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Diabetes and Your Eye
- The Normal Eye
- How Diabetes affects your eyes
- Are you at risk?
- What can you do?
- Laser Treatment For Diabetic Retinopathy
- Other treatments for Diabetic Retinopathy
The Normal Eye [ top ]
The eye is like a camera. Light rays pass through the cornea, the lens and the vitreous to focus on the retina. The cornea is the window at the very front of your eye. The lens is behind the coloured part of your eye (iris). Cloudiness of the lens is called cataract. The vitreous is a jelly-like substance that gives the eyeball its shape and also helps keep the retina intact. Finally, the retina is the tissue at the back of the eye that picks up the light like the film of a camera and transmits it to the brain via the optic nerve. The central part of the retina, which does the straight ahead vision which is necessary for reading and driving, is called the macula.
How Diabetes affects your eyes [ top ]
With time, people with diabetes develop a condition of the retina called diabetic retinopathy. This is because, more than any other part of the body, the blood vessels of the retina are sensitive to even slight increases in blood sugar levels.
Background diabetic retinopathy
There are two stages of diabetic retinopathy. The early stage, or 'background' diabetic retinopathy, does not affect vision. Background diabetic retinopathy consists of abnormalities and bleeding of the retinal blood vessels.
Vision threatening diabetic retinopathy
Eyes with background diabetic retinopathy may progress to "vision threatening" retinopathy. The most common type of vision threatening retinopathy is due to swelling of the central retina (macular oedema) due to abnormal leakage from the blood vessels of the macula. If it involves the centre of the macula, macular oedema causes blurring of the vision which cannot be corrected by glasses. In the earlier stages however, macular oedema does not affect central vision and can only be detected by your eye doctor, even when it is threatening vision.
The other type of vision threatening retinopathy occurs when oxygen levels in the eye start to drop because of poor blood supply to the peripheral retina, causing new blood vessels to sprout from the normal retinal vessels and grow into the vitreous. This is called 'proliferative' diabetic retinopathy. These new blood vessels never do any good; they are fragile and tend to bleed, leading to loss of vision from vitreous haemorrhage and scarring inside the eye. The patient is only aware of these abnormal blood vessels when they start to bleed, in which case they are seen by the patient as black clouds, or 'floaters'.
Diabetes can also cause cataracts to form at an earlier age. Cataracts usually occur in older people, however in people with diabetes they may develop at a younger age. A cataract forms when the lens in the eye becomes opaque, so the light rays cannot reach the retina clearly. Some possible symptoms of cataracts are blurred vision, glare, focusing problems, decreased contrast and colour sensitivity.
Another eye condition that is related to diabetes is glaucoma. Glaucoma slowly damages the optic nerve at the back of the eye to deteriorate, and can eventually cause irreversible blindness. It can only be detected and treated by an ophthalmologist. The eye pressure needs to be measured, a visual field test performed and the appearance of your optic nerve needs to be assessed.
Proliferative diabetic retinopathy showing bleeding on the retinal surface from abnormal retinal vessels caused by diabetes |
Are you at risk? [ top ]
Anyone who has been diagnosed with diabetes has an increased risk of loss of vision, mainly from diabetic retinopathy but also from cataract and glaucoma.
What can you do? [ top ]
In general, laser treat of diabetic retinopathy can prevent loss of vision but it may not restore lost vision. This is why regular check ups are essential even when vision is normal so that your eye doctor can apply laser treatment when vision threatening retinopathy develops to prevent loss of vision.
Eye examinations should begin at the time you have been diagnosed with diabetes then you will be reviewed as directed by your ophthalmologist. People with no diabetic retinopathy are reviewed every two years. People with diabetic retinopathy are reviewed more frequently depending on the extent of the disease.
Keeping blood sugar levels as low as possible will help reduce the risk of developing diabetic retinopathy. Discuss with your GP the best ways to reduce blood sugar levels. If you are having difficulties it is a good idea to consider seeing an endocrinologist with a particular interest in diabetes. These specialists are also known as 'Diabetologists'.
The best measure of the blood sugar control is the 'glycosylated haemoglobin', or HbA1c. The results of this test, which measures the amount of glucose that attaches to your red blood cells over a three month period, is the strongest predictor we have of whether you will lose vision or not. You should set a target glycosylated haemoglobin level in consultation with your doctors and strive to achieve it. Unfortunately, a significant period of poor blood glucose control increases the risk of loss of vision for up to ten years even if you are able to bring your glycosylated haemoglobin to near normal levels. Diabetic retinopathy rarely goes away (sometimes it does in the early phases) even when blood glucose levels improve dramatically, but improving blood sugar levels reduces the risk of further progression.
The other risk factor that you can work on is high blood pressure. Even small reductions of blood pressure have a highly beneficial affect on your eyes for a prolonged period.
