Diabetic retinopathy is the most serious complication of diabetes. Diabetes affects all body systems, and the eyes are no exception.
Diabetes affects the eyes in several potentially devastating ways. It can destroy optic nerve fibers, causing optic atrophy; increase the likihood of cataracts and glaucoma; and affect the eye muscles, iris, and lens of the eye. However, it is the retina that is the most commonly affected portion of the eye.
Retinopathy is the medical term for damage to the many capillaries (tiny blood vessels) that nourish the retina. These blood vessels are often affected by the high blood sugar levels associated with the disease. The longer a person has the disease, the greater the likelihood of developing diabetic retinopathy.
Initially, only mild vision problems are experienced; but, as the condition worsens, vision is threatened. With early detection and treatment, the risk of severe vision loss is less than five percent – provided that blood sugar and blood pressure are kept under the best control.
When diabetes is present, the body does not produce or utilize glucose properly. Although sugar in the blood is vital to health because it is the main source of energy for body cells, too much can cause a host of problems. It can damage the capillaries that supply nutrients to such organs and tissues as in the brain, nerves, kidneys, and the eyes.
Damage to the retina from high blood sugar occurs when microaneurysms form on the walls of the small blood vessels, causing the vessel walls to become porous, leaking fluid into the retina.
Extensive leakage can leave deposits of fatty material, called exudates, in the retina. When swelling occurs in the macula, vision may be reduced or blurred. As blood vessel walls weaken, the blood vessels may close off, reducing blood flow and depriving the retina of oxygen. This can trigger proliferative diabetic retinopathy when the oxygen-starved retina grows new blood vessels.
Unfortunately, these new blood vessels do not resupply the retina with a normal blood flow. Instead, they may produce such complications as vitreous hemorrhage, traction retinal detachment, or neovascular glaucoma.
Vitreous hemorrhage: The new blood vessels may bleed (hemorrhage) into the vitreous. If the amount of bleeding is small, a few dark spots or floaters may be seen. In more severe cases, blood can completely fill the vitreous cavity and block all vision. Vitreous hemorrhage by itself does not cause permanent vision loss. The blood eventually clears from the eye, usually within a few months, and vision returns to normal unless the retina is damaged.
Traction retinal detachment: The new blood vessels are often accompanied by the growth of scar tissue which eventually shrinks. But, as it shrinks, it pulls the retina away from the back wall of the eye, causing blank and blurred areas in the vision field.
Neovascular glaucoma: The proliferation of blood vessels on the retina may be accompanied by the growth of abnormal new blood vessel on the iris. This can interfere with the normal flow of fluid out of the eye and cause pressure in the eye to build up. The result is neovascular glaucoma, a serious complication of diabetic retinopathy that can cause pain, vision loss, and the loss of the eye, if not treated successfully. Untreated neovascularization and proliferative diabetic retinopathy often lead to such severe visual loss that the big “E” cannot be seen on the Snellen chart from ten feet away.
There are two basic types of diabetic retinopathy: proliferative and nonproliferative. Usually both eyes are affected, although the disease may be more advanced in one eye than in the other.
Nonproliferative diabetic retinopathy (NPDR) is also called “background diabetic retinopathy.” It is an early stage of the disease and the most common type of retinopathy where the symptoms are often mild. NPDR occurs when the walls of blood vessels in the retina weaken. Tiny bulges called microaneurysms protrude from the vessel walls. This is known as “outpouching”.
These bulges begin to leak, oozing fluid and blood into the macula, the central part of the retina. This fluid collection is called macular edema which will affect reading and other tasks. As the condition worsens, it becomes known as proliferative retinopathy. As NPDR progresses, other signs of damage appear, including patches of swollen nerve fibers, often called “cotton wool spots” – so named because they look like fluffy wisps of cotton.
Although mild NPDR may not affect the ability to see clearly, vision problems from the more severe form are usually the result of swelling of the macula or the closing of capillaries, reducing blood flow to the macula. This is known as “macular ischemia”. When the macula does not function properly, central vision decreases; but the peripheral vision usually remains normal. Treatment involves close monitoring by an eye doctor.
Surgical intervention may be necessary and includes two types: photocoagulation and vitrectomy.
The goal of photocoagulation is to stop blood and fluid leakage in the retina. A high energy laser beam is used to create small burns in the areas of the retina, with abnormal blood vessels to seal any leaks. This is done as outpatient surgery.
Vitrectomy involves the use of delicate surgical instruments to remove the blood-filled vitreous. A vitreous cutter cuts the tissue and removes the pieces from the eye, bit by bit. An infusion cannula or tube replaces the volume of removed tissue with a balanced salt solution to maintain the normal shape and pressure of the eye. A vitrectomy is also used to remove scar tissue when it begins to pull the retina away from the wall of the eye. This allows a detached retina to settle back and flatten out. During a vitrectomy, the surgeon may also perform panretinal photocoagulation with a laser probe. This can prevent renewed growth of abnormal blood vessels and bleeding.
