Diabetes is a condition characterized by abnormally high levels of sugar in the blood. Chronic, uncontrolled blood glucose levels can damage the central nervous system, blood vessels and vital organs. The eye is also vulnerable among diabetics, susceptible to diseases such as glaucoma, cataracts and retinopathy, which is caused by reduced blood flow and abnormally high intraocular pressure.
Diabetic Retinopathy
According to the National Eye Institute (NEI), diabetic retinopathy is the leading cause of blindness among adults in the United States. It often causes no overt symptoms until serious vision loss has occurred. It develops when the retina--light-sensitive tissue in the back of the eye--becomes damaged due to inflamed or abnormal and weak blood vessels leaking fluid in the eye. Diabetic retinopathy develops in four stages. Its earliest stage--mild nonproliferative retinopathy, or NPR--is characterized by the occurrence of microaneurysms--small, balloon-like areas of swelling--in the blood vessels of the retina. The second stage--moderate NPR--is associated with progressive disease and blockage of blood vessels. Stage 3--severe NPR--involves the blockage of even more blood vessels, which deprives the retina of its blood supply and prompts the retina to stimulate growth of new blood vessels. During the last stage--proliferative retinopathy--abnormal and fragile new blood vessels grow on the retina and the surface of the clear gel that lines the eye. Leaking of blood from these vessels can initially cause specks of blood to appear "floating" in your vision; continued bleeding can cause severe vision loss or blindness.
Diabetic Macular Edema
Among those with diabetic retinopathy, blood vessels may leak fluid into the center of the retina, or macula, causing a condition known as diabetic macular edema, or DME. Diabetic macular edema causes blurred vision in the center of your visual field. According to the NEI, although DME can occur at any stage of retinopathy, it is more common with disease progression, and roughly half of those with proliferative retinopathy also have DME.
Cataracts
According to the American Diabetes Association, or ADA, people with diabetes are 60 percent more likely than those without diabetes to develop cataracts--a condition in which the normally clear lens of the eye becomes cloudy or darkly pigmented. While cataracts may not impair vision significantly early on, they typically cause blurred, dim or distorted vision as they grow larger. According to the Mayo Clinic, cataracts may also cause problems seeing clearly in dim light, sensitivity to light and glare, halos to appear around lights, a fading or yellowing of colors, double vision in one eye and the need for brighter light during reading and other activities. Treatment of cataracts typically involves surgery to remove and replace the affected lens.
Glaucoma
Glaucoma is a condition characterized by damage to the optic nerve of the eye as a result of abnormally high intraocular pressure. This pressure constricts blood vessels and restricts blood flow to the retina and optic nerve, leading to vision loss or blindness. People with diabetes are more than 40 percent more likely to suffer from glaucoma than people without diabetes, according to the ADA. Symptoms of glaucoma are often not noticeable until the condition is at an advanced stage. Depending upon the type of glaucoma, symptoms may vary considerably once they do develop. According to the Mayo Clinic, primary open-angle glaucoma can cause gradual loss of peripheral vision and tunnel vision, while acute angle-closure glaucoma can cause the acute onset of blurred vision, problems seeing in dim light, halos around lights, severe eye pain and nausea and vomiting.
