What is diabetes?

Diabetes mellitus is a condition which due to a lack of insulin, the body cannot cope normally with sugar and other carbohydrates in the diet.

Diabetes can start in childhood, but more often begins in later life. It can cause complications which affect different parts of the body, the eye being one of them. There are two different types of diabetes mellitus:

Type 1 diabetes, which can also be referred to as insulin dependent diabetes mellitus (IDDM). This type of diabetes commonly occurs before the age of 30 and is the result of the body producing little or no insulin. Type 1 is controlled by insulin injections.

Type 2 diabetes, which can also be referred to as non-insulin dependent diabetes mellitus (NIDDM). This type of diabetes commonly occurs after the age of 40. In this type of diabetes the body does produce some insulin, although the amount is either not sufficient or the body is not able to make proper use of it. Type 2 diabetes is generally controlled by diet or tablets, although some people in this group will use insulin injections.

Why annual eye examinations are important

If you have diabetes this does not necessarily mean that your sight will be affected, but there is a higher risk. If your diabetes is well controlled then you are less likely to have problems, or they may be less serious. However, if there are complications that affect the eyes then this may result in loss of sight.

Most sight loss due to diabetes can be prevented, but it is vital that it is diagnosed early. This can only be detected by a detailed examination of the eye. Therefore, regular, annual eye examinations are extremely important, as you may not realize that there is anything wrong with your eyes until it is too late.

How the eye works

In understanding how diabetes can affect the eye, it is worth looking at how the eye works.

Your eye has a lens and an aperture (opening) at the front known as the pupil, which adjust to bring objects into focus on the retina at the back of the eye. The retina is made up of a delicate tissue that is sensitive to light, rather like the film in a camera. It also contains a fine network of small blood vessels.

At the centre of the retina is the macula, which is a small area about the size of a pinhead. This is the most highly specialised part of the retina and is vital because it allows you to see fine detail for activities such as reading and writing and also to recognise colours. The other parts of the retina give you side vision (peripheral vision). Filling the space in front of the retina is a clear jelly-like substance called the vitreous gel.

How can diabetes affect the eye?

Diabetes can affect the eye in a number of ways. The most serious eye condition associated with diabetes involves the retina, and, more specifically, the network of blood vessels lying within it. The name of this condition is diabetic retinopathy. Diabetic retinopathy is usually graded according to how severe it is. The three main stages are described below.

What can I do to reduce the risk of sight loss from diabetes?

It has been shown that excellent control of diabetes significantly reduces sight threatening complications. It is also important to monitor and treat high blood pressure. Maintaining excellent diabetic control and normal blood pressures are the two main things that you can do to prevent visual loss from diabetes.

Your diabetic clinic, GP or hospital can monitor your blood pressure at your regular check ups. High blood pressure can usually be helped by lifestyle changes and medication. Your doctor would be able to discuss with you what would be best in your case.

Nerve damage, kidney and cardiovascular disease are more likely in smokers with diabetes. Smoking increases your blood pressure and raises your blood sugar level which makes it harder to control your diabetes.

Not smoking, good sugar, blood pressure and cholesterol control can all reduce the risk of diabetes related sight loss.

The importance of early treatment

Although your vision may be good, changes can be taking place in your retina that need treatment. Because most sight loss due to diabetes is preventable, remember:

  • early diagnosis of diabetic retinopathy is vital
  • have an eye examination every year
  • do not wait until your vision has deteriorated to have an eye test
  • the importance of early treatment of diabetic retinopathy cannot be stressed enough

Your optometrist can examine your eyes for diabetic retinopathy. In some cases photographs of the retina are used to detect abnormalities without any other form of test. If a problem is found you will be referred to a consultant ophthalmologist.

Remember, however, that if your vision is getting worse, this does not necessarily mean you have diabetic retinopathy. It may simply be a problem that can be corrected with glasses.

What is the treatment?

Most sight-threatening problems caused by diabetic retinopathy can be managed by laser treatment if it is given early enough. It is important to realise, however, that laser treatment can only preserve the sight you have – not make it better. The laser, a beam of high intensity light, can be focused with extreme precision so that the blood vessels that are leaking fluid into the retina can be sealed.

If new blood vessels are growing, more extensive laser treatment has to be carried out.

Other ways diabetes can affect the eyes
Temporary blurring

This may occur as one of the first symptoms of diabetes although it may also occur at any time when your diabetes is not well controlled. It is due to a swelling of the lens of the eye and will clear without treatment soon after the diabetes is brought under control again.


A cataract is a clouding of the lens of the eye, which causes the vision to become blurred or dim because light cannot pass through the clouded lens to the back of the eye. This is a very common eye condition that develops as people get older but someone with diabetes may develop cataracts at an earlier age than someone without diabetes. The treatment for cataracts involves an operation to remove the cloudy lens, which is usually then replaced by a plastic lens, helping the eye to focus properly once again.

Important points to remember
  • Early diagnosis of diabetic retinopathy is vital.
  • Have an eye examination every year.
  • Do not wait until your vision has deteriorated to have an eye test.
  • Most sight-threatening diabetic problems can be managed by laser treatment if it is given early enough. Do not be afraid to ask questions or express fears about your treatment.
  • Good sugar, blood pressure and cholesterol control reduces the risk of diabetes related sight loss. Attend your diabetic clinic or GP surgery for regular diabetes health checks, including blood pressure and cholesterol monitoring.
  • Smoking increases your risk of diabetes related sight loss. Your GP can tell you about NHS stop smoking services in your area.