Introduction

Diabetic retinopathy is one of the most common causes of blindness in the UK. Retinopathy means damage to the tiny blood vessels (capillaries) that nourish the retina, the tissues in the back of the eye that deal with light. Damage to these vessels causes blood leakage (haemorrhage), which may be small and confined to the retina, or may extend forward into the jelly that fills the main cavity of the eye (the vitreous gel). This can seriously affect your vision.

Another feature of diabetic retinopathy is that new, fragile blood vessels grow on the surface of the retina, particularly around the head of the optic nerve (the optic disc). These new vessels bleed easily.

The main cause of diabetic retinopathy is diabetes. It can occur as a result of all types of diabetes, and if left untreated can lead to blindness.

It is important to have regular routine eye examinations because if new blood vessel formations are detected early, they can be treated effectively. Any new blood vessels can be dispersed by applying multiple laser burns to the periphery (outside edges) of the retina.

There are three main types of diabetic retinopathy:

• Background retinopathy - is the least serious type of retinopathy to affect your eye sight, but should still be regularly monitored by your GP or eye specialist (ophthalmologist). If you have background retinopathy, small red dots will appear on your retina due to tiny swellings in the blood vessel walls. Proteins in the blood may also lead to small yellow patches developing on the back of your eye.

• Pre-proliferative retinopathy - is when your retina swells and leaks blood. This can start to your obstruct vision, for example reading small print may become particularly difficult.

•  Proliferative retinopathy - rarely causes symptoms until it is too late. Symptoms, such as blurred vision, are likely to indicate that severe vitreous bleeding has developed, usually causing a sudden loss of vision.

Symptoms

Although diabetic retinopathy is entirely painless, it often causes sudden blindness. It does this when the fragile new blood vessels bleed into the vitreous gel (jelly that fills the eye). This appears as a dark cloud within your eye which can obscure your vision. The blood may slowly be absorbed, so that after a period of time - sometimes weeks or months - your vision may be restored.

Other symptoms of diabetic retinopathy can include:

tiny dots appearing in your vision,dark streaks appearing, sometimes blocking your vision,blurred vision,poor night vision, andhaving difficulty adjusting to bright, or dim, light.Severe bleeding into the vitreous gel can lead to the growth of new blood vessels and fibrous strands. This can be very serious because these fibrous strands can contract and pull off the retina - a form of retinal detachment that is difficult to correct. Treatment can sometimes repair this damage but, in other cases, blindness may be permanent.

Causes

Diabetic retinopathy is caused by diabetes. You are more likely to develop diabetic retinopathy if you do not control your diabetes closely.

Having a high blood sugar level and high blood pressure can cause your blood flow to increase. This thickens a membrane in your eye, preventing the flow of essential fluids in and out of your retina. Damaged cells then begin to release special chemicals that encourage the formation of new blood vessels. These new blood vessels tend to leak more fluid.

If left untreated, these growing vessels will begin to obscure your vision and perhaps lead to complications within the eye structure.

You are at increased risk of diabetic retinopathy if:

you have high blood sugar levels - when you have increased blood sugar levels for a prolonged period of time,you have been diabetic for a long time and take regular insulin treatment,you have high cholesterol levels, a high level of a fatty acid called triglyceride in your blood,you have high protein levels in your urine, you have high blood pressure.

Diagnosis

Diabetic retinopathy is diagnosed by an ophthalmologist (eye specialist) who will look at the back of your retinas using an ophthalmoscope (an instrument with a light on it which is used to inspect the inside of your eye).

If you have diabetic retinopathy, you may have some typical characteristics including:

yellow patches of fatty deposits, tiny dark dots called microaneurysms, and new blood vessels which have grown on your retina.If severe bleeding has occurred, the retina may not be visible. However, a diagnosis can still be made if you are known to have diabetes.

If you are diabetic you should always have regular (a minimum of yearly) eye tests to check for bleeding and abnormal blood vessel growths. The earlier you are diagnosed with diabetic retinopathy, the more effective treatment is likely to be. You will then be referred to an ophthalmologist (eye specialist) for further tests.

As part of your eye examination your ophthalmologist may perform a procedure to identify leaking blood vessels called fluorescein angiography. A dye will be injected into a vein in your arm that will eventually circulate to your eye making it easy to see blood vessels in your retina. This helps to locate areas over your retina that have become broken or are leaking fluid.

Your ophthalmologist may also request an Optical Coherence Tomography (OCT) examination. This is a non-intrusive procedure that scans your retina to provide images that highlight the thickness of your retina.

