Types of diabetic eye disease

There are 3 sight-threatening forms of diabetic retinopathy:

• Proliferative diabetic retinopathy. Diabetes damages and blocks blood vessels that supply the retina. This can reduce the supply of oxygen to the retina, stimulating the growth of new blood vessels, a process called retinal neovascularisation or proliferative diabetic retinopathy.
• Diabetic macular oedema (or diabetic macular edema; DME) occurs when glucose damage leads to swelling in the macula, the central zone of the retina. The macula has a higher concentration of photoreceptor cells than any other part of the retina and this provides fine focus and high visual acuity. Even slight macular swelling leads to blurred vision.

Cataracts develop when the lens of the eye becomes clouded. Cataracts are 6 times more common in patients with diabetes.

Diabetic retinopathy and diabetic macular oedema

Diabetic retinopathy has several stages with symptoms that range from mild to severe.

Mild non-proliferative diabetic retinopathy is the mildest form. The underlying damage to the blood vessels to supply the retina with nutrients and oxygen start to show signs of damage.

Tiny swellings or microaneurysms start to appear as the blood vessel walls weaken.

You probably won’t have symptoms at this point, but the changes will be obvious to a health professional who examines your eyes using an ophthalmoscope.

In the next stage, moderate non-proliferative diabetic retinopathy, some of the blood vessels degenerate completely in places, causing blockages. There are only a few at this stage, but as many more become clogged and unable to carry blood, the disease progresses to severe non-proliferative diabetic retinopathy.

In this stage, the blood supply to the retina is reduced, so parts of it become short of oxygen, or ischaemic to use the medical description.

The development of ischaemia is a turning point in diabetic retinopathy as this results in signals that encourage the growth of new blood vessels to supply the oxygen that is lacking.

Non-proliferative retinopathy becomes proliferative diabetic retinopathy as new blood vessels proliferate from the network under the retina. Not only do these new blood vessels grow randomly, sometimes growing through the retina and into the vitreous of the eye, they are not well-formed and are usually liable to split and bleed. Significant bleeds into the eye can cause sudden loss of vision.

The general build-up of excess fluid in the retina can also cause swelling between the layers of cells. If this happens in the macula, the central point of the retina, diabetic macular oedema develops. Although diabetic macular oedema can happen even in early non-proliferative diabetic retinopathy, it becomes more likely in the later stages of this diabetic eye disease.

Preventing diabetic eye disease and vision loss

Tight control of blood glucose, coupled with control of blood pressure and blood cholesterol can help reduce the risk of developing diabetic retinopathy and diabetic macular oedema. Regular eye screening and prompt treatment are also essential to prevent vision loss.

Controlling diabetes

Large studies on hundreds of people with type 1 diabetes and type 2 diabetes have shown that diabetic retinopathy is more likely if your diabetes is not well controlled. If you can control your blood glucose levels within tight limits, and avoid hyperglycaemia and hypoglycaemia, you can reduce your risk of diabetic retinopathy and diabetic macular oedema, as well as lowering the chances that you will develop diabetic kidney disease or neuropathy.

Keeping your blood glucose under control is important, as keeping your blood pressure down – below 130/70 if possible – and having your blood cholesterol checked to make sure it is within the normal limit.

Regular diabetic eye screening

This is essential because sight-threatening eye disease typically has no symptoms. It is possible to develop proliferative diabetic retinopathy, or diabetic macular oedema, or BOTH conditions at the same time and have no symptoms at all. Your vision may be unaffected one day, but could be seriously impaired the next, with no warning at all.

Every type of diabetic eye disease can be detected in its earliest stages by a careful examination of the front of the eye (the cornea and lens) and the retina and macula at the back of the eye.

If you are resident in the UK, you will be offered a free annual photographic eye screen under the NHS diabetic eye disease screening service.

The photographs are usually checked by technicians. The eye centre at The London Clinic offers individual assessments by a consultant retinal specialist.