Diabetes is the leading cause of blindness

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Dr J. C. Mangwiro
MMEd (UZ), MSc Diabetes Specialist Cardiff University (UK), FCP (ECSA)

If one has diabetes, regular visits to the ophthalmologist for eye exams are important to avoid eye problems. High blood sugar (glucose) increases the risk of diabetes eye problems. In fact, diabetes is the leading cause of blindness in adults age 20 to 74.

High blood sugar levels may cause temporary blurred vision. High blood sugar in diabetes causes the lens of the eye to swell, which changes the ability to see. To correct this kind of eye problem, there is need to get blood sugar back into the target range (90-130 milligrams per decilitre or mg/dl before meals, and less than 180 mg/dl one to two hours after a meal). It may take as long as three months after blood sugar is well controlled for vision to fully get back to normal.

Blurred vision can also be a symptom of more serious eye problems in people with diabetes. The three major eye problems that people with diabetes may develop and should be aware of are cataracts, glaucoma, and retinopathy.

Cataracts and Diabetes

A cataract is a clouding or fogging of the normally clear lens of the eye. The lens is what allows us to see and focus on an image just like a camera. Although anyone can get cataracts, people with diabetes get these eye problems at an earlier age than most and the condition progresses more rapidly than in people without diabetes.

If one has a cataract, there is a cloudy area in the lens of the eye that results in the inability to focus light, and vision is impaired.

Symptoms of this eye problem in diabetes include blurred or glared vision. This can be corrected through cataract extraction surgery during which the affected lens of the eye is replaced by a clear man-made lens.

Glaucoma and Diabetes

When fluid inside the eye does not drain properly from a build -up of pressure inside the eye, it results in another eye problem with diabetes called glaucoma. The pressure damages nerves and the vessels in the eye, causing changes in vision.

Treatment of open-angle glaucoma — the most common form of glaucoma — requires lowering the eye’s pressure by increasing the drainage of aqueous humor or decreasing the production of the fluid. Medications can accomplish both of these goals.

With open-angle glaucoma, there may be no symptoms of this eye problem at all until the disease is very advanced and there is significant vision loss. In the less common form of this eye problem, symptoms can include headaches, eye aches or pain, blurred vision, watering eyes, halos around lights, and loss of vision.

Treatment of this eye problem in diabetes can include special eye drops, laser procedures, medicine, or surgery. Surgery and laser treatments are directed at improving the eye’s aqueous drainage. Serious eye problems in diabetics can be prevented by getting regular annual glaucoma screening by an Ophthalmologist.

Diabetic Retinopathy

The retina is a group of specialised cells that convert light as it enters though the lens into images. The eye nerve or optic nerve transmits visual information to the brain.

Diabetic retinopathy is one of the vascular (blood-vessel related) complications related to diabetes. This diabetes eye problem is due to damage of small vessels and is called a ‘‘microvascular complication”.

The microvascular complications have, in numerous studies, been shown to be related to high blood sugar levels. The risk of these eye problems in diabetes complications can be greatly reduced by improving blood sugar control.

Diabetic retinopathy is the leading cause of irreversible blindness in industrialised nations. The duration of diabetes is the single most important risk for developing retinopathy. So the longer one has diabetes, the greater the risk of this very serious eye problem. If retinopathy is not diagnosed early or is not treated, it can lead to blindness.

People with type 1 diabetes rarely develop retinopathy before puberty. In adults with type 1 diabetes, it is also rare to see retinopathy before five years’ duration of diabetes.

The risks of retinal damage increase with progressive duration of diabetes. Intensive control of blood sugar levels will reduce your risks of developing retinopathy.

The DCCT, a large study of people with type 1 diabetes showed that people with diabetes who achieved tight control of their blood sugars with either an insulin pump or multiple daily injections of insulin were 50 percent-75 percent less likely to develop retinopathy, nephropathy (kidney disease), or nerve damage (all microvascular complications).

People with type 2 diabetes usually have signs of eye problems when diabetes is diagnosed. In this case, control of blood sugar, blood pressure, and blood cholesterol plays an important role in slowing the progression of retinopathy and other eye problems.

Types of Retinopathy in Diabetes:

  • Background retinopathy: Sometimes the blood vessel damage exists, but there is no vision problem. This is called background retinopathy. It’s important to carefully manage diabetes at this stage to prevent background retinopathy from progressing to more serious eye disease.
  • Maculopathy: In maculopathy, the person has developed damage in a critical area called the macula. Because this occurs in an area that is critical to vision, this type of eye problem can significantly reduce vision.
  • Proliferative retinopathy: New blood vessels start to grow in the back of the eye. Because retinopathy is a microvascular complication of diabetes, a disease of small vessels, this type of retinopathy develops because of an increasing lack of oxygen to the eye from vascular disease. Vessels in the eye are thinned and occluded and they start to remodel.

It is important to address the risk factors that can worsen the occluded vessels. Smoking cessation, high blood pressure control, cholesterol management, and blood sugar control must take place in order to stop the progression of new vessels from forming into the orbit of the eye.

These are fragile vessels that can bleed and eventually cause a clot to form in the orbit, which scars and causes detachment of the retina. This eventually leads to irreversible vision loss.

Treatment of diabetic retinopathy may involve laser procedures or surgery. In a study of people with diabetes with early retinopathy, laser therapy to burn the fragile vessel resulted in a 50 percent reduction of blindness.

To prevent retinopathy, it is pertinent to get regular eye screening by a specialist eye doctor annually. Women with diabetes who later become pregnant should have a comprehensive eye exam during the first trimester and close follow-up with an eye doctor during the rest of their pregnancy to avoid serious eye problems with diabetes. (This recommendation does not apply to women who develop gestational diabetes, since they are not at risk for retinopathy.)

Preventing Eye Problems  with Diabetes

  • The International Diabetes Association offers these eye care guidelines for people with diabetes to help prevent eye problems.
  • People with type 1 diabetes should have a dilated eye exam by an ophthalmologist or optometrist within three to five years after diagnosis.
  • People with type 2 diabetes should have a dilated eye exam by an ophthalmologist or optometrist shortly after diagnosis.
  • Annual eye exams should be done with both type 1 and type 2 diabetes by an ophthalmologist or optometrist; more frequently if necessary.
  • When considering pregnancy, women with a history of diabetes should have an eye exam prior and during pregnancy. This does not pertain to women with gestational diabetes.

To prevent eye problems in diabetes, one should:

  • Control blood sugar;
  • Control high blood pressure.

If you have diabetes, contact your doctor about any eye problems if any of the following occurs:

  • Black spots in your vision;
  • Flashes of light;
  • Holes in your vision;
  • Blurred vision.

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