Overview
A retinal artery occlusion occurs when the central retinal artery or one of the arteries that branch off of it becomes blocked. This blockage is typically caused by a tiny embolus (clot) in the blood stream. The occlusion decreases the oxygen supply to the area of the retina nourished by the affected artery, causing permanent vision loss.
About the Retinal Vessels
The retina at the back of the eye requires a constant blood supply. This blood supply makes sure that the cells of the retina get all the nutrients they need to continue working. The blood supply also removes any waste material that the cells have finished with. Like the rest of the body there are two types of blood vessels concerned with the blood supply to the retina, arteries and veins, Arteries carry the fresh blood from the heart and lungs to all the cells in our bodies. Veins take away the blood that has been used by the cells and return it to the lungs and heart to be refreshed with oxygen and other nutrients. This process happens every time our heart beats so there is a constant stream of fresh blood and nutrients reaching all the cells in our bodies.
A blockage in either a retinal vein or artery is medically known as a 'retinal vessel occlusion'. Occlusion means closing or blocking up. They can happen in any of the blood vessels in the body, including the retinal arteries and veins. A retinal vessel occlusion can affect sight.
Causes of retinal vessel occlusion
The main cause of a retinal artery occlusion is atherosclerosis. Atherosclerosis is a problem with the condition of the inside of the blood vessel's wall. If you imagine a blood vessel like a tube with the blood flowing through it then atherosclerosis is a problem with the inside of the tube. The tube is usually wide and smooth so that the blood flows directly through it. However in some people the inside of this tube becomes thinner or sticky which means it is harder for the blood to flow through it. These patches of sticky blood vessels are called atherosclerotic plaque, sometimes called hardening or thinning of the arteries and veins.Problems occur because these sticky patches can catch any debris in the blood which in turn makes the plaques bigger. If the plaques become bigger they can cut off part or all of the blood going to or from the retina. Large pieces of debris can also get caught and block off the blood vessel. This can then cause either a vein or an artery occlusion.
Risk factors for retinal vessel occlusion
There are a number of common risk factors for this thinning of arteries and veins. They are quite familiar since the problem of thinning arteries and veins can cause other problems like heart attacks and strokes. The main risk factors are :- Age - most retinal vessel occlusions happen in people over 65
- High blood pressure
- High cholesterol levels
- Diabetes
- Smoking
- Overweight.
Although nothing can be done about our age, all the other risk factors can be controlled. Regular visits to your GP to diagnose any circulation problems like high blood pressure and cholesterol levels, good diabetic control, a healthy diet and stopping smoking can all help to reduce the risk of experiencing a retinal vein occlusion.
Difference between artery and vein occlusions
Retinal artery occlusion
The retinal cells need a constant supply of fresh blood to keep working properly. If the arteries become blocked then this fresh blood cannot reach the cells as it should. When this happens the retinal cells quickly suffer from the lack of fresh oxygen. This stops them working and sight can be affected quite badly. The amount of sight that is affected varies according to the location of the blockage.Imagine the blood vessels spreading across the retina like a tree. Thinking of them like this can help to understand how much sight is affected by an artery occlusion. The retinal arteries have a large trunk of a blood vessel that splits into smaller branches to feed all parts of the retina. If the trunk of the tree is blocked then a lot of sight will be affected, less sight will be affected if the blockage happens further along in one of the branch arteries.
Retinal vein occlusion
The retinal veins drain away the used blood from the retinal cells. When one of these veins becomes blocked then the used blood cannot drain away properly. This causes the blood to 'back up' in the system. This blocking and pooling of blood can cause the area to swell and may also cause areas of haemorrhage (bleeding). These areas of swelling and backed up blood damage the cells of the retina and therefore damage sight. Again, the extent of the sight loss depends on where the blockage takes place.Treatment
Unfortunately, there is no treatment that can consistently restore vision lost from an artery occlusion. However, if it is caught within the first hour and treatment is initiated immediately, recovery is possible in rare cases.The following conditions increase the risk of problems that may affect the vessels of the eye : -
- High cholesterol
- Heart disease
- Arteriosclerosis
- Hypertension
- Diabetes
- Glaucoma
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