Nine out of ten people with diabetes eventually develop a complication that affects the eyes known as diabetic retinopathy. This complication affects the blood vessels inside the eye and can lead to blindness if untreated. However, if diagnosed and treated early much of this blindness can be preventable.
STRUCTURE AND FUNCTION OF THE EYE
The eye is similar to a camera. It has a clear lens focusing light to a light sensitive membrane (the retina) which creates nerve signals. These signals form the basis of vision and are sent to the brain via the optic nerves. The brain processes the signals and eyesight is perceived by the individual.
The retina is a thin transparent membrane spread over the inside of the back of the eye. It contains specialized cells called rods and cones and it is these cells that register the light. The cone cells are responsible for clear, straight ahead viewing and color vision. The rod cells provide night and side vision. The retina is kept alive by blood vessels both within its structure and underneath it. The blood vessels are known as retinal arteries, capillaries and veins. Clearly anything that interferes with the function of the retina will have some impact on eyesight.
The most important part of the retina is where the cone cells are and this is called the macula. It represents the center of vision.
DEFINITION AND CLASSIFICATION OF DIABETIC RETINOPATHY
Diabetic retinopathy (also referred to as DR) occurs when tiny blood vessels in the retina become damaged. When it starts, most people do not notice any changes in their vision. However, if left untreated this diabetes complication can result in permanent blindness.
There are two stages of retinopathy-Nonproliferativeand Proliferative
NonProliferative is the earlier of the two changes and is more common.In this stage there may be bleeding inside the retina (haemorrhages); Leakage of serum into the retina causing a “wet retina” or protein deposits in the retina (exudates).One of the consequences of this change is that the retina does not receive enough oxygen which can cause a progression to the next stage. This early stage usually produces no visual symptoms but if there is fluid in the central portion of the eye then vision may drop. (macular edema)
Proliferative is the next stage. New abnormal vessels can develop in the retina and grow towards the center of the eye. These vessels frequently bleed into the clear jelly in the center of the eye (vitreous haemorrhage). Such bleeding episodes usually cause severe visual difficulties in patients. Small bleeds may clear up on their own but larger bleeds may need surgery. These abnormal vessels may also produce large scars in the retina that may cause the underlying retina to detach producing a retinal detachment.
RISK FACTORS FOR DIABETIC RETINOPATHY
The longer a person has had diabetes the greater the risk of diabetic retinopathy. About 80% of people who have diabetes for more than 15 years will likely eventually develop retinopathy. However, about 13% of newly diagnosed adults will have retinopathy at the time of diagnosis.
The consistency of good control of sugar during diabetes also impacts on the development and severity of diabetic retinopathy.
High blood pressure, kidney failure and cholesterol can adversely affect the severity of diabetic retinopathy.
Pregnancy can sometimes result in a rapid acceleration of diabetic retinopathy.
For all these reasons, a newly diagnosed adult should have a full eye examination at the time of diagnosis and then one to two yearly thereafter. A child who develops diabetes need not be examined at diagnosis but should have an eye examination after 5 years of disease. An insulin dependent female planning pregnancy should have an eye examination at three months into
Smoking does accelerate the damage diabetes does to the retina. A person with diabetic retinopathy should not smoke. Nor should anyone else.
DIAGNOSIS OF DIABETIC RETINOPATHY SYMPTOMS
Blurring of vision is the main symptom associated with diabetic retinopathy but this usually occurs when the disease is already well established. Many people with diabetic retinopathy will have no symptoms at all. Diabetic retinopathy does not cause pain. People with proliferative retinopathy may experience floating spots in their vision due to bleeding within the eye.
A eye doctor will go over your full medical history including all other health problems, medications, allergies. Your vision will be measured.
Your eye doctor will examine your eyes and should use drops to dilate or open the pupils. The doctor will be able to examine the retina in detail. A photo of a normal retina is seen below. If the retina is diseased then the doctor may carry out a test known as fluorescein angiography. This is a photographic record of the state of the retinal blood vessels. A yellow dye is injected into an arm vein and photographs using a special camera are taken. A normal photograph from a fluorescein angiogram is depicted below.
The eye examination and tests will enable the eye doctor to determine the extent and severity of the diabetic retinopathy. Treatment and recommendations will be made based on your diagnosis.
In early non-proliferative diabetic retinopathy, most people usually have no symptoms and there are small areas of leakage in the retina.
If diabetic macular edema occurs, then laser treatment may be required.
More established non-proliferative retinopathy may require careful monitoring or laser treatment.
In proliferative diabetic retinopathy, much of the retina is affected by obstruction of retinal capillaries. This may not necessarily affect vision directly but it does cause “new” capillaries to grow on the surface of the retina or optic nerve.
These new vessels are prone to bleeding and can fill the eye with blood, dramatically blurring vision. In addition, scar tissue can develop causing retinal detachment to occur.
TREATMENT OF DIABETIC RETINOPATHY
Improvement of diabetic control, reduction of risk factors such as high blood pressure and cholesterol and regular eye examinations will all help toward reducing the impact of diabetic retinopathy on a person’s eyesight.
The two treatments for diabetic retinopathy, once established, are:
2. vitrectomy surgery
Neither of these treatments cures retinopathy. The best that can be achieved usually is slowing or preventing further vision loss.
LASER TREATMENT FOR DIABETIC RETINOPATHY
Laser treatment is usually indicated to control leakage from capillaries in diabetic macular edema, or to shrink “new” vessels in proliferative diabetic retinopathy. In diabetic macular edema, small applications of laser are used to “cauterize” the leaking vessels using thermal energy. In proliferative retinopathy, more intensive treatments to much of the retina are required to shrink the new vessels.
Laser treatment may be associated with discomfort or pain. Some treatments may require pain relieving medication or anesthetic injections to numb the eye. Eyesight may fluctuate during a
course of treatment.
SURGERY FOR RETINOPATHY
Vitrectomy surgery is required for advanced cases of proliferative diabetic retinopathy. When there has been severe bleeding into the eye which has not resolved spontaneously, then the blood (contained with the normal vitreous gel) is removed using fine instruments. The instruments are passed through small cuts in the white part of the eye. If the retina is detached then scar tissue is cut and peeled away from the retina. The vitreous gel does not regrow and your eye does not require the gel for vision. Typically the gel is replaced at the time of surgery with fluid, gas or liquid silicone. Laser and cryotherapy may be used during surgery. Cataract surgery may be required at the time of vitrectomy surgery. Surgery can take one to four hours depending on complexity. Following surgery there will be a gradual improvement in vision over the coming weeks to months. You will need to use eye drops for 4-6 weeks after surgery.
COMPLICATIONS OF LASER TREATMENT
- Discomfort and pain
- Fluctuating vision
- Some loss of side and night vision
- Some loss of color vision
- Slight risk of inadvertent damage to the macula which could reduce central vision
COMPLICATIONS OF SURGICAL TREATMENT
- The retina itself may become damaged during the procedure necessitating further surgery
- Further bleeding into the eye after surgery
- Reduction in overall quality of vision
- Complications associated with anesthesia.
You should discuss the risk of complications with your eye doctor.