Retinal vein occlusion is when one of the tiny retinal veins becomes blocked by a blood clot. It usually leads to a painless decrease in vision in one eye. Risk factors include high blood pressure, high cholesterol levels, diabetes, smoking and glaucoma (raised pressure in the eye). Treatment includes treating any possible risk factors and also treating any complications.
Some anatomy of the eye
When you look at an object, light from the object passes through the cornea of your eye, then the lens, and then it hits the retina at the back of your eye. The cornea and the lens both help to focus the light on to your retina.
Nerve messages pass from the seeing cells (rods and cones) in your retina, down nerve fibres in your optic nerve to your brain. The messages are interpreted by your brain, which enables you to see. If the retina is damaged, a clear picture cannot be produced.
The inner layers of the retina get their blood supply from the retinal arteries and retinal veins which run within the retina itself. The retinal arteries help to take oxygen and nutrients to the retina. The retinal veins drain blood away from the retina and back towards the heart.
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:
• 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.
Branch retinal vein occlusion is two to three times more common than central retinal vein occlusion.
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.
• High blood pressure – 60 – 70% of 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.
• High cholesterol.
• Blood clotting disorders
What complications does retinal vein occlusion cause?
There are some complications that can develop if you have retinal vein occlusion, which may lead to worsening visual loss. The complications can include:
• Macular oedema. This is swelling of the macula, which is the specialised central area of the retina that we use for detailed vision. Macula oedema is usually the main reason why someone with retinal vein occlusion may develop visual problems.
• Neovascularisation. This is abnormal new blood vessel formation in the eye. If abnormal new blood vessels form, this can sometimes lead to increased pressure within the eye and to glaucoma. Also, the new blood vessels are of a poor quality and can sometimes bleed, reducing the vision further.
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 treated?
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.
Macular oedema from vein occlusion is most often managed by injections of medication into the eye to reduce the swelling. The most commonly used medication for this at Retina Specialists is Avastin, but other possibilities include Lucentis, Eylea and steroid preparations such as triamcinolone.
Neovascularisation is managed with a combination of laser treatment and injections of Avastin.
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.
The doctors at Retina Specialists are Southern Cross-affiliated providers for OCT scans and intravitreal injections, commonly required in the management of retinal vein occlusions.