How Does Diabetes Lead to Blindness?

People with diabetes have a higher risk of blindness than people who do not have diabetes.

That said, people with well-controlled diabetes are likely to suffer only minimal complications with their eyes.

The Anatomy of the Eye

The eye is a rounded, vitreous-fluid-filled ball. At the front of the eye is the cornea, which serves as a protection for the eye at the same time as it focuses light. Behind the cornea is the aqueous humor, a protective fluid that separates the cornea from the pupil.

The pupil is the hole in the center of the iris, the colored portion of the eye. The pupil dilates and contracts, controlling the amount of light that enters the inside of the eye. Behind the pupil is another lens, which aids in focusing images.

Light and images continue to pass through the vitreous fluid in the interior of the eyeball, until they hit the retina. The retina sits at the back of the eye and serves to focus images and code them for the brain to interpret.

One portion of the retina, called the macula, is used to see fine detail. This area of the retina is the site of many blood vessels, which nourish the retina.

How Diabetes Affects the Eyes

Because diabetes is a disease that can cause serious damage to the endothelial cells that line blood vessels, and because the eye is full of tiny blood vessels, the risk of damage to these vessels resulting in eye disorders is greater in those with diabetes.

The same types of damage that can occur elsewhere in the body - hardening of blood vessels, inflammation due to the disruption of the protective endothelial cells - can also occur in the eyes, which can trigger various responses.

Diseases of the Eye

Diabetics are 40 percent more likely to suffer glaucoma and 60 percent more likely to suffer cataracts than people without diabetes. The risk of glaucoma continues to increase with age, while the incidence of cataracts tends to increase at a younger age for diabetics than non-diabetics.

Glaucoma results from increased pressure within the eye, interfering with drainage of vitreous fluid and creating an impingement of the blood vessels that serve the retina and the optic nerve. This, in turn, can lead to gradually reduced vision and eventually blindness.

There are treatments for glaucoma, including medications to reduce pressure and surgery for more advanced cases.

Cataracts result from the clouding of the clear lens at the front of the eye, which reduces vision. Surgery can remove the clouded lens and replace it. The downside of surgical repair for the diabetic is that glaucoma may begin to develop and retinopathy may worsen.

Diabetic retinopathy is a general term that refers to damage to the retinal surface and related blood vessels which results from poorly controlled diabetes. Retinopathy can be proliferative or non-proliferative.

Two Types of Diabetic Retinopathy

The most common form of retinopathy is non-proliferative. In this form, capillaries at the back of the retina, damaged by high glucose levels, swell up and form small aneurysms, which are balloon-like pouches. While this does not generally cause vision loss, it can lead to macular edema.

Macular edema is the result of fluid leaking from these damaged capillaries into the macula, causing swelling. Because the macula is the part of the eye that focuses fine images, this leakage can result in blurring of vision, or possible loss of vision. Macular edema must be treated to avoid vision loss, but treatment is generally effective.

Proliferative retinopathy can develop after several years of damage to the retina.In this form, the blood vessels are so damaged that they cease to work. New vessels develop to compensate, but these vessels are not healthy. They can leak blood into the retina, blocking vision. This is called vitreous hemorrhage. Scar tissue can also grow, causing distortion to the retina or even causing the retina to detach.

There are medical and surgical treatments for this. A detached retina is an emergency, and the patient should contact their doctor

Annual Eye Exams Recommended

The worst part about eye diseases is that they are silent in their early stages, when they are most able to be treated successfully. The American Diabetes Association and the National Eye Institute recommend that every person with diabetes - whether type 1 diabetes or type 2 diabetes - have an annual eye exam with dilation, in order to spot problems before they cause permanent damage.

Sources: American Diabetes Association and National Eye Institute

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