Diabetes mellitus is one of the leading causes of irreversible blindness worldwide. In the United States, it is the most common cause of blindness in people younger than 65 years. Severe diabetic eye disease most commonly develops in people who have had diabetes mellitus for many years. High blood sugar and other abnormalities in metabolism found in people with diabetes mellitus can damage the blood vessels in the body. This damage to the blood vessels leads to poor circulation of blood to various parts of the body. Some of the most sensitive tissues to decreased blood flow and oxygen delivery include the feet, heart, kidneys, and eyes. The primary part of the eye affected by diabetes mellitus is the retina.
The better control diabetics have of their blood sugar, the fewer problems they will have in the long run. The most important method of preventing eye disease related to diabetes is to maintain strict control of blood sugar. High blood pressure and high lipid or cholesterol levels must also be treated as these conditions exacerbate the retinal disease caused by diabetes. In mild cases of diabetic eye disease, vision may be stable for many years. Eye surgery can also improve vision in many cases.
There are two major stages of diabetic retinopathy. The earlier stage of diabetic retinopathy is called non-proliferative diabetic retinopathy. The later, more advanced stage of diabetic retinopathy is called proliferative diabetic retinopathy.
Non-proliferative diabetic retinopathy
Elevated blood sugar levels cause damage to the walls of small blood vessels in the retina. These small blood vessels may begin to “break down” as damage accumulates with time. This leads to the accumulation of fluid (edema), protein deposits (hard exudates) and blood (hemorrhages) inside the retina. Diseased blood vessels will also develop thin walled pouches called microaneurysms, which are one of the earliest signs of diabetic eye disease.
This process of blood vessel damage and leakage in the retina is called background diabetic retinopathy or non-proliferative diabetic retinopathy. If fluid accumulates in the central part of the retina (called the macula), this leads to a condition called diabetic macular edema. In severe cases of blood vessel damage, the small capillaries that supply the center of the vision (macula) may close permanently. This condition is called macular ischemia.
Macular edema and macular ischemia are common causes of visual loss in diabetics. Central visual blur, visual distortion, and/or a blind spot are common symptoms in patients who have moderate to severe macular disease from non-proliferative diabetic retinopathy.
Many patients with non-proliferative diabetic retinopathy have the early stages of the disease and do not require treatment. However, scheduled retinal examinations by an eye doctor are always necessary for patients with diabetic retinopathy.
Proliferative diabetic retinopathy
Damage to the blood vessels caused by high blood sugar eventually leads to decreased blood flow and lower amounts of oxygen delivered to the retina. As a response to poor oxygen delivery to the retina, the body may create new blood vessels which grow on the retina’s surface. The process of new blood vessel formation is called retinal neovascularization.
Retinal neovascularization is the hallmark of proliferative diabetic retinopathy. While new blood vessels may sound like a good thing, they are actually more harmful than beneficial. The new blood vessels are extremely fragile and unstable. If left untreated, neovascularization can lead to bleeding and scar tissue formation inside the eye. This often results in severe vision loss. In advanced stages of the disease, this vision loss may be permanent. Early detection and treatment is important to prevent vision loss from proliferative diabetic retinopathy.
In severe cases, neovascularization can develop in the front of the eye on the iris (the colored part of the eye). If abnormal vessels develop on the iris, they can block the filter which drains fluid from the eye, causing the pressure inside the eye to increase dramatically. This condition is called neovascular glaucoma and can lead to eye pain and further vision loss.
Medical treatment of diabetic eye disease is generally directed at the underlying problem – the diabetes itself. The better control diabetics have of their blood sugar, the fewer problems patients will have in the long run. The most important method of preventing eye disease related to diabetes is to maintain strict control of blood sugar. High blood pressure and high lipid or cholesterol levels must also be treated as these conditions exacerbate the retinopathy caused by diabetes.
Treatment of diabetic retinopathy may also include injection of medicines into the eye. These are called intravitreal injections. Recent studies have shown that certain drugs injected into the eye can reduce swelling of the retina and reverse retinal neovascularization. Even though injections can be very helpful, usually additional treatments are necessary to achieve the best long term results.
Non-proliferative diabetic retinopathy can also be treated with laser when swelling of the central retina develops. Swelling of the central retina occurs when diseased blood vessels in the retina begin to leak fluid or lipids. Fluid begins to accumulate in the retina causing thickening and distortion of the retinal layers. This results in blurred or distorted vision. This condition is called diabetic macular edema. Diabetic macular edema is treated with a laser technique called macular photocoagulation. This laser treatment is performed in the office and involves focusing a beam of laser light to treat leaking blood vessels and areas of retinal swelling. Macular photocoagulation has been proven to reduce the risk of vision loss due to macula edema.
Proliferative diabetic retinopathy is treated with both laser and operating room surgery. Pan-retinal photocoagulation (PRP) is the laser technique performed to treat neovascularization of the retina. During this treatment the majority of the peripheral retina is treated with laser spots to promote regression of neovascular tissue. Pan-retinal photocoagulation has been proven to reduce the risk of vision loss due to proliferative diabetic retinopathy.
If extensive new blood vessel growth, scar tissue formation, or bleeding inside the eye has already occurred, a surgical procedure known as a vitrectomy may be recommended. This surgery is performed in an operating room at a hospital or ambulatory surgery center. The vitreous (a gel-like fluid) and the blood inside the eye are removed and replaced with a clear fluid. Scar tissue is also removed from the retinal surface during a vitrectomy when necessary. A vitrectomy surgery is often combined with laser treatment and/or retinal detachment surgery.
The earlier diabetic eye disease is diagnosed and treated (if necessary), the better the prognosis. For those with diabetic retinopathy, the prognosis is determined by the severity of the disease. In mild cases and in those treated early, vision may be stable for many years and eye surgery can improve vision in many cases. In severe cases, relentless and progressive irreversible vision loss may occur despite the best treatment. If you have diabetes mellitus, “an ounce of prevention is worth a pound of cure.” Following the advice of your medical doctor in regards to proper diet and exercise, blood sugar monitoring, and taking diabetic medication, the chances of developing serious problems from diabetes decrease dramatically.