Diabetes is a disease that affects the ability of the body to produce or respond to insulin. This hormone causes blood glucose (blood sugar) to enter the cells of the body for energy. Diabetes is the fifth-deadliest disease in the United States, and it has no cure.
Diabetic retinopathy, which damages the small blood vessels of the retina, is the leading cause of blindness among patients younger than 65. Approximately fourteen million people in the United States have diabetes mellitus. Of these half are unaware that they have the condition. The most common type of diabetes is non-insulin-dependent diabetes mellitus (NIDDM) whereby control of blood sugar is with oral medications or diet. This form of the disease has been called “adult-onset” or Type II diabetes. The other more severe type of diabetes is called insulin-dependent diabetes mellitus (IDDM); insulin injections are used to regulate blood sugar levels. In younger patients this is synonymous with juvenile-onset or Type I diabetes. Patients with IDDM are at greater risk for diabetic retinopathy.
The risk of diabetic retinopathy, which causes leakage of the small blood vessels, increases with duration and control of blood sugar levels. After 5 years, approximately one-quarter of patients with IDDM will demonstrate damage to the retinal blood vessels. By 15 years, almost everyone with IDDM will have some retinal involvement. Diabetics have 25 times the usual risk of blindness. Glaucoma, cataract, and corneal disease are more common in people with diabetes and contribute to the high rate of blindness. In addition, high blood pressure or pregnancy increases the risk of retinopathy in diabetics. These statistics demonstrate the risk for diabetic patients; the need for regular eye check-ups and treatment,which will reduce the risk of blindness.
Diabetic retinopathy is a term used to describe the changes in the blood vessels of the retina. There are two types of retinopathy-Background and Proliferate Diabetic Retinopathy. Background or non-proliferative is much, more common. There may be bleeding within the layers of the retina (hemorrhages); leakage of serum into the retina causing protein deposits in the retina called exudates. If there is fluid in the macula of the eye then vision drops (macular edema). If the process becomes severe enough, the retina does not receive enough oxygen. New abnormal vessels (neo-vascularization) develop in the retina in response to the lack of oxygen. These new vessels, which develop during the Proliferative Phase, are fragile and are prone to bleed. If they bleed into the jelly in the center of the eye, a vitreous hemorrhage develops. Often these bleeding episodes cause severe visual loss in patients. Smaller bleeding episodes may clear up on their own but larger, repeated or bleeding lasting more than 6 mos. may need surgery. These newly formed abnormal vessels may also produce fibrous bands in the retina that may contract and produce a retinal detachment. Fortunately, Proliferative diabetic retinopathy especially with vitreous bleeding is much less common.
Diabetes earliest sign may be an abrupt change in your eye glass prescription. The blood sugar effects with water content of the lens of the eye and, therefore, your eyeglass prescription. Sudden increases in blood sugar will cause an increase in myopia. This often occurs before the detection of the disease. Diabetic retinopathy may begin in your eyes without you noticing any change in vision. Unfortunately, there may be extensive and severe changes before your vision is affected. Thus, it is very important to have your eyes examined regularly at six-month or yearly intervals depending on duration and/or severity of your diabetes.
A dilated retinal examination or Optos examination is performed. Dilatation, is like opening the door of closet, so that we can see what is inside to properly evaluate the retina. We look for evidence of diabetic retinopathy. Based on this examination a Fluorescein Angiogram may be advised.
Fluorescein angiography is a dye test often used to assess the damage to the retina and it’s blood vessels from diabetes. A dye is injected into a vein of one arm. Pictures are taken of the retina as the dye passes through the vessels of the eye. Since there is a risk of allergic reactions, a history of allergic reactions is important. There may be mild nausea during the procedure. The skin and urine may turn yellow for 24 to 48 hours. These angiograms show areas of leakage, areas of oxygen-starved retinas, and weak, fragile new vessels. Based on the results a LASER may be advised.
Laser stands for Light Amplification by Stimulated Emission of Radiation. The Laser produces a concentrated beam of light that burns small areas of the retina.
Laser surgery is usually an outpatient procedure. First, an anesthetic drop is instilled in the eye. A contact lens is put on the eye which directs the laser light to the retina. The treatment is usually painless. It can take up to 60 minutes to complete the treatment.
The most important treatment for diabetes and its complications including diabetic retinopathy is control of the diabetes. Tight control of both blood sugar, weight and blood pressure control are important in preventing the ocular complications of diabetes and slowing the progression of the disease.