Who to see and what will happen [ top ]
Ophthalmologists (eye doctors) can assess your eyes to look for any signs of diabetic retinopathy and to ensure your eyes are healthy. You will need a referral to be seen by an Ophthalmologist; your GP, optometrist or specialist can provide this.
On arrival at your ophthalmologist's rooms, you will first be seen by an Orthoptist. The orthoptist will take a history, assess your vision, check your eye pressure, and instill dilation drops to enlarge the pupil, which takes at least another 30 minutes. This will cause your vision to go blurry and light sensitive for several hours after the consultation. It is advised not to drive for approximately two hours after the drops have been instilled and it is also recommended to bring sunglasses.
During your consultation, you may be advised to undergo a fluorescein angiogram. This test involves fluorescein dye, which is injected into the arm causing the dye to travel through the blood vessels to the eye where photos are taken for further assessment. There may be side effects, which will be explained thoroughly at the time. Fluorescein angiograms help the doctor identify the areas of blood leakage and facilitate laser treatment.
Laser Treatment For Diabetic Retinopathy [ top ]
Laser treatment, the standard treatment for diabetic retinopathy, can be highly effective in preventing loss of vision. The earlier it is used the better. Your eye doctor will put an anaesthetic eye drop in your eye, then insert a contact lens which will keep the eye still and stop you blinking. A tiny beam of light (one tenth to one half of a millimeter in diameter) is then used to selectively cauterise the diseased retina.
Laser treatment for diabetic macular oedema
Laser treatment for diabetic macular oedema is performed in one to two sessions, each of which takes 5-15 minutes. Between 5-100 burns will be applied. It is typically not painful, although it does dazzle the vision so you may not see anything from the treated eye for up to a couple of hours later (you should still be able to see because the treatment will not affect your other eye). The laser is applied to seal the leak, which usually stops the swelling.
You must try to keep your eyes still during the treatment. Your eye doctor may ask you to look directly at the red aiming beam at the start of the procedure in order to determine precisely where your reading centre is, but after that you should not look at the aiming beam because an accidental burn to the reading centre may destroy your central vision permanently. It is best to ignore what is going on in the eye being treated by keeping your other eye open and staring straight ahead. All this sounds difficult but it usually turns out to be easier than the patient expects.
Sometimes laser treatment itself can damage the central vision, particularly in patients with severe diabetic retinopathy who need multiple treatments. However, even when the side effects are taken into account, laser treatment is still highly effective because it reduces the risk of loss of reading and driving vision in eyes with vision threatening macular oedema from 1:3 without treatment, to 1:10 over a three year period. In other words you can still lose vision after laser treatment, it is just much less likely. It is not uncommon to meet patients who complain that their vision was normal until they had laser treatment then it got worse. Some are convinced that the laser treatment damaged the vision. More often the vision was going to get worse anyway (that is why they had the treatment in the first place) and the laser treatment did not stop it.
Diabetic macular oedema showing yellow material scattered throughout the central retina. This is fat which has leaked out of retinal blood vessels which have been damaged by diabetes |
Laser treatment for proliferative diabetic retinopathy
Laser treatment of proliferative diabetic retinopathy is a more extensive treatment, called 'pan retinal photocoagulation' (PRP), in which the diseased peripheral retina is destroyed. This is performed in two to four sessions per eye, with around 400 laser burns per session. This can be quite painful - some patients feel it more than others. If the pain is intolerable then a 'block' can be performed by injecting local anaesthetic behind the eye, but it is best to avoid this if possible.
Adverse events associated with PRP include reduced visual field and impaired night vision, sometimes (but usually not) to an extent that may impair your ability to drive. PRP does not improve central vision, sometimes it makes it a little worse. However, these adverse events rarely stop an eye doctor strongly recommending PRP to patients with proliferative diabetic retinopathy because once patients develop this condition they have a 50% chance of becoming blind over a five year period, PRP reduces this risk to only 5%.
Similar to macular oedema, laser treatment is ideally performed on proliferative diabetic retinopathy when the vision is still normal. If the treatment does not work the eye may still go blind - but that does not mean that the laser treatment caused the blindness. These eyes were going to go blind anyway and the laser treatment failed to prevent it.
Other treatments for Diabetic Retinopathy [ top ]
Prof Gillies' Retinal Therapeutics Clinical Research Group at the Save Sight Institute, University of Sydney, has performed pioneering Randomised Clinical Trials which have demonstrated for the first time that injections into the eye of the steroid triamcinolone can reverse loss of vision in eyes with diabetic macular oedema that does not respond to laser treatment. This intervention is described in Retinal Vein Occlusion
Surgical treatment, including removal of the vitreous (vitrectomy) in eyes with advanced diabetic retinopathy can also be helpful in advanced disease. These treatments will be discussed with you further by your eye doctor if appropriate.
If you have any concerns after laser treatment for diabetic retinopathy, you should contact your ophthalmologist.
