by the lens system of the eye into electrical (nerve) energy. These nerve impulses are sent by the optic nerve to the brain and are converted into vision. The centre of the retina has a much higher concentration of these light sensitive cells and as such the central retina (which is called the macula) is the most sensitive part. We use this central retina (macula) for detailed vision such as reading and recognising faces.

The retina is a very active tissue and therefore needs a large blood supply to keep it going.  Blood is brought into the retina by a large artery which divides into smaller arteries that spread all over the retina. These flow into the much smaller vessels called capillaries. The capillaries form a fine network of tiny blood vessels throughout the retina. All the exchange of nutrients, oxygen and waste products occurs between the cells of the retina and the blood in the capillary network. From the capillaries the blood drains into at first small veins that eventually join the large vein of the eye (at the same place that the artery enters the eye) and the “used up” blood is drained away from the eye through this large vein. So, fresh oxygenated blood comes into the eye, it supplies the retina with oxygen and nutrients in the capillary network, then drains away in the veins.

What is a retinal vein occlusion?
The flow of blood through the retina is continual, if the outflow is obstructed for any reason, especially in the large veins, then blood can get in but can’t get out. Like on a motorway with all three lanes blocked, the flow of blood (traffic on a motorway) soon comes to a halt. As a result the area of retina affected by the block suffers damage. The damage is for two reasons, firstly the retinal cells are starved of nutrients and secondly there is pressure damage to the delicate capillaries. If the main vein is blocked (a central retinal vein occlusion) then most of the retina is damaged and the vision in that eye deteriorates markedly. If one of the smaller veins is blocked (a branch retinal vein occlusion) then there is less retinal damage. However if a relatively small area of retinal damage includes the very sensitive central retina (macula) then this has a disproportionate effect on the vision loss experienced.

Retinal Vein Occlusion

Branch retinal vein occlusion. Note the bleeding from the burst capillaries. The centre of the retina (macula) is involved so the vision will be poor

When the macula is included in the damage it always responds by becoming swollen. This is referred to as macular oedema. Where there is not too much retinal damage (branch retinal vein occlusion) this swelling of the macula may well settle down on its own and the vision improve. If there is a lot of retinal damage then the swelling may not settle and treatment may be required.

Retinal Vein Occlusion

Layers of a normal macula, the dimple (F) is normal Macular oedema, note the swollen fluid filled area in the centre

The cause of retinal vein occlusion is thought to be furring (thickening) of the nearby arteries of the retina which press on the vein and block it off. Furring of the arteries is more common in smokers, people with high blood pressure and diabetics. Sometimes no particular cause is found and the furring of the arteries is down to ageing.

Symptoms of retinal vein occlusion

Both central retinal vein occlusion and branch retinal vein occlusions present with a sudden loss of vision in the affected eye.  If there is a branch retinal vein occlusion and the macula (central retina) is not damaged, then there may be no obvious effect on the vision and the problem is picked up incidentally by that person’s optician.

Treatment of retinal vein occlusion

The most important thing is to see if there is an underlying cause. Your doctor will check your blood pressure and also perform a diabetes test. You will also be asked about smoking. Dealing with these important risk factors significantly reduces the chances of the same thing happening to the other eye. You will also be referred

Retinal Vein Occlusionto an eye surgeon who will confirm whether you have a central or branch retinal vein occlusion. The management differs depending on which type of vein occlusion you have.

In a branch retinal vein occlusion the patient is monitored to see if the vision recovers without any treatment. If there is little or no improvement, usually due to the macula being swollen, then treatment will be considered. Treatment is aimed at reducing this swelling (macular oedema). The traditional treatment for macular oedema is to apply gentle laser burns to the macular area. Several laser treatments may be required. Either prior to the treatment, or if laser does not work, another test will be performed where dye is injected into the arm and this outlines the retinal blood vessels. This is called a fluorescein angiogram.

A fluorescein angiogram (black and white picture with the blood vessels full of dye) shows the damaged, dilated vessels

The reason for this is to assess if there is a lot of damage to the capillaries around the macula. If there is a lot of damage (this is called ischaemia) then laser treatment is less likely to work. The aim of any treatment is to resolve the macular oedema. If the oedema does not resolve then the vision will remain poor.

There are now other treatments that may improve macular oedema (and therefore the vision) in cases where laser has failed or felt to be inappropriate. Injecting steroid drugs into the eye may result in an improvement of the macular oedema but this is usually only temporary. There is a longer lasting steroid injection (Ozurdex, a steroid implant - see below) that reduces the need for regular injections. However the drug can cause cataracts and glaucoma. If the risk of either of these two problems is high then another drug (lucentis) may be used instead.
Injecting any drug into the eye carries a small risk of serious infection of the eye. Also if there is a lot of damage to the blood vessels of the macula, these new treatments may not work.

In central retinal vein occlusion the chance of improving the vision is less than with a branch retinal vein occlusion because the amount of damage is so much greater. The amount of macular oedema (swelling) is usually large and does not respond to laser treatment at all. The traditional management is to look for underlying causes and then monitor the patient. One of the problems with this condition is that abnormal blood vessels can develop within the eye and cause other problems. One of these is that the pressure in the eye begins to rise (glaucoma) to the point where the eye not only cannot see but is painful as well. This problem usually happens about three months after the onset of the occlusion. There are some tell tale signs that the eye doctor will look for to see if the pressure problem is likely to develop. If so laser treatment (to the whole retina not just the macula) is given to prevent the problem developing. This laser treatment will in no way improve the vision; the sole aim is to keep the eye comfortable.

Retinal Vein Occlusion

Central retinal vein occlusion. There is extensive damage of the retina as indicated by widespread bleeding within the retina. The vision is likely to be severely affected

There are also other treatments for central retinal vein occlusions that can help improve the vision. Steroid injections (Ozurdex) into the eye do help more in this condition.  Once again the side effects of steroids in the eye (cataracts and glaucoma) can occur with this implant though the incidence of these side effects is not as high as with other types of steroid injections. If steroids are thought to be worth trying, you may be asked to use steroid drops for a few weeks to see if you are at risk of developing glaucoma with steroid injections.

Retinal Vein Occlusion

Ozurdex implant being injected into the eye Lucentis/Avastin being injected in to the eye

In the same way as for branch retinal vein occlusions, injecting drugs (Lucentis) into the eye that stop blood vessels leaking can help improve the macular oedema and therefore the vision. The advantage of these drugs over Ozurdex implant is that they do not have the side effects of glaucoma and cataract. If the risks of this are thought to be high then lucentis will be tried instead of Ozurdex. The disadvantage of lucentis is that it has to be injected more frequently (once a month as against once every few months).

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