Retinal Vein Occlusion

What is a retinal vein occlusion?



All tissues in the body need a blood supply to function as the blood provides the cells with oxygen and sugar which they need to survive. The blood going to the tissues from the heart travels in blood vessels called arteries. These then divide up into much smaller blood vessels called capillaries where the oxygen and sugar is given to the cells and the waste products such as carbon dioxide are given back to the blood. These capillaries then join up to form larger blood vessels once more called veins which return the blood to the heart.

The retina (photographic film at the back of the eye) has a single large vein called the central retinal vein and if this is blocked results in a condition called a central retinal vein occlusion (CRVO) which affects the whole circulation of the retina with general blurring of vision in one eye. Sometimes one of the smaller veins blocks instead and this is called a branch retinal vein occlusion (BRVO). This will affect a patch of the retina and cause a patch of blurred vision in one eye. Most patients with retinal vein occlusions have blood pressure as an underlying cause and so blood pressure control is very important.

It is rare that both eyes are affected at the same time with this condition.

The poor circulation in the retina results in 2 problems, blockage of blood vessels and leakage from blood vessels. If leakage occurs in the central part of the retina (macula) it results in the retina becoming thickened and waterlogged and therefore not able to function well and you become aware of blurring of vision.

If blockage is the main problem then the body tries to improve the circulation by producing new blood vessels. Some of these blood vessels are helpful by bypassing the blockage and they are called collateral blood vessels. Unfortunately some of the blood vessels are not helpful as they either grow from the retina into the clear jelly (vitreous) that occupies the main eye cavity (usually seen with BRVO) or grow at the front of the eye on the iris (coloured part of the eye) and this is usually seen in patients with severe CRVO.

The blood vessels that grow into the jelly can rupture resulting in haemorrhage into the jelly and patients often notice sudden large floaters and blurring of vision. When blood vessels grow on the iris it impairs a circulation of clear fluid called aqueous. The eye has its own pressure (above atmospheric pressure) that is required in order for it to function and this eye pressure is a result of a balance between the production of aqueous by the eye and drainage of aqueous from the eye.

This eye pressure is not the same as blood pressure. The abnormal blood vessel on the iris seen in some patients with severe CRVO are associated with scarring which obstructs the drainage of aqueous from the eye and results in the pressure in the eye increasing. Glaucoma is a condition where the pressure in the eye is too high and these blood vessels on the iris produce a rare but serious type of glaucoma called thrombotic or rubeotic glaucoma. The pressure can become very high with this type of glaucoma resulting in pain and worsening of vision.

What is the treatment of retinal vein occlusion?



Retinal vein occlusions can be associated with high blood pressure so it is important that your blood pressure is checked and it is also worth having a blood test to make sure your blood sugar and cholesterol are not too high. Many vein occlusions result in leakage from the small blood vessels called capillaries causing leakage with water logging and thickening of the retina. This often occurs in the centre of the retina and this is called macular oedema and results in blurring of vision. There are several treatments available for this condition. If the macular oedema is due to a branch retinal vein occlusion (where just a part of the retina is affected by the blockage) then sometimes things can improve spontaneously. Laser treatment has been available for many years for leakage from branch retinal vein occlusion.

It involves placing some drops to numb the surface of the eye and enlarge the pupil then a contact lens is gently placed on the eye to focus the laser beam. You are often aware of a red light during the procedure which is the laser aiming beam. The treatment usually lasts a few minutes only and no special precautions need be taken after the treatment. The laser energy used for this technique is kept to a minimum and it is not a painful treatment. Several laser burns are applied in the area of leakage (where the retina is thickened and waterlogged) avoiding the very centre of the macula.

The exact reason why this technique reduces the leakage is still not fully understood but if an improvement occurs it takes a few weeks to months to fully have its effect. Laser treatment is still however “destructive” as each laser burn destroys a small area of the retina in the hope of improving the overall situation in the rest of the centre of the retina. Laser cannot be given if there is a large amount of bruising (haemorrhage) at the macula or if the leakage is from a central retinal vein occlusion. Other treatments have therefore been developed including the use of steroid injections and the drugs Eylea, Lucentis and Avastin.

Steroids are effective at reducing inflammation and inflammation is seen in retinal vein occlusions. Most people needing steroids to reduce inflammation elsewhere in the body need to take them in tablet form and unfortunately there are a large number of side effects when taking them as tablets. Inflammation in the eye however can be treated by a local injection of steroid in or around the eye without all the side effects associated with taking tablets.

Ozurdex (Dexamethasone) is a slow release steroid capsule that is injected into the main eye cavity (vitreous cavity) an slowly dissolves over a period of about 4 months and therefore ensures treatment of inflammation over this period.

