Diabetes mellitus is a common disease in which there is an increased level of glucose (sugar) in the blood of the affected person. There are nearly 6.2 crore people in India suffering from diabetes. A recent study by the Indian Council of Medical Research (ICMR) showed that 7.3% of adults aged 20 years and above have diabetes. So it is an important public health problem.
Types of Diabetes
1. Type I which develops in childhood and
2. Type II which develops usually after > 30 years of age.
Who is likely to develop diabetes?
• Some of the risk factors for the development of type II diabetes are –
• Obesity
• Sedentary life style
• High blood pressure
• Diabetes in parent/s and
• Higher economic status
However, diabetes is being increasingly seen in persons who are not obese and belong to low-income groups. Reducing the weight in obese persons, daily physical activity and control of high blood pressure reduce the chances of getting diabetes.
How does diabetes affect our body?
Diabetes over a period of time affects several organs that include kidneys, nerves, brain, eyes and heart leading to serious health problems in patients suffering from diabetes.
High level of sugar in the blood for years leads to changes in the small blood vessels. The walls of the small blood vessels become thicker which may lead to the closure of their lumen leading to a reduction of blood supply in the organ. A gradual process of small blood vessel closure leads to severe damage to organs like kidneys, heart, nerves, eyes and brain.
What damage does diabetes cause in the eyes?
The most important damage due to diabetes occurs in the thin layer of nervous tissue in the back of the eye called, Retina. The image shows, how the normal central part of the retina looks like with the optic nerve head or disc, macula and blood vessels labeled.
The retina is the light-sensitive neural tissue that detects the images of objects we see and transmits these images to the brain through the optic nerve. Apart from diabetic retinopathy, diabetes also causes earlier development of cataract, paralysis of muscles that move the eyeball in the direction we want, optic nerve head swelling and susceptibility to various eye infections.
What is diabetic retinopathy?
Characteristic changes in the retina caused by diabetes are together known as Diabetic Retinopathy. It is the most common eye disease due to diabetes and the most common cause of loss of vision in diabetics.
Some of the earliest damage is seen in very small blood vessels (capillaries) which become weak, the bulge at places and leak blood and fluid into the retina. These outpouching or bulges are seen as tiny red dots called microaneurysms. The leakage from these damaged capillaries and microaneurysms causes spots of blood in the retina, yellow deposits of fats and swelling of retina. In addition, there can be white spots in retina due to blockage of flow in the nerve fibers of the retina and dilatation and beading of the retinal veins. If all or any of the above changes are seen then we call this as Nonproliferative Diabetic Retinopathy or Background Diabetic Retinopathy (figure 3). This is further classified as mild, moderate or severe depending upon the severity of the changes seen.
Shows various findings in the retina in a moderate non-proliferative diabetic retinopathy and maculopathy
If the diabetic retinopathy progresses from this stage then small blood vessels (arterioles) may become closed due to thickening of their walls and clot formation. This leads to less supply of oxygen to the retina, triggering the distressed cells to produce a special protein that stimulates the formation of new blood vessels, aptly called as Vascular Endothelial Growth Factor (VEGF). This protein VEGF- stimulates the formation of abnormal new blood vessels on the surface of retina. When new blood vessels appear on the surface of the retina we call it as Proliferative Diabetic Retinopathy (figure 4). The VEGF also alters the permeability of the capillaries leading to leakage of fat and fluid in the retina. This causes swelling of the macula if blood vessels near the macula are affected.
These abnormal new blood vessels are fragile and may rupture and cause sudden bleeding covering the retina(sub-hyaloid hemorrhage) or in the cavity of the eye clouding the vision
If the growth of these abnormal blood vessels is exuberant and if untreated, they may later form scar tissue on the surface of the retina which may contract and lift the retina (tractional retinal detachment) from its normal position. This is called as tractional retinal detachment (Fig.6). If the tractional retinal detachment affects the center of the eye -macula, then the vision may be severely affected. In patients who are not treated in time or in whom the disease progresses relentlessly total blindness may be the end result.
What is diabetic macular edema?
The central part of the retina is called macula and is the most important area enabling us to see clearly. When very small vessels near the macula leak fluid it may lead to a collection of fluid in the macula leading to its thickening or swelling. This is called diabetic macular edema. There may also be lipid deposits in the macula-hard exudates.
This swelling reduces vision and causes blurring of images. Diabetic macular edema can be present in both nonproliferative diabetic retinopathy and proliferative diabetic retinopathy. It is the most common cause of impairment of vision in diabetic patients and needs treatment.
A recently available new instrument, optical coherence tomography scan, shows the amount of thickness in the center of the macula very clearly. Fig.7 (normal retina) Fig.8 diabetic macular edema.
Who gets diabetic retinopathy?
Diabetic retinopathy usually develops in diabetics with
• long duration of diabetes
• poorly controlled diabetes
• presence of high blood pressure
• presence of high cholesterol
• obesity and
• pregnancy
• puberty
However many times diabetic retinopathy may be present in newly diagnosed diabetic patients. This is because detection of type II diabetes is usually late as there may not be any symptoms of diabetes in the initial few years.
How common is diabetic retinopathy?
As the duration of diabetes in a patient increases the chances of diabetic retinopathy also increase. In patients suffering from type II diabetes for 20 years -nearly 80% will have some diabetic retinopathy.
In patients suffering from Type I diabetics for 15 years – nearly 100% of patients will have some diabetic retinopathy.
