What is diabetes mellitus?
Diabetes mellitus is a common disease in many countries. In Singapore, about 9% of the population has diabetes mellitus.
Most patients with diabetes have non-insulin-dependent diabetes mellitus (NIDDM), also called adult-onset or Type II DM. For these people, control of their blood sugar can generally be achieved with oral medication or in some cases, dietary restrictions alone.
Insulin-dependent diabetes mellitus (IDDM), also known as juvenile-onset or Type I diabetes, is less common. IDDM patients require regular insulin injections to control their blood sugar levels.
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Who gets diabetic retinopathy?(1 in 5 diabetics are affected)
Diabetes mellitus damages small blood vessels throughout the body, affecting many organs e.g. the kidneys, nerves, brain and retina. Damage to the small blood vessels supplying the retina results in diabetic retinopathy, which is a major cause of blindness in many countries.
All patients with diabetes are at risk of developing diabetic retinopathy. However, IDDM patients are at greater risk due to earlier onset of disease. In a screening exercise for diabetic retinopathy in Singapore, 22% of patients were found to have retinopathy; and about half of these patients had severe, sight-threatening disease. This makes diabetic retinopathy a common condition in Singapore.
Although retinopathy is strongly related to duration of diabetes, it starts earlier and is more severe in those with poorly controlled disease. When combined with other medical problems (e.g. high blood pressure and kidney disease), or even pregnancy, the risk of retinopathy is even higher. Hence, good control of blood sugar levels as well as other medical problems is of great importance in all diabetics
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What are the different stages of diabetic retinopathy?
Diabetic retinopathy is divided into 2 stages based on severity:
1. Nonproliferative diabetic retinopathy (NPDR)
2. Proliferative diabetic retinopathy (PDR)
In addition, the involvement of the centre of the retina, the macula, by fluid accumulation and swelling may accompany NPDR and PDR. This is called macular edema, and can cause early reduction in central vision, thereby impairing reading and sharp distance vision.
1. Nonproliferative diabetic retinopathy (NPDR)
This is the early stage of diabetic retinopathy. The damaged retinal blood vessels leak fluid and blood into the surrounding retina. In addition, there is reduced blood circulation to the area normally supplied by these vessels, starving the retinal cells of oxygen and other nutrients.
At this stage, unless the macula is involved, vision may still be good.
2. Proliferative diabetic retinopathy (PDR)
PDR is the advanced stage of retinopathy, and is a major cause of blindness in diabetics.
This develops as retinal cells are increasingly starved of oxygen and the eye attempts to produce new blood vessels to compensate for this deficiency. Unfortunately, these blood vessels are abnormal and prone to breaking, which can result in bleeding into the eye. This blood results in poor vision and hinders treatment.
In addition, scar tissue accompanies the growth of the abnormal blood vessels and can pull on the retina and cause retinal detachment.
Abnormal vessels may also grow on the iris and angles and cause accumulation of fluid within the eye. The raised pressure within the eye as a result of this fluid accumulation is called “rubeotic glaucoma”.
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How will the eye doctor examine me for diabetic retinopathy?
Regular eye examination is important in all diabetics, including those with good control of sugar levels. Early diagnosis and treatment can significantly slow down the progression to sight-threatening disease.
The examination will involve checking the iris for abnormal vessels, and measuring the pressure of the eye. The pupils will then be dilated so that the retina can be examined in detail using various lenses and instruments. Pupil dilatation may cause mild and temporary blurring of vision.
In selected cases, a special test called fluorescein angiography may be done to help in diagnosis and treatment. The test involves injecting a fluorescent dye into a vein in the hand or forearm, and taking photos of the retina as the dye travels to the retinal blood vessels and lights up abnormal areas.
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How can diabetic retinopathy be treated?
Good control of blood sugar levels with medication and dietary restriction is the most important step in delaying the onset and slowing down the progression of diabetic retinopathy.
1. Laser therapy
Once potentially sight-threatening retinopathy develops, laser therapy will be required. Very often, more than one session will be required for complete treatment. This treatment is generally done on an outpatient basis under local anesthesia.
It is important to understand that the benefits of laser therapy will not be immediately apparent. In fact, laser treatment may sometimes cause vision to worsen temporarily. Even where improvement in vision is expected, the effect may be seen only after weeks or months.
Side effects of laser therapy may include shrinkage of the peripheral visual field, decreased night vision and reduced color vision. However, in advanced diabetic retinopathy, the benefits of laser therapy in reducing the risk of permanent and severe visual loss far outweigh the side effects.
2. Surgery
In retinopathy too severe for laser therapy alone to be effective, or where end-stage complications (e.g. retinal detachment) have occurred, surgery may be the only treatment option. Surgery will include vitrectomy (removal of the jelly of the eye), and may be accompanied by other procedures like laser therapy at the time of surgery, surgical peeling of fibrous tissue and re-attachment of detached retina, etc. A gas bubble or silicon oil may be left in the eye after surgery. While the gas bubble will disappear over several weeks, silicon oil may need to be removed in a second operation after the disease is observed to have stabilized.
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How can diabetic retinopathy be prevented?
By following these simple guidelines, one can reduce the risk of visual loss from diabetic retinopathy:
1. Blood sugar levels should be well controlled with dietary restriction and/or medication.
2. Other medical problems like high blood pressure should be controlled.
3. Screening for retinopathy should start within 5 years of the diagnosis of the diabetes mellitus.
4. Diabetics should be screened for accelerated retinopathy during pregnancy.
5. Eye examination should be done at least once yearly in diabetics who do not have retinopathy yet.
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