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HEALTHWATCH

Diabetes and the eye

Diabetes can cause complications which can affect different parts of the body, the eye being one of them, says Dr. R. PREMA.


DIABETES is a disease that occurs when the pancreas does not secrete enough insulin or the body is unable to process it properly. Insulin is the hormone that regulates the level of sugar (glucose) in the blood. Diabetes can affect children and adults.

Diabetes can start in childhood, but, most 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:

This can also be referred to as Insulin Dependant 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:

This can also be referred to as Non-Insulin Dependant 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. This type of diabetes is generally controlled by diet or tablets, although some people in this group will use insulin injections.

Diabetes is a chronic disease that interferes with the body's ability to use and store sugar and can cause many health problems, including complications that affect many parts of the eye:

Diabetes can affect the eyes and vision in a number of ways.

Abnormal visual symptoms — fluctuating or blurring of vision, occasional double vision, loss of visual field, flashes and floaters

Early onset of presbyopia — the inability to focus on close objects

  • Cataracts
  • Glaucoma
  • Strabismus — a lack of eye muscle coordination
  • Decreased corneal sensitivity
  • Diabetic retinopathy
  • Ischemic optic neuropathy
  • Recurrent corneal erosions
  • Dry eye
  • Chronic eye infections
  • Disturbances in colour vision
  • Reduced peripheral vision
  • 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.

    Cataract

    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 involves a procedure to remove the cloudy lens, which is usually then replaced by a plastic lens, helping the eye to focus properly once again.

    Diabetic retinopathy

    The retina is the layer at the back of the eye that is sensitive to light. Diabetes affects the small vessels of the retina in the eye. There are various stages of diabetic retinopathy:

    Macular edema

    Non-proliferative or background diabetic retinopathy:

    When blood vessels in the retina are damaged, they can leak fluid or bleed. This causes the retina to swell and form deposits called exudates. This is an early form of diabetic retinopathy and may not lead to any decrease in vision, but it can lead to other more serious forms of retinopathy that affect the vision.

    Proliferative diabetic retinopathy

    Sometimes, diabetes can cause the blood vessels in the retina to become blocked. If this happens, then new blood vessels form in the eye. This is nature's way of trying to repair the damage so that the retina has a new blood supply.

    Unfortunately, these new blood vessels are weak. They are also in the wrong place — growing on the surface of the retina and into the vitreous jelly. As a result these blood vessels can bleed very easily and cause scar tissue to form in the eye. The scarring pulls and distorts the retina. When the retina is pulled out of position this is called retinal detachment. This condition is rarer than background retinopathy and is more often found in people who have been insulin dependent for many years. The new blood vessels will rarely affect your vision, but their consequences, such as bleeding or retinal detachment can cause your vision to get worse suddenly.

    Your eyesight may become blurred and patchy as the bleeding obscures part of your vision. Without treatment, total loss of vision can happen in proliferative retinopathy.

    With treatment, most sight-threatening diabetic problems can be prevented if caught early enough.

    The importance of early treatment

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

    Do not wait until your vision has deteriorated to have an eye test.

    Your family doctor, diabetologist or ophthalmologist can examine for diabetic retinopathy.

    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 by glasses.

    You might not know that you are having diabetic retinopathy, as there are no symptoms in the earlier stages of the disease.

    To detect retinopathy, your vision is assessed by the usual charts. The back of your eye examined after dilating your pupils using an instrument called an ophthalmoscope. Sometimes your ophthalmologist may advise a special test called Fundus Fluorescein Angiography.

    Laser treatment

    Most sight-threatening diabetic problems can be prevented by laser treatment if it is given early enough. It is important to realise however that laser treatment aims to save the sight you have and not to make it better. The laser, a beam of high intensity light, can be focused with extreme precision. So 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. In eight out of 10 cases, laser treatment causes the new blood vessels to disappear.

    All treatment is carried out in an outpatient clinic and you will not have to stay in hospital. Eye drops are used to enlarge the pupils so that the doctor can look into your eye. The eye is then numbed with drops and a small contact lens is put onto your eye to stop it from blinking. The eyes need to be moved in certain directions but this can easily be done with the contact lens in place.

    The treatment for sealing blood vessels doesn't usually cause any discomfort. However the treatment to remove new blood vessels can be a bit uncomfortable so you may be given a pain-relieving tablet at the same time as the eye drops. If the treatment does become painful, then it is possible to have an injection around the eye to numb the pain. Don't be afraid to ask for this injection, especially if you have found a previous session of laser treatment distressing.

