What Is Diabetic Retinopathy?
Diabetic retinopathy is the leading cause of blindness in the United States, yet about half of Americans with diabetes have never had a retinal examination, leaving them either are unaware of this serious complication or failing to take steps to prevent it.
Overview of Diabetes
To understand diabetic retinopathy, a quick refresher on diabetes is in order. The body’s endocrine system is responsible for regulating growth, sexual development, reproduction, and tissue functions such as cellular metabolism (energy use). Diabetes mellitus is a chronic endocrine disorder in which the pancreas produces no insulin or not enough insulin, the hormone that controls the amount of glucose (sugar) in the blood. Glucose is the body’s main source of fuel for cellular metabolism.
Type 1 diabetes generally develops during childhood and requires insulin for treatment, since the body produces little or none of its own. Type 2 diabetes usually develops in adulthood, although it’s becoming more prevalent among children. This form of diabetes is strongly associated with obesity and overweight (read Risk Factors for Diabetic Retinopathy). In this type of diabetes, the body either becomes resistant to the effects of insulin or does not produce enough of it. People with type 1 or type 2 diabetes can develop retinopathy, although it is more prevalent and tends to be more severe among people with type 1 disease.
Diabetic Retinopathy and Vision Loss
Because every cell in the body uses glucose for fuel, diabetes has a devastating effect on many organs and tissues if blood glucose is not carefully controlled. The circulatory system is no exception. It’s supplied with its own microcirculation—tiny blood vessels that nourish the retina and other structures of the eye. Damaged vessels can swell, leaking blood and other fluids.
Uncontrolled blood glucose diminishes vision by three mechanisms:
Macular edema. Fluid can leak into the macula, the central part of the retina that provides sharp central vision and allows us to see fine detail. This fluid accumulation causes the macula to swell, thickening it and elevating it from its normal position.
Macular edema can occur during any stage of diabetic retinopathy, but it is more likely to accompany proliferative retinopathy. In fact, about half of those with proliferative retinopathy also have macular edema.
Proliferation of blood vessels. Damaged blood vessels can’t adequately nourish the retina with oxygen and nutrients, so the retina begins to grow new vessels in an effort to meet its needs. These new vessels, however, are improperly formed and fragile. They can leak blood into the jelly-like vitreous humor inside the eyeball and into the retina itself (see How the Eye Works). These hemorrhages cause vision loss and permanent low vision.
Retinal detachment. The new vessels that form in the vitreous humor are often accompanied by scar tissue that can contract, tugging on the margins of the retina and forcing it to detach (see Causes of Blindness).
The longer you have diabetes, the more likely you are to develop signs of retinopathy. In addition, periods of poorly controlled glucose increase your risk of developing the disease earlier and of having more severe disease.
Generally, diabetic retinopathy is divided into nonproliferative (without new blood vessel formation) and proliferative (with new blood vessel formation) stages. Subcategories have been identified within these two broad stages.
In its early stages, nonproliferative retinopathy (also called simple or background retinopathy) usually does not diminish your vision and may cause no symptoms.
Mild nonproliferative. At this stage, the tiny vessels of the retina weaken, causing small, balloon-like outpouchings called microaneurysms.
Moderate nonproliferative. As red blood cells and proteins accumulate along the walls of the damaged vessels, blood flow through some of them becomes blocked. The vessels may rupture, creating blots or flame-like splinter hemorrhages (tiny areas of bleeding).
Severe nonproliferative. During this stage, microaneurysms and hemorrhages become widespread, occurring in all four anatomical quadrants (quarters) of the retina .
Lack of blood flow (because vessels are bleeding out into the vitreous rather than reaching the retina) starves the retina of oxygen and nutrients. As more and more vessels fail to deliver nourishment, abnormal new blood vessel growth begins. This process is called neovascularization.
The retina is a thin layer of tissue at the back of the eye. It’s sandwiched between the choroid (which lies beneath the sclera, the “white” of the eye) and the vitreous humor, a jelly-like substance that fills the cavity of the eyeball (see How the Eye Works). In someone with diabetic retinopathy, the vessels form on the vitreous side. These vessels can hemorrhage, diminishing vision by creating dark spots or flecks in your visual field. Sometimes the new vessels extend into the iris, leading to a particular type of glaucoma called neovascular glaucoma (see Glaucoma).
During the proliferative stage, hemorrhaging that causes inflammation may trigger the development of scar tissue. If this tissue contracts, it can pull at the edges of the retina, causing it to detach from the underlying vascular coat, the choroid. The retina can’t function when separated from its blood supply, and irreversible blindness will result (see Causes of Blindness)
Since symptoms during the early stages of diabetic retinopathy may be absent or subtle, everyone with diabetes should have a comprehensive dilated eye examination at least once a year (see Diagnosing Diabetic Retinopathy for specific screening recommendations). Of course, any flecks, spots, or blurs in your visual field should prompt an immediate visit to your vision care provider.
For more details on the specific symptoms read: Diabetic Retinopathy: Symptoms.
Risk Factors and Risk Reduction
The risk of developing diabetic retinopathy depends on many factors. As with all chronic disorders, some risk factors, such as the length of time you’ve had diabetes, lie completely outside your control. Others can be managed with lifestyle modifications and medical intervention. See Reducing Your Risk of Diabetic Retinopathy for a detailed discussion of risk factors.
Early signs of diabetic retinopathy include leaking blood vessels, swelling (edema), fatty deposits, and damaged nerve tissue. Your vision care specialist will use several tests to determine whether you have diabetic retinopathy and, if so, how to proceed based on the stage of the disease. See Diagnosing Diabetic Retinopathy for detailed information.
During the nonproliferative stage of diabetic retinopathy, treatment consists of controlling glucose levels, keeping blood pressure within a desired range, and limiting blood cholesterol. An exception is if macular edema has developed, in which case focal laser therapy is often very effective in preserving vision. Once blood vessels begin to appear during the proliferative stage, treatments include scatter laser therapy and vitrectomy. Investigational treatments are being pursued as well. See Diabetic Retinopathy: Treatment & Care for detailed information.
- Symptoms of Diabetic Retinopathy
- Diagnosing Diabetic Retinopathy
- Treatment & Care of Diabetic Retinopathy
- Diabetes, Vision Loss, & You
- Reducing the Risk of Diabetic Retinopathy