The injection is given as a day case procedure in theatre. Drops are given to numb the surface of the eye and then a solution of weak iodine is placed on the surface of the eye and the skin around the eye also cleaned with iodine (unless you are allergic to iodine when another cleaning solution is used). This may sound old fashioned but iodine is still the best thing for quickly destroying any bugs (bacteria) that are on or around the eye and therefore minimises the risk of infection. The face is then covered with a light paper drape with a small hole that allows access to the eye that is having the injection. The drape is held away from the face so that you do not feel claustrophobic. A small instrument called a speculum is placed to keep the lids apart and stop you from blinking so sometimes you are aware of a gentle pressure on the lids that can feel a little strange but is not painful.

You may be asked to look in a particular direction when the local anaesthetic is given. The eye will then be completely numb and you will not feel the injection of steroid into the eye. Sometimes you notice a floater soon after the injection but this usually settles as the capsule sinks to the lower part of the eye cavity and out of sight. No stitches are needed. After the injection the drape is removed (and sometime there is a little pulling on the skin as it is removed) and an antibiotic drop given.  

Sometimes you may be asked to put antibiotic drops into the injected eye four times a day for 5 days to also minimise the risk of infection. This is performed by first washing your hands then gently pulling the lower lid down and away from the eye and placing a drop in the groove created between the inner aspect of the lower lid and the eye. If you think you have “missed” put another drop in as you cannot “overdose” on these eye drops. There are no other “dos or don’t” after the injection.

The ozurdex injection usually starts to dry up the retina within a week or two and as it does most patients will also notice an improvement in vision. This effect usually lasts for about  3 to 4 months. The hope is that by this time the circulation is starting to improve on its own but if not the injection can be repeated. There is a 1 in 1,000 risk of infection with any injection into the eye and this includes the ozurdex injection. There is also a risk that the pressure in the eye can increase following steroid injections but usually this is a temporary feature and can be treated by drops alone.  Ozurdex however is used with caution if you already have severe glaucoma.  Multiple Ozurdex injections (usually more than 3) will result in cataract formation but this can be sucessfully treated with surgery.

Laser treatment has only been found to be effective in treating leakage and water logging of the macula for branch retinal vein occlusions and not central retinal vein occlusion (when the entire retina is affected). The Ozurdex injection however can be of benefit in treating leakage from central retinal vein occlusions as well.

The anti-VEGF agents Eylea, Lucentis and Avastin which have been used extensively in wet age-related macular degeneration have also been shown to be effective in treating leakage in both branch and central retinal vein occlusion. The duration of action however is shorter lived than the Ozurdex injection and does need repeated injections with at least 1 month between injections. The total number of injections needed is variable and depends on the severity and duration of the leakage. The advantage of Eylea, Lucentis and Avastin injections is that they can be safely given if the patient is being treated for glaucoma (high eye pressure) as the Ozurdex can make glaucoma worse and these injections can be given in a dedicated room as an out-patient procedure with local anaesthetic drops alone.

Patients with severe central retinal vein occlusions can develop a rare but serious complication of their condition called rubeotic or thrombotic glaucoma. In this situation there is very poor circulation to the retina and it results in new blood vessels developing but not in the retina where you would expect them to develop but instead they develop on the surface of the iris (the tissue at the front of the eye which gives the eye its colour).

These abnormal blood vessels are associated with some scar tissue and they block the circulation of a clear fluid called aqueous at the front of the eye which is responsible for keeping the pressure in the eye at a certain level. The aqueous cannot flow out of the eye so well but it still keeps being produced and this results in the pressure in the eye suddenly becoming very high and the eye becomes red and painful and the vision gets even worse. This unpleasant condition usually develops several months after the initial loss of vision associated with the central retinal vein occlusion. Patients at risk of this condition should have a test called an FFA (Fundus Fluorescein Angiography) performed. This involves an injection of iodine dye into a vein in the arm and then taking photographs of the retina as the dye circulates. The gives a very accurate assessment of the circulation at the back of the eye and in particular if there is poor circulation and therefore an increased risk of rubeotic glaucoma. You sometime feel a little nausea for a few minutes after the injection and your skin (and subsequently your urine) turns yellow for a few hours afterwards.

If you are at high risk of rubeotic glaucoma then urgent and extensive laser treatment to the retina is needed to prevent this complication developing. This laser treatment is called pan retinal photocoagulation (PRP). It is often easier to give a local anaesthetic injection prior to this sort of laser as the extensive treatment can sometimes be uncomfortable if an injection is not given. It must be emphasised however that this laser is very different to the small amount of laser needed to treat leakage in patients with branch retinal vein occlusion discussed earlier. Laser to prevent rubeotic glaucoma does not usually improve the vision. It is to prevent the vision getting worse and the eye becoming painful. If you have already developed rubeotic glaucoma then laser can sometimes still be effective and also the anti-VEGF agents Eylea, Lucentis and Avastin can be of benefit in treatment.