    The treatment for sealing blood vessels has few side-effects, although you may lose a little central vision or notice the laser burns as small blank spots.

    The laser treatment to remove new blood vessels is more complicated and there may be more side effects. It is quite common to lose some vision to the sides (peripheral vision), and this may mean that you will not be able to drive in future. Night and colour vision may also be reduced. Occasionally your central vision may not be as good as before so that print isn't as easy to see. This is usually temporary, but sometimes this doesn't improve.

    No treatment is possible without some side-effects. But the risks of laser treatment are far less than the risks of not having treatment.

    The laser is very bright and causes a temporary reduction of sight which may last an hour or two after treatment. Most people have a headache after the more lengthy treatment and you can take a headache tablet for this. However if the pain is severe, or if your eyesight gets worse, you should contact your consultant straightway.

    If your eye condition becomes more severe, causing retinal detachment and scar tissue, it may be possible to perform vitreous surgery. This is highly specialised and you should discuss the various options with a consultant ophthalmologist.

    The longer the person has diabetes, the greater are his/her chances to develop diabetic retinopathy. Almost 80 per cent of people, who have diabetes for 15 years or more, have some damage to the blood vessels in their retina. The other risk factors are high blood pressure, anaemia, kidney diseases, and pregnancy.

    There is no treatment that can prevent diabetic retinopathy altogether. Persons with any form of diabetes may develop diabetic retinopathy. But it has been proven that a good control of diabetes can delay and slow down the rate of progress of diabetic retinopathy and its complications. Besides good control of blood sugar, one must exercise regularly, keep blood pressure under control, avoid smoking, and not be obese.

    If fundus examinations are initiated prior to the development of significant retinopathy, then repeated periodically, and if the recommendations of Early Treatment Diabetic Retinopathy Study (ETDRS) are followed with respect to the management of diabetic macular oedmea and/or neovascularization, the risk of severe visual loss is less than five per cent

    The next predictor of diabetic retinopathy is the duration of the disease. Patients who have had IDDM for five years or less rarely show any evidence of diabetic retinopathy. However 27 per cent of those who have had diabetes for five to 10 years and 71-90 per cent of those who have had diabetes for longer than 10 years have diabetic retinopathy. After 20-30 years, the incidence rises to 95 per cent and about 30-50 per cent of these patients have (PDR) Proliferative Diabetic Retinopathy.

    The diabetes control and complications trial showed emphatically that patients who closely monitored their blood glucose (four measurements/day, which is equivalent to tight control) do far better than patients treated with conventional therapy (One measurement/day). The former had a 76 per cent reduction in the rate of development of any retinopathy and an 80 per cent reduction in progression of established retinopathy versus those with conventional control. For advanced retinopathy however, even the most rigorous control may not prevent progression.

    Renal disease as evidenced by proteinuria, elevated blood urea nitrogen increased blood creatinine is an excellent predictor of the presence of retinopathy. Even patients who have microalbuminuria are at high risk of developing retinopathy.

    In diabetic women, who begin a pregnancy without retinopathy, the risk of developing non-proliferative diabetic retinopathy is about 10 per cent. Further those, with non-proliferative diabetic retinopathy at the onset of pregnancy and those who develop systmic hypertension tend to show progression with increased haemorrhage, cotton wool spots and macular oedema and no doubt exists that women who maintain good metabolic control during pregnancy, have fewer spontaneous abortions and fewer children with birth defects. However women who begin pregnancy with poor control but who then are suddenly brought under strict control, frequently have severe rapid worsening of their retinopathy and do not always recover after delivery.

    All diabetics need to have a thorough eye examination shortly after the diagnosis.

    Insulin dependent diabetics then require eye exams every two years.

    By eight years after diagnosis, yearly exams become necessary.

    Non-insulin dependent diabetics require exams yearly.

    Women with diabetes who become pregnant need an exam in their first trimester, and likely another one at the start of their third trimester. The presence of proteinuria is cause for immediate assessment. Your doctor may make recommendations that are different from these.

    * * *

    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.

    * * *

    Things to tell your eye doctor

  • The type of diabetes you have, Type I or Type II
  • How long you have had it.
  • If you have family members with diabetes or eye problems.
  • How you control the diabetes with diet, pills, or insulin.
  • If vision is fluctuating.
  • Typical value and range of self-monitored blood glucose level.
  • Name of your family doctor.
  • List of all medications you take, prescription or otherwise.

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