Retinal Vein Occlusion

Retinal vein occlusion (RVO) is a blocked blood vessel at the back of the eye.

Retinal vein occlusion is one of the most common causes of sudden painless unilateral loss of vision. Occlusion may occur in the central retinal vein – CRVO or branch retinal vein – BRVO.

Occlusion of the retinal venous system by thrombus formation is the most common cause but other causes include disease of the vein wall and blood disorders.

Retinal arteries and their corresponding veins share a common sheath. It is thought that hardened stiff retinal artery compresses the retinal vein, eventually causing occlusion of the vein.

There are number of common conditions that increase the risk of developing a retinal vein occlusion. These include:

  • High blood pressure and high cholesterol
  • Glaucoma (High pressure in the eye that damages the optic nerve) and Ocular hypertension (High pressure in the eye without damage to the optic nerve)
  • Diabetes
  • Different blood disorders
  • Different blood vessels inflammatory diseases

Identification and treatment of any risk factors is very important to ensure that further vein occlusion does not happen, either in the same, or the other eye.

Due to the blockage of a particular retinal vein, the pressure in that veins goes up and that leads to bursting of some of the blood vessels and causing retinal bleeding.

In addition, due to the same blockage, the pressure inside the small veins and capillaries goes up and that leads to the leakage of some fluid from inside the capillaries to the retinal tissues including the macula leading to its swelling. The macula is the central, most important part of the retina that helps us seeing sharp.

All the above might leads to reduced oxygen supply to the retina – a condition called retinal ischemia. Ischaemic damage to the retina stimulates increased production of some materials called vascular endothelial growth factor (VEGF) which, in turn, may lead to further increase in capillaries permeability and more retinal and macular swelling. In addition, VEGF could stimulate the growth of abnormal unhealthy blood vessels in the retina and on the iris – a process called neovascularisation. Neovascularisation can cause haemorrhages (bleeding) as the new vessels are of poor quality or neovascular glaucoma where the new vessels grow on the surface of the aqueous drainage system that drains fluid from inside the eye out and consequently leading to severe high intra-ocular pressure that destroys the optic nerve and could lead to blindness.

Management of neovascularisation

Should you develop neovascularisation of the iris or the retina, you will be offered laser treatment called sector or pan-retinal laser photocoagulation (PRP). The presumed principle on the basis of which PRP works is thought that the neovascularisation developed due to the reduced amount of Oxygen available to the retinal tissue. Hence, by destroying the peripheral, less useful retina compared to the macula, we can reduce the consumption of Oxygen in the retina and hopefully leaving reasonable amount of Oxygen for the macula to function and that gives your eye as much vision as possible.

The risks associated with PRP or as a consequence of it are: failure to control the neovascularisation process, loss of driving licence, difficulties seeing at night and accidental damage to the macula and loss of sight.

Unfortunately, a proportion of patients with ischemic RVO will end up blind in the affected eye despite all the doctors’ efforts to save the vision.

On average, patients with BRVO require about 2 years of monitoring, and patients with CRVO required 3 years of monitoring for neovascularisation.

Management of macular Oedema

The most common reason for blurred vision in retinal vein occlusions is macular swelling – macular oedema.

Macular oedema can cause blurred or distorted vision and can lead to loss of vision. It can be difficult to treat and until recently there was no treatment available for most types of CRVO related macular oedema.

Due to recent medical research, we now have some options available, however every treatment has risks associated with it.

Options for treatment macular oedema caused by retinal vein occlusions are:

  • Do nothing, in particular in mild cases with very good vision as the swelling might settle down on its own.
  • Macular laser treatment: This was the main treatment in Branch Retinal Vein Occlusion (BRVO) until recently but it became of less use since the introduction of anti- VEGF drugs. For certain types of BRVO, occasionally and in very specific circumstances, macular laser treatment might be an option. Risks due to macular laser include: central black spot in vision due to laser scars, failure to resolve the swelling, loss of sight from accidental damage to the centre of the macula.
  • Intra-vitreal injections of Anti-vascular endothelial growth factor (anti-VEGF) and steroids intra-ocular implants.
      1. Anti-VEGF drugs are administered via an injection into the eye. They work by stopping the leakage of blood vessels on the back of the eye to prevent further damage to the macular cells and prevent loss of vision.
        The approximate percentage of patients who gain significant improvement in vision is around 50% at 12 months.
        There are two licenced anti-VEGF drugs available in the UK: Lucentis – Ranibizumab and Eylea – Aflibercept.
        The risks specific to anti-VEGF drugs include, a very small increase in risk of strokes and heart attacks due to thrombosis (about 0.4%). It is important to remember that the mean age group that gets retinal vein occlusions and the associated risk factors of high blood pressure, raised cholesterol and blood glucose, is the same group that is more prone to developing strokes and heart attacks and therefore if this unfortunate event occurs after an injection, it is very difficult to say that it wouldn’t have occurred without the injections.
        In the UK, 1 in 4000 patients develops sight- threatening infection in the eye due to intra-vitreal injections of anti-VEGF.
      1. Ozurdex – Biodegradable Dexamethasone Implant: It is also an intra-vitreal injection as anti-VEGF however, the needle is thicker. The steroid implant provides slow release of the active drug – Dexamethasone that lasts for up to 4 to 6 months. The treatment is administered every 4-6 months on average for as long as the macular swelling keeps developing. You will also be required to see the eye doctor for monitoring in between injections.
        Its main side effect is raised intraocular pressure in about 30% of patients that might require treatment with hypotensive eye drops to control the eye pressure or rarely glaucoma surgery. Uncontrolled eye pressure can lead to glaucoma and deterioration of vision over time. Your eye pressure will be monitored for this reason. A patient who has established glaucoma may not be suitable for this treatment as it may make the control of the intraocular pressure difficult.
        Ozurdex can cause or speed-up the development of cataracts.
      • The injection
        Before the injection, both you and your eye doctor will need to sign a consent form. The procedure takes a few minutes but the injection itself is done in a few seconds. It is given in a clean room while lying on a couch. The eyelids and surface of the eye are cleaned first to reduce the risk of infection.The eye is first made numb with eye drops. During the injection, you will feel a prickle or a pressure type sensation similar to taking blood from your arm.
      • Risks that are common to all injections treatment options
        1. Conjunctival bleeding on the surface of the eye – often painless, and resolves with no treatment within 1-2 weeks.
        2. Corneal abrasion that gives you pain shortly after the injection for about 24-48 hours until it heals completely.
        3. Infection inside the eye that might cause loss of vision (endophthalmitis) – very rare.
        4. Bleeding into the gel of the eye.
        5. Lens touch causing cataract (clouding of the lens within the eye).
        6. Raised intraocular pressure leading to glaucoma (more common in the Ozurdex group).
        7. Retinal detachment.
        8. Hypotony (reduced pressure in the eye).
      • How often will you require treatment with anti-VEGF?
        Initially, you should prepare yourself to see your eye doctor every 4-6 weeks. Later, the management and the intervals between visits will be tailored individually to yourself for as long as the macular swelling keeps recurring. The first three visits will require you to have an injection on a monthly basis, then you will be offered an injection if there is evidence that the leakage is still active. In one year, the average patient may have up to 8-9 injections and in the second year, approximately 6-7 injections. This is only indicative as each eye is unique.
      • How often will you require treatment with Ozurdex?
      • On average 2 implants per year are required and an average of 7 visits per year to the clinic are required to include the essential monitoring of your eye in between the treatments.