Diabetic retinopathy is a condition in which progressive damage to the blood vessels in the back of the eye leads to vision impairment or blindness. It causes legal blindness (20/200 or worse vision) in 12,000 to 24,000 Americans each year, according to the Centers for Disease Control and Prevention (CDC).

Scientists have recently found that diabetic retinopathy, as well as heart disease and the nerve disorder diabetic neuropathy, can develop in people with prediabetes. Follow-up research from the Diabetes Prevention Program (DPP) found that nearly 8 percent of prediabetic participants developed diabetic retinopathy during the three-year DPP. 

Diabetic retinopathy affects the retina, the light-sensitive structure at the back of the eye that transmits visual images to the brain. In normal vision, light enters the cornea (the clear front part of the eye) before passing through the pupil and lens and finally focusing on the retina. The retina acts like the film in a camera and records the image. Nerve cells in the retina then translate visual images into electrical impulses, which are sent on to the brain to be interpreted.

In diabetic retinopathy, high glucose (blood sugar) levels and other factors weaken the walls of the retinal capillaries (tiny blood vessels). The weak blood vessel walls allow blood to seep out of the vessel and into the eye. During the healing process, deposits called hard exudates cause a hardening that is visible to a physician. Exudates are fluids that pass through a vessel wall into adjoining tissues. They consist of cells, proteins and solid materials.

The hardening causes narrowing of the capillaries that provide nutrient-rich blood to the retina. The blockage prevents the nutrients from getting to the retina. As the retina becomes starved for oxygen and nutrients, the eye responds by stimulating the growth of abnormal new blood vessels. These vessels are weak and prone to leaking additional blood and fluid.

Diabetic retinopathy occurs in two major stages, which cause vision loss in different ways:

• Nonproliferative retinopathy or background retinopathy. Retinal blood vessels begin to deteriorate, becoming blocked or developing balloon-like deformities in the vessel walls called microaneurysms. The vessels may leak fluids, fats and proteins that collect in the central part of the retina (macula), causing it to swell. This condition is known as macular edema. Patients with nonproliferative retinopathy may experience blurred vision that impairs the visual sharpness needed for reading and detail work. Nonproliferative retinopathy can damage central vision, but peripheral (side) vision often continues to function.
  
  
• Proliferative retinopathy. Abnormal new blood vessels grow over the retinal surface. These vessels are fragile and tend to hemorrhage frequently, obscuring vision. This can affect both central and peripheral vision. Girls with type 1 diabetes have a higher risk of developing proliferative retinopathy than boys. Proliferative retinopathy can cause the following problems:
  
  
• Vitreous hemorrhage. Occurs when vessels grow toward and bleed into the clear, gel-like substance at the center of the eye called the vitreous. The severity of the hemorrhage and its location in the vitreous determines the degree of vision impairment. The blood released in a vitreous hemorrhage usually clears over time, and vision is sometimes restored to its pre-hemorrhage level. If this does not occur, the surgical removal of all or part of the vitreous (vitrectomy) may be necessary.
  
  
• Traction retinal detachment. The scar tissue resulting from neovascularization (growth of new blood vessels) sometimes shrinks. This can put tension on the retina and pull it from its normal location. This condition is known as a tractional retinal detachment, and it can cause severe vision loss. A vitrectomy and retinal reattachment procedure are necessary if vision is to be restored.
  
  
• Neovascular glaucoma. A form of glaucoma that results from the growth of abnormal blood vessels on the iris (the forward colored portion of the eye, surrounding the pupil). These vessels block fluid from leaving the eye, leading to a pressure buildup that can cause glaucoma.

Scientists have found diabetic retinopathy to be a strong predictor of the kidney disease diabetic nephropathy. This is both because of similar cause (hyperglycemia) and the fact that nephropathy exacerbates retinopathy. Both conditions are forms of diabetic angiopathy (diseases of blood vessels). Patients are advised to ask their physician about having periodic microalbuminuria tests to screen for kidney damage.

Patients with diabetes who keep tight control over glucose levels have a lesser risk of developing eye disease. Maintaining healthy blood pressure and cholesterol levels and a healthy body weight may also help to delay or prevent the development of eye disease.

Retinopathy is the term for the vascular disease seen in patients with diabetes. People with diabetes also have an increased risk of other eye disorders, including glaucoma, cataracts and diabetic optic neuropathy. 

Patients with diabetes should schedule an eye examination at least once a year with an ophthalmologist (a doctor who specializes in eye disease). An ophthalmologist is the only specialist who can detect, diagnose and treat diabetic retinopathy. Patients with type 1 diabetes should be seen at five years after diagnosis, and at least annually thereafter. Patients with type 2 diabetes should be seen at diagnosis, and at least annually thereafter.