Central retinal vein occlusion - the blockage occurs in the main vein formed by the four retinal veins coming together.īranch retinal vein occlusion is about three times more common than central retinal vein occlusion.(One retinal vein drains each quarter of the eye.) Branch retinal vein occlusion - the blockage occurs somewhere along the course of one of the four retinal veins.There are two main types of retinal vein occlusion: If only one of the four branch veins is blocked, the other three will still drain blood away from the macula. This is more likely to occur in central retinal vein occlusion, as drainage of blood from the macula is usually shared by all four retinal branch veins. If this bruising and swelling occur at the centre of the retina (the macula) then central vision can be affected. The blood 'backs up' behind the blockage, and fluid and blood leak from the blood vessels into the delicate tissue of the retina, forcing its layers apart and affecting its ability to respond to light. This means that blood cannot drain away from the retina as easily. Retinal vein occlusion occurs when one of the four retinal veins, or the central vein, becomes blocked by a blood clot. Its rich blood supply is drained away by four retinal veins, which feed into one central retinal vein which drains out of the eye. It is delicate, is made of several layers, and needs a good supply of oxygen. The retina is a thin, light-sensitive membrane that lines the back of your eye. This gives a very detailed 'cross-sectional' image of the layers of the retina, showing where there is swelling and damage, and how severe it is. It is particularly helpful for identifying new vessel formation. Then photographs can be taken with a camera to look at the blood flow to your retina. This dye will then pass to, and move through, the blood vessels at the back of your eye. A dye is injected (usually into your arm). This allows the ophthalmologist to look in detail at the blood vessels in the eye, and how the blood is flowing through them. These show the overall image of the retina, allowing the ophthalmologist to see which areas appear to have sustained damage. The tests are usually done after some weeks have passed. These images can help see exactly how much damage has occurred to the retina and whether (and how) it might be improved. Your blood pressure may also be checked.Ī number of techniques can provide accurate digital images of the retina and its blood circulation. Some blood tests may also be suggested - for example, to check your blood sugar and cholesterol levels. Various other tests may be suggested, including measurement of how well you see (your visual acuity) and your visual fields (to look at how good your edge (peripheral) vision is). From the appearance of your retina, the specialist will usually know if you have a central retinal vein occlusion or a branch retinal vein occlusion. The retina at the back of your eye has a typical appearance in retinal vein occlusion. They may also use a larger special light and magnifier (which you sit at and put your chin on) called a slit lamp. Retinal vein occlusion is usually diagnosed after an eye specialist (an ophthalmologist) examines the back of your eye, using an ophthalmoscope. This is more commonly seen in central retinal vein occlusion, which affects the whole of the retina, (including the macula where central vision is formed). Retinal vein occlusion can cause very profound visual loss. Some people who only have a small blockage of a branch retinal vein may not have any symptoms. The condition is mostly painless unless there are complications, such as secondary raised pressure in the eye (glaucoma) caused by new blood vessels interfering with the drainage of fluid from inside the eye.ĭepending on the severity and also the degree of involvement of the macula, retinal vein occlusions may cause only relatively mild visual loss. Some people describe having a blind spot in one eye. If you have retinal vein occlusion, you will usually notice a decrease in your vision in one eye. What are the symptoms of retinal vein occlusion? This blockage may occur either because of pressure on the outside of the vein (usually from a retinal artery) which squashes or kinks it, or because of sludging of fatty deposits or clotting of blood inside the vein, forming a plug.Ĭonditions which increase the risk of retinal vein occlusion include: It is most common in people over the age of 60 years. Retinal vein occlusion is a fairly common cause of loss of vision in the UK.
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