In addition diabetics should keep a tight control on their blood chemistry. The following are the recommended values:
Once retinopathy occurs, laser therapy is the current modality of treatment. Lasers have been used since the 1970s. Laser treatment is an office outpatient procedure. Most patients tolerate the procedure extremely well with little discomfort. Laser surgery is used to treat both diabetic macular edema and proliferative diabetic retinopathy.
Laser treatment for diabetic macular edema stabilizes vision by stopping blood vessels from leaking fluid into the retina. Either focal treatment for small discreet areas of leakage or a grid pattern is used when the leakage is diffuse in nature. After treatment, the patient may notice small spots of decreased visual sensitivity. Usually these spots become less noticeable with time. It is possible that the vision may get a little worse after laser. However, the laser helps prevent further reduction in vision. Studies have shown that most patients who receive laser for macular edema will have better vision in the future than if they hadn’t received the treatment.
Laser photocoagulation has been shown to reduce the risk of both moderate and severe permanent vision loss by 50-75%. Laser therapy is destructive by design; some retinal tissue is intentionally destroyed in order to preserve the function of other, more visually important areas of retina. As a result, patients often experience a loss of peripheral vision, abnormal blind spots , and reduced ability to see at night . Pan-retinal laser photocoagulation for treatment proliferative diabetic retinopathy results in a loss of vision in approximtately 11% of treated patients. Sometimes laser treatment doesn’t stop the progression of retinopathy and/or vision loss.
In the less common proliferative diabetic retinopathy (PDR) new blood vessels grow onto the retina in response to need of nourishment and oxygen which is deprived by the diabetic process. Unfortunately these new blood vessels are weak and fragile. They bleed easily and may contract pulling on the retina causing a retinal detachment. These abnormal neo-vascular vessels (new blood vessels) found in proliferative diabetic retinopathy are treated with pan retinal (scatter) laser photocoagulation or PRP. Laser treatment is given to the peripheral retina which is not receiving an adequate blood supply. It is believed that by treating the areas of retina deprived of normal vasculature, the reduction in demand for nutrients and oxygen by damaging retina will halt the development of new blood vessels. It is important to recognize that this laser procedure, is destructive and does not improve vision. It is intended to prevent the blinding complications of diabetic retinopathy. There is some loss of side (peripheral) and color vision is following this treatment . Pan retinal photocoagulation has been shown to reduce the risk of severe visual loss associated with proliferative diabetic retinopathy.
Laser therapy can only stop the progression of the retinopathy. It cannot reverse the damage already done.
Recently drugs known as vascular endothelial growth factor (VEGF) have been used to block the signal causing growth of abnormal retinal blood vessels which occurs in proliferative diabetic retinopathy (PDR), venous occlusion, wet age related macular degeneration and ocular histoplasmosis. The three most common VEGFs are pegaptanib (Macugen
TM), ranibizumab (Lucentis
TM), and bevacizumab (AvastinTM) . Macugen and Avastin have both been shown to improve visual acuity and reduce retinal thickening due to diabetic macular edema, whereas Avastin and Lucentis have been shown to cause regression of neovascularization due to PDR. Avastin is less costly than the other agents and is currently FDA-approved for treatment of colorectal cancer, but is being frequently used off-label.
Octreotide (SandostatinTM) is another drug that may prove beneficial in the treatment of proliferative retinopathy; it is currently used to treat certain endocrine tumors by suppressing blood vessel growth. Ruboxistaurin (ArxxantTM) is the first drug shown to prevent vision loss from macular edema in patients with moderate to severe non-proliferative diabetic retinopathy, it’s FDA approval remains in question.
A non-prescription, fat-soluble form of Vitamin B1 (thiamine) that has been shown to prevent diabetic retinopathy in laboratory animals and is currently in human trials. Genestein, a soy isoflavone that blocks VEGF receptors, has been shown to ameliorate retinal vascular permeability in diabetic animals and is currently available in an OTC eye supplement called Ocuvite DF.
While pan retinal photocoagulation is usually successful in halting the proliferative process, some patients progress despite laser treatment. Other patients may have bleeding into the vitreous of the eye. These eyes may require vitreous surgery. The main indications for vitrectomy are persistent vitreous hemorrhage and tractional retinal detachment. Vitrectomy surgery is a major eye operation. It involves removal of the vitreous from the eye. Frequently, the retina has to be reattached by surgically separating the scar tissue from the surface of the retina. Laser treatment is often applied at the time of vitrectomy. In some cases, a gas bubble is left in the eye following surgery to keep the retina flat against the back of the eye.
The glasses that the patient was using earlier can be continued. Often time special vision aids need to be prescribed. Magnifiers and other devices can help.