The most serious eye condition associated with diabetes involves the light sensitive membrane at the back of the eye called the retina. More specifically, it involves the network of blood vessels within the retina. This condition is called diabetic retinopathy.
Diabetic retinopathy is usually graded according to how severe it is. The three main stages of diabetic retinopathy are:
- Background diabetic retinopathy
- Diabetic maculopathy
- Proliferative diabetic retinopathy
Background diabetic retinopathyThis is an early stage of diabetic retinopathy. The blood vessels are only mildly affected. They may bulge slightly (micro-aneurysms), they may leak fluid or fats and proteins (exudates) or they may break and bleed. The central area of the retina, called the macula, remains unaffected so vision remains normal.
Diabetic maculopathyIf the background retinopathy becomes more severe with time, the macular area of the retina may become involved. The macula is the central part of the retina that is responsible for sharp vision ie. reading and distinguishing faces and for colour vision. If diabetes affects this area it is termed maculopathy.
There are two ways in which diabetes can affect the macula:
- Macular oedema
- Macular ischaemia
The central retina becomes swollen due to leakage of fluid from the small blood vessels that supply the macula. It is the most common cause of visual loss in diabetes. Vision loss may vary from mild to severe, but even in the worst cases, side vision continues to function. This side vision allows you to get around at home or outside.
This occurs when the small blood vessels that supply the macula, called capillaries become blocked. Vision blurs because the macula no longer receives sufficient blood supply to function properly.
Proliferative diabetic retinopathyIf the diabetic retinopathy becomes worse, blood vessels in other parts of the retina may become blocked. If this happens, abnormal new blood vessels form in an attempt to supply blood to the area where the original vessels closed.
Unfortunately, the new blood vessels do not resupply the retina with normal blood flow. The vessels grow in the wrong place – on the surface of the retina and into the jelly substance, called the vitreous, that fills the cavity of the eye.
These blood vessels are associated with scar tissue that can pull on the retina and distort it. When the retina is pulled out of position it is called a retinal detachment. In addition, the blood vessels are fragile. These fragile vessels may bleed into the vitreous resulting in a vitreous haemorrhage. If the vitreous haemorrhage is small, a person may only see a few dark floaters in the eye. If a vitreous haemorrhage is large however, it may block out all vision.
It may take days or even months to clear the blood, depending on the amount of blood present. If the eye does not clear the vitreous blood adequately within a reasonable time, an operation called a vitrectomy, where the jelly substance is removed from the eye, may be recommended.
Occasionally, widespread retinal blood vessel closure will result in abnormal blood vessels growing on the iris, the coloured part of the eye. These blood vessels can block the drainage channels of the eye resulting in raised pressure in the eye. This is called neovascular glaucoma. Neovascular glaucoma is a severe eye disease that can result in damage to the optic nerve.
How is diabetic retinopathy diagnosed?Your eye doctor will look through the pupil with a special instrument and examine the retina. If diabetic retinopathy is present, he or she may order colour photographs of the retina or a special test called a fluorescein angiogram. In this test, a coloured dye is injected into a vein in the arm and photographs of the back of the eye taken. The dye leaks out of any retinal blood vessels that are damaged.
How is diabetic retinopathy treated?Prevention is the best treatment. Strict control of your blood sugar level will significantly reduce the long term risk of vision loss from diabetes. If high blood pressure, high cholesterol levels and kidney problems are present, they need to be treated too.
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. It does not improve your vision. In some instances, laser may make the vision a little worse initially, but in the long term, it will help to stabilise your vision, preventing much worse vision loss in the future.
How is laser treatment carried out?Laser is a beam of high intensity light that can be focused very precisely. Eye drops are given to enlarge the pupil. Other drops are given to numb the surface of the eye. A special type of contact lens is placed on the surface of the eye. This allows the laser to be focused on the retina.
Laser treatment for macular oedemaFor macular oedema, the laser is focused on the retina near the macula to decrease the fluid leakage. The goal of treatment is to prevent further visual loss. It is uncommon for people who experience blurred vision from macular oedema to recover normal vision, although some may experience partial improvement after laser treatment. A few people will be able to see the laser spots near the centre of vision following treatment. These usually fade with time but may not disappear completely.
Laser treatment for proliferative diabetic retinopathyLaser treatment in proliferative diabetic retinopathy is directed at the peripheral retina away from the macula. This type of laser treatment is called panretinal photocoagulation. It causes the abnormal blood vessels to shrink, lessening the chance of vitreous haemorrhage and retinal detachment.
Multiple laser treatments may be required over time for both macular oedema and proliferative diabetic retinopathy. Laser does not cure diabetic retinopathy and cannot always prevent further loss of vision.
Is laser treatment painful?Laser treatment for macular oedema is not usually painful. Laser treatment for proliferative diabetic retinopathy however is more extensive and can be a bit uncomfortable. It is a good idea to take two 500mg paracetamol tablets (such as Panadol) half an hour before the treatment. If the treatment is still uncomfortable for you, a small injection can be given around the eye to numb it.
What are the possible complications of laser treatment?If laser treatment is recommended for you, the possible side effects of laser treatment will be far less than the risk of loss of vision without treatment.
Laser for macular oedema may result in temporary reduction of sight for some hours after the treatment. You may also lose a little of the central vision or be able to see the effects of the laser as small black spots in your vision. Colour vision may occasionally be affected.
Laser for proliferative diabetic retinopathy may result in some loss of peripheral or side vision. This may affect your ability to drive a car safely. Dr Hornsby will be able to perform a visual field test after the treatment to determine if your side vision is affected. Night vision may also be affected.
Occasionally, your central vision may not be as good as before. This is usually temporary, but occasionally does not improve.
If you have any concerns about the possible side effects of laser treatment, you should discuss these with your eye doctor.
Surgical treatment for diabetic retinopathyIn advanced diabetic retinopathy, your eye doctor may recommend an operation called a vitrectomy. During this procedure, the blood stained vitreous is removed and replaced with a clear fluid. Abnormal blood vessels are removed and laser is applied to the retina. If the retina is detached, it can be repaired during the surgery.
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