AND HOW DIABETES CAN AFFECT SIGHT: BY THE AMERICAN ACADEMY OF OPHTHALMOLOGY
Diabetes mellitus is a condition which impairs the body's ability to use and store sugar. Elevated blood-sugar levels, excessive thirst and urination, and changes in the body's blood vessels are all characteristics of the disease. Diabetes may affect vision by causing cataracts, glaucoma and, most importantly, damage to blood vessels inside the eye.
What Is Diabetic Retinopathy?
Diabetic retinopathy, a complication of diabetes, is caused by changes in the blood vessels of the retina, the light-sensing nerve layer in the rear of the eye. These damaged blood vessels may leak fluid or blood, and develop fragile brush-like branches and scar tissue. The images that the retina sends to the brain become blurred, distorted or partially blocked.
The risk of developing diabetic retinopathy increases the longer a person has diabetes. About 80% of the people with at least a 15-year history of diabetes have some blood vessel damage to their retina.
Diabetic retinopathy is particularly likely to occur at a younger age in juvenile diabetics, who have been diagnosed with the condition during their childhood or teenage years. Diabetic retinopathy is the leading cause of new blindness among adults in the United States and people with untreated diabetes are said to be 25 times more prone to blindness than the general population. However, with 'improved methods of diagnosis and treatment only a small percentage of those who develop retinopathy experience serious problems with vision.
Types of Diabetic Retinopathy
Background retinopathy is an early stage of diabetic retinopathy. In this stage, fine blood vessels within the retina become narrowed or obstructed while others enlarge to form balloon-like sacs. These altered vessels leak blood and fluid, causing the retina to swell or form deposits called exudates. Sight is usually not seriously affected. It can however lead to more advanced sight-threatening stages and for this reason is considered a warning sign.
In some cases, the leaking fluid collects in the macula, the portion of the retina responsible for detailed vision, such as reading. This problem is called macular edema. Reading and close work may become more difficult because of this condition. Edema is the most common cause of visual loss in diabetes. Vision loss may be mild or severe, but peripheral vision continues to function. In more severe cases, macular ischemia occurs when small blood vessels (capillaries) close. Vision blurs because the macula no longer receives sufficient blood supply to work properly.
Proliferative retinopathy describes the changes that occur when new, abnormal blood vessels begin growing on the surface of the retina or the optic nerve due to the widespread closure of retinal blood vessels (ischemia). The retina is attempting to re-supply blood to the area where the original vessels closed. These new blood vessels, called neovascularization, have weaker walls and may rupture and bleed into the vitreous, the clear gel-like substance that fills the center of the eye. This leaking blood (vitreous hemorrhage) can cloud the vitreous and partially block the light passing through the pupil towards the retina, causing floaters or blurred and distorted images. It may take days, months, or even years to resorb the blood. If the eye does not clear the blood within a reasonable time, a vitrectomy surgery may be recommended.
These abnormal blood vessels frequently grow scar tissue with them, which may pull the retina away from its normal position at the back of the eye (tractional retinal detachment). Macular wrinkling can cause visual distortion. Severe vision loss can occur if the macula or large areas of the retina are detached. Abnormal blood vessels may also grow around the pupil and onto the iris (the colored part of the eye) causing neovascular glaucoma. These new vessels block the normal flow of fluid out of the eye, therefore causing an increase in pressure within the eye. Neovascular glaucoma is a severe eye disease that causes damage to the optic nerve.
Proliferative diabetic retinopathy is the most serious form of diabetic retinal disease. It affects up to 20% of diabetics and can cause severe loss of sight, including blindness.
Cause and Symptoms
The cause of diabetic retinopathy is not completely understood; however, it is known that diabetes damages small blood vessels in various areas of the body. Pregnancy and high blood pressure may aggravate diabetic retinopathy.
Although gradual blurring of vision may occur if macular edema is present; sight is usually unaffected by background diabetic retinopathy and changes in the eye can go unnoticed unless detected by a medical eye examination. When bleeding occurs in proliferative retinopathy, the sight may become hazy, sporty or even disappear altogether. While there is no pain, this severe form of diabetic retinopathy requires immediate medical attention.
Detection and Diagnosis
A comprehensive medical eye examination and appropriate treatment by an ophthalmologist is the best protection against eye damage due to diabetic retinopathy. Serious retinopathy can be present without symptoms and improve with treatment. Therefore, people with diabetes should be aware of the risks of developing visual problems and should have their eyes examined regularly. (Periodic eye examinations are also advisable for apparently healthy people, because such examinations help detect the presence of diabetes and other diseases.)
To detect diabetic retinopathy, the ophthalmologist conducts a painless examination of the inner part of the eye using an instrument called an ophthalmoscope. The pupils may need to be dilated with eye drops.
If diabetic retinopathy is noted, the ophthalmologist may obtain color photographs of the retina. Sometimes a specialized technique is used which provides great detail about retinal blood vessels and leakage. First, a fluorescent dye is injected into a vein in the arm. The dye travels through the bloodstream, including the blood vessels of the retina. Photographs are taken in rapid succession as the dye passes through the retinal blood vessels. This technique, called fluorescein angiography, is often used by ophthalmologists to determine if further treatment is necessary.
The best treatment is to prevent the development of retinopathy through strict control of your blood sugar. This can significantly reduce the long-term risk of vision loss from diabetes. High blood pressure and kidney problems also need to be treated.
When diabetic retinopathy is diagnosed, the ophthalmologist considers the patient's age, history, lifestyle, and the degree of damage to the retina before deciding whether treatment or further observation of the disease is most appropriate. In many cases, treatment is not necessary; in others, laser or surgical treatment is recommended to halt the damage of diabetic retinopathy and to improve sight wherever possible.