Proliferative diabetic retinopathy (PDR) is the more advanced form of the disease. About half the people with very severe NPDR progress to PDR within a year. Retinopathy becomes proliferative when abnormal new blood vessels grow (proliferate) on the retina or the optic nerve. The blood vessels can also grow into the vitreous. This abnormal growth follows the widespread closing of capillaries in the retina because of high blood sugar levels.
The condition can cause vision loss of both the central and peripherial vision fields. The new blood vessels may leak blood into the vitreous, which clouds or even blocks the vision. This prevents light from passing through the eye to the retina, causing diminished vision. The new vessels can also cause scar tissue to develop, which can make the retina pull away from the back of the eye (retinal detachment) and can lead to blindness if not treated.
Blurred vision in diabetics is commonly brought on by fluctuations in blood sugar and is a strong indicator that the blood sugar level may be too high. Prolonged periods of excessive blood sugar cause sugar and its breakdown products to accumulate in the lens. This accumulation sucks up water and makes the lens swell, resulting in nearsightedness, which may subside when the blood sugar is brought under steady control.
Blurred vision can also be caused by macular edema or swelling, regardless of blood sugar levels. This is cause for greater concern because macular edema often develops in people with diabetic retinopathy. The swelling may fluctuate during the day, making vision become better or worse. If blood vessels in the eye are hemorrhaging, spots or floaters may be seen temporarily. These small spots are often followed within a few days or weeks by larger spots or clouds, which are caused by more massive hemorrhaging.
Other complications include detachment of the retina because of scar tissue formation and a form of glaucoma associated with the growth of abnormal blood vessels on the iris.
For PDR, a form of laser surgery called panretinal or scatter photocoagulation is used. With this technique, the entire retina, except the macula, is treated with randomly placed laser burns. This treatment causes the abnormal new blood vessels to shrink and disappear, reducing the possibility of vitreous hemorrhage. Panretinal photocoagulation is usually done in two or more sessions and significantly reduces the risk of severe vision loss. This procedure is actually a trade-off. Some of the peripheral vision is sacrificed in order to save as much of the central vision as possible.
Signs and symptoms of diabetic retinopathy usually include no visual symptoms or pain. The disease may even progress to advanced stages without any noticeable change in vision. Noticeable symptoms include the following:
- “spiders” or “cobwebs” or tiny flecks floating in the vision field
- dark streaks or a red film that blocks vision
- vision loss, usually in both eyes, but more so in one than the other
- blurred vision that may fluctuate
- a dark or empty spot in the center of the vision field
- poor night vision
- difficulty adjusting from bright light to dim light
The main risk factor for developing retinopathy, or eye problems, is diabetes, either type I or type II. Since the risk increases the longer one has the disease, those with type I diabetes are at an especially high level of risk because their diabetes develops at an earlier age. When insulin is taken, the risk increases.
Other risk factors stem indirectly from diabetes as those with the disease often have other problems including the following:
- poorly controlled blood sugar levels
- kidney disease (nephropathy)
- nerve damage (neuropathy)
- high blood pressure
- high blood fats (elevated levels of low density lipoprotein (LDL) cholesterol and triglycerides)
- pregnancy. Women with type I diabetes who become pregnant have about a 10% chance of developing NPDR. Women who already have NPDR when they become pregnant tend to experience a progression of the disease, although it may improve after delivery. The most common eye birth defect associated with maternal diabetes is “optic nerve hypoplasia.” The optic nerve connects the eye to the brain and provides the conduit by which light signals from the retina are conveyed to the brain for perception. Fortunately, many children with optic nerve hypoplasia, do not have significant vision loss.
The absence of an effective medication in Western medicine leads many patients with retinopathy to consider alternatives. Although alternative medicines are helpful in prevention of retinopathy, there is still no substitute for having a good control of blood sugar through diet and exercise.
In traditional Chinese medicine, diabetes mellitus is thought to occur through an imbalance of the yin and yang, and the disorder of Zang-Fu (viscera). Diabetes mellitus develops because of excess “pulmonic heat,” “stomach heat,” and kidney insufficiency. Excessive heat of the lung and stomach then consumes the body fluid and results in deficiency of “yin”. The principal treatment, therefore, is reducing heat, nourishing the “yin” and strengthening the kidney.
Common prescriptions are composed of such herbs as Radix trichosanthis, Rhizoma polygonati odorati, Radix scrophulariae, raw Radix glehniae. Flos buddlejae and Semen celosiae may be helpful in patients with retinopathy.
In Ayurvedic medicine, the extract Gymnema sylvestre is widely used. Its active ingredient is “gymnemic acid” which prevents the taste buds from being activated by sugar molecules and keeps the intestine from absorbing sugar molecules. The herb allegedly works by reducing the appetite for sweet-tasting food and by reducing the metabolic effects of sugar by lessening its absorption in the intestines.