Treatment

Treatment for diabetic retinopathy will vary depending on which particular type you have:

Background retinopathy - requires no treatment, but you should have regular eye examinations by your GP or ophthalmologist (eye specialist) to spot any developments of the condition early.

Pre-proliferative retinopathy - often this also does not require treatment, but laser treatment can be an option if leakage begins to threaten your vision. Laser treatment cannot restore any lost vision, but can be used to prevent further deterioration.

Proliferative retinopathy - laser treatment is used to 'burn' the abnormal blood vessels to prevent further growth. The laser treatment does not target the blood vessels directly, but destroys those around your retina that have become starved of oxygen.Your GP will refer you to a specialist who can discuss all the options with you, including the benefits and any associated risks of laser treatment or eye surgery.

Laser treatment

Ophthalmologists often use lasers to treat diabetic retinopathy. The new blood vessels themselves are never directly burnt by laser. Instead, multiple laser burns are applied to the periphery (outside edge) of your retina, destroying large areas of your outer retina. These areas are much less important for vision than the central areas. When the retina has been made smaller, it needs less blood and the new blood vessels usually disappear.

Eye surgery

In rare cases, eye surgery may be considered if there is severe bleeding into your eye. This is usually the case if proliferative retinopathy has been diagnosed at a late stage. Eye surgery may also be an option if laser treatment has proved ineffective.

Complications

When blood vessels grow within your retina, they sometimes burst, or leak fluid. This can interfere with the normal blood flow to your eye, and may lead to complications. The main complications of diabetic retinopathy are:

Bleeding in the eye (vitreous haemorrhage) - if the bleeding from new blood vessels is small, you may only have temporary spots inferring with your vision. However, in more serious cases, blood may completely fill your eye blocking your vision completely. This bleeding does not cause permanent vision loss, and often clears up after a few week or months.

Traction retinal detachment - is where part of your eye is pulled out of its normal position. This happens as a result of scar tissue that forms at the back of your eye after the new blood vessels have grown. When the scar tissue shrinks, it pulls the retina away from the wall of your eye causing blank or blurred vision. In severe cases, this can cause complete loss of vision.

Neovascular glaucoma - alongside the leaking of blood vessels and abnormal growth of new vessels in your retina, you may also experience abnormal blood vessel growth within your iris (the coloured part of the eye that controls the amount of light that enters). This can disrupt the normal flow of fluids in your eye causing pressure to build up, potentially leading to damage to your optic nerves and, in severe cases, can cause permanent damage to your vision.

Prevention

To prevent, or slow, the progression of diabetic retinopathy, there are several aspects of your lifestyle that you may need to alter. For example, poor control of your diabetes can increase your risk of developing diabetic retinopathy. Therefore, it is important to:

Control your blood sugar levels - by keeping them as close to normal as possible. Ideally you levels should be between 90 and 130 milligrams per decilitre (mg/dL) before meals, and 180 mg/dL two hours after eating. This can involve taking medication such as insulin, eating a healthy diet, doing regular exercise, and controlling your weight.

Make sure you have annual eye examinations - tell your GP or specialist of any changes in your eye sight, particularly if you begin to experience blurred or spotty vision over the course of a few days. You GP will be able to check whether or not this is related to your blood sugar levels.

Stop smoking - particularly if you have diabetes, as it can narrow your blood vessels, and increase your chances of developing possible complications.

Ensure that your blood pressure and cholesterol levels are regularly checked - maintain a healthy, balanced diet, including plenty of fruit and vegetables (at least five portions a day), and make sure that you take regular exercise (at least 30 minutes, a minimum of 3-4 times a week). You should also restrict your alcohol intake as this will have an affect on your blood pressure (the recommended daily amount is between 3-4 units for men and between 2-3 units for women).In most cases, sight loss caused by diabetic retinopathy can be prevented if it is diagnosed early. Because your vision is not usually affected by diabetic retinopathy until the condition is at an advanced stage, regular eye checks are very important. Although your vision may be good, changes can be taking place within your retina that can be easily treated. Therefore, early diagnosis is vital.

The National Screening Programme for Diabetic Retinopathy offers regular (yearly) eye tests designed to detect diabetic retinopathy in everyone with diabetes over the age of 11. The test involves:

testing your vision,examining the back of your retina, and taking photographs of your retina to use in comparison to previous examinations.Eye drops are used as part of the test which can cause blurred vision for up to six hours afterwards. As your vision will be affected, you will need to arrange for a relative, or friend, to drive you home after the test.