The severe form of the disease called proliferative diabetic retinopathy develops in up to 15% of type II diabetics of 20 years duration and nearly 60% of type I diabetics of 20 years duration.
Diabetic maculopathy is swelling of the center of the retina (called macula) and commonly affects vision. This condition is seen in 30% of type I and type II patients with diabetes of 20 years duration.
How do I know that I have diabetic retinopathy?
You may have good vision even when your retina may be affected by diabetic retinopathy. Hence regular examination of the retina is needed for all the diabetic patients.
When the diabetic retinopathy causes macular edema, vitreous hemorrhage or tractional retinal detachment, then the patient may experience blurred vision or diminished vision, seeing cobwebs or sudden loss of vision. It is always advised to have regular eye examinations before the symptoms appear.
When should I get my eyes checked if I have diabetes?
For type I diabetics (diabetes starts at a very early age and they need to take insulin regularly) who are usually children, the eye examination is done 3-5 years after the diagnosis of diabetes. After that first examination, subsequent follow-ups are a must. Annual follow-ups are advised if the retina is not affected. More frequent follow-ups are advised if there is diabetic retinopathy depending on its severity.
For Type II diabetics (diabetes starts relatively late, usually in the 30s) it is must have eye examination soon after diabetes is detected because nearly 10% of newly diagnosed diabetics may have some diabetic retinopathy. Some of them may even be having vision-threatening diabetic retinopathy. Subsequent follow-ups are decided by the presence and severity of the diabetic retinopathy.
How does the eye doctor examine my eyes for diabetic retinopathy?
The eye doctor records your vision and examines the front part of the eye. Then the pupils are dilated with drops and the retina is examined with special instruments and lenses. It is a painless procedure and it takes about one hour for the total eye examination.
What is the treatment given for diabetic retinopathy?
It is important to control blood sugar and blood pressure effectively as their control may halt the progress of diabetic retinopathy and improve the vision. However many patients need treatment for diabetic retinopathy depending upon its severity. Treatment is indicated when there is
a) diabetic macular edema b) proliferative diabetic retinopathy or c) tractional retinal detachment that affects the macula
a) Diabetic macular edema
As diabetic macular edema affects the vision it needs treatment in most cases. It is very important to realize that the treatment of diabetic macular edema may be needed for a long time as it may keep recurring in some patients.
i) Laser treatment–is used to seal the leaking capillaries or microanuerysms or area of edema if the swelling is away from the center of the macula. It is an outpatient procedure and does not cause pain.
ii) Injection of special drugs into the vitreous cavity of the eyeball is advised when the swelling involves the center of the macula. The special drugs include –Bevacizumab, ranibizumab, aflibercept and dexamethasone implant.
As mentioned earlier VEGF increases the leakage from very small blood vessels(capillaries) leading to edema. Bevacizumab, ranibizumab and aflibercept act by inhibiting VEGF and prevent leakage from the capillaries. Hence they are called anti-VEGF drugs. We can use any one of the drugs. However, the injections need to be given monthly for at least 3 months initially and later as and when required. A regular follow up is needed.
iii) Dexamethasone implant(OZURDEX) is a special device containing slow releasing steroid drug that reduces inflammation and leakage from capillaries. The advantage of this drug is its effect lasts for three months.
b) Proliferative diabetic retinopathy
When new vessels develop on the surface of the retina the risks of bleeding increase and hence treatment is must in these cases of proliferative diabetic retinopathy. The regular check-ups can detect the new blood vessels before they have caused bleeding.
i) Application of laser burns covering most of the retina except the center. The treatment can be carried out in 2-4 sittings. Usually, no anesthesia is needed except local anesthetic drops prior to laser. This treatment is called pan-retinal photocoagulation (PRPC). The laser causes the new blood vessels to close and stop bleeding.
ii) Injection of Anti VEGF drugs is also being used instead of a laser, but monthly injections for 7-10 times have to be given to get desired results.
iii) If the proliferative diabetic retinopathy has already caused vitreous hemorrhage causing sudden loss of vision, then, a laser may not be possible initially. A waiting period of 4-8 weeks may be appropriate for the blood to be cleared by the body and later laser treatment can be done. However, if the blood does not get cleared when such eyes need surgical treatment.
c) Tractional Retinal detachment
When the proliferative diabetic retinopathy progresses aggressively the retina may be lifted up causing tractional retinal detachment. If it is near the macula or involves the macula then surgery is advised to remove the membranes from the surface of the retina and flatten it.
d) Surgery for advanced stages of diabetic retinopathy
As mentioned earlier surgical treatment is advised when there is dense vitreous bleeding that is not clearing even after 4-8 weeks of waiting. It is also advised when there is tractional retinal detachment that is close to macula or it is very near to the macula. We also advise surgery when there are membranes of the surface of the macula that has reduced the vision. The surgery is a complex one and needs specialized instrumentation.
SUMMARY
Diabetic retinopathy is an important complication of diabetes and can cause severe visual problems. Control of blood sugar and hypertension may slow the development and progression of diabetic retinopathy. It is important to have regular eye check-ups with a dilated retinal examination. Effective treatment options like a laser, intravitreal injections of special drugs and surgical treatment has done promptly can preserve the vision. Regular checks up are very important.
About the Author:
Dr.Vivek B Wani., MS FRCSEd Consultant Ophthalmologist (Vitreoretina)
KLES DR. PRABHAKAR KORE HOSPITAL AND MRC-NEHRU NAGAR, BELAGAVI
M: 9449563506
