Sweet Sight
Diabetes can put it in jeopardy

by Wilbur C. Blount, M.D., FACS, FICS
Sport Aviation - December 2001

Every day in the United States doctors diagnose 1,700 people with diabetes, a treatable disease where the body doesn’t produce enough insulin or use it properly. Most pilots know that in 1996 the FAA announced a new policy to allow the special issuance of third-class medical certificates to insulin-dependent (Type I) diabetics. But many pilots don’t know what diabetes is about, or its harmful effects.

For energy, the human body converts the food we eat into glucose, a sugar. The bloodstream carries glucose to our body’s cells, and insulin, a hormone, helps the glucose get into cells where it can be used for energy.

Diabetes occurs when the body doesn’t produce enough insulin or use it properly. When glucose cannot enter the cells, it builds up in the bloodstream. Over time, high blood glucose levels can damage the heart, blood vessels, kidneys, eyes, and nerves, leading to serious health problems.

There are two types of diabetes. Type I is an autoimmune illness in which people lack insulin because the body attacks its own insulin-producing cells in the pancreas. Type II is a condition in which the patient’s body does not use insulin efficiently or make enough of it. As with any disease, diabetes must be managed.

Diabetes & Vision
Sight is essential for pilots, and untreated diabetes can lead to a number of ocular diseases. Disturbance of the body’s glucose metabolism can lead to cataracts, a lens opacity that can reduce vision if it is dense enough. These lenses can be surgically removed and replaced with artificial lenses.

Glaucoma is elevated pressure inside the eye that can damage the optic nerve, and it occurs more frequently in people with diabetes than in the non-diabetic population. Medications or surgery can treat glaucoma.

Diabetic retinopathy refers to the number of changes that occur in the retina. They indicate that the patient has been exposed to high levels of blood glucose over time. If untreated, it may lead to blindness. These changes may be seen as early as the time when the diagnosis of diabetes is made.

Two types of diabetic retinopathy exist: nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR).

Commonly known as background retinopathy, NPDR is an early stage of diabetic retinopathy where tiny blood vessels leak blood or fluid, causing the retina to swell or form deposits called exudates.

Many diabetics have mild NPDR, which usually doesn’t affect their vision, but when it does, it is the result of macular edema and/or macular ischemia. Macular edema is swelling or thickening of the macula, a small area in the center of the retina that allows us to see fine details. It is the most common cause of visual loss in diabetic patients. Macular ischemia occurs when small blood vessels (capillaries) close, reducing the blood flow the macula needs to work properly. Blurry vision is the result.

PDR is present when abnormal new vessels (neovascularization) begin growing on the retina’s surface or optic nerve. Widespread closure of retinal blood vessels is the main cause of PDR. The retina responds to this reduced blood flow by growing new blood vessels in the area where the original vessels closed.

Unfortunately, the new (abnormal) vessels do not supply the retina with normal blood flow. The new vessels are often accompanied by scar tissue that may cause retinal wrinkling or detachment.

PDR causes visual loss in three ways. Vitreous hemorrhage happens when the fragile new vessels bleed into the vitreous, a clear, jelly-like substance that fills the center of the eye. If the hemorrhage is small, a person might see only a few dark floaters.

A large hemorrhage may reduce the vision to light perception. It may take days or months for the results of the hemorrhage to clear. If the eye does not clear the vitreous in a reasonable time, surgery can remove the vitreous hemorrhage.

Vitreous hemorrhage alone does not cause permanent vision loss. When the blood clears, visual acuity may return to its former level, unless the macula is damaged.

Traction retinal detachment occurs when scar tissue associated with neovascularization shrinks the retina, wrinkling and pulling it from its normal position. Macular wrinkling can cause visual distortion.

Neovascular glaucoma results when extensive retinal vessel closure causes new, abnormal blood vessels to grow on the iris (the colored part of the eye) and block the normal flow of fluid out of the eye. Pressure in the eye builds up, resulting in neovascular glaucoma, a severe eye disease that damages the optic nerve.

Visual Diagnosis

A medical eye examination is the only way to find changes inside the eye, and this is one reason why eye doctors dilate your eyes and peer into them with an ophthalmoscope. They can often diagnose and treat serious retinopathy before you’re aware of any vision problems.

When eye doctors find diabetic retinopathy, they may order color photographs of the retina or a special test, fluorescein angiography, to learn if you need treatment. In this test a dye is injected in your arm, and photos of your eye are taken to detect where fluid is leaking.

Prevention is the best treatment of diabetic retinopathy, and strict control of a diabetic’s blood sugar will significantly reduce the long-term risk of vision loss from diabetic retinopathy. If high blood pressure and kidney problems are present, they need to be treated.

Laser surgery is another treatment for people with macular edema, NPDR, PDR, and neovascular glaucoma because it seals blood vessels that are bleeding or leaking fluid.

For macular edema, the laser treatment’s main goal is to prevent further vision loss. It’s common for people who have blurred vision from macular edema to recover normal vision, but some may experience partial improvement.

For PDR, the laser is focused on all parts of the retina except the macula. This photocoagulation treatment causes abnormal new vessels to shrink and often prevents them from growing in the future. It also decreases the chance of vitreous bleeding.

Multiple laser treatments over time are sometimes necessary, and laser surgery doesn’t cure diabetic retinopathy and does not always prevent further loss of vision.

In advanced PDR, an eye doctor may recommend a vitrectomy, a microsurgical procedure that replaces the blood-filled vitreous with a clear solution. Doctors may wait up to a year to see if the blood clears on its own before performing a vitrectomy. Vitrectomy often prevents further bleeding by removing the abnormal vessels that caused the bleeding. If the retina is detached, it can be repaired during the vitrectomy surgery.

Preserving Vision
Vision loss is preventable. If you have diabetes, it is important to know it today. With improved diagnosis and treatment, only a small percentage of people who develop retinopathy have serious vision problems. Early detection of diabetic retinopathy is the best protection against loss of vision.

When people are first diagnosed with diabetes they should schedule an eye examination as soon as possible. And they should have an examination at least once a year, and more frequently if they’ve been diagnosed with diabetic retinopathy.

If diabetics need to be examined for glasses, it’s important that their blood sugar be in consistent control for several days when they see their eye doctor. Glasses that work well when the blood sugar is out of control will not work well when your sugar is stable. Rapid changes in blood sugar can cause fluctuating vision in both eyes even if retinopathy is not present.

You should have your eyes checked promptly if you have visual changes that affect only one eye, last more than a few days, or are not associated with a change in blood sugar levels. Diabetics may experience vision changes due to cataracts, glaucoma, and diabetic retinopathy. To maintain optimal vision acuity, all pilots should have periodic examinations.

Dr. Wilbur C. Blount, EAA 81194, is a member of the EAA Aeromedical Advisory Council and specializes in diseases and surgery of the retina and vitreous.

Diabetes Risk Factors
In the United States approximately 1,700 people are diagnosed with diabetes every day. You are at higher risk if:

• You are older than 45.
• You are overweight.
• You do not exercise regularly.
• You have a family history of diabetes.
• You are a woman who has had a baby that weighed more than 9 pounds at birth.

Warning Signs

• Extreme thirst
• Occasional blurry vision
• Frequent urination
• Unusual tiredness
• Unexplained weight loss
• Frequent or recurring skin, gum, or bladder infections
• Tingling/numbness in the hands or feet

Diabetes is treatable, but before it can be treated it must be diagnosed. If you have questions, consult your physician.