Today is World Diabetes Day, and this month is American Diabetes Month, so it seems like a great time to talk about diabetes! I would venture to guess that almost everyone reading this post either knows a person with diabetes or has diabetes themselves. According to the 2014 Center for Disease Control (CDC) National Diabetes Statistics Report, 9.3% of the US population has diabetes, and 27.8% of those with diabetes are undiagnosed. That means nearly 1 in 10 Americans have diabetes, and more than 1/4th of those with it don't know it. The increasing prevalence of diabetes has been referred to by many as a global epidemic. In this post, we'll briefly go over what diabetes is, and then we'll go into detail about how diabetes affects the eye.
What is diabetes? Diabetes is a group of diseases characterized by high blood glucose levels as a result of either a problem with how insulin is produced or how insulin works, or a combination of both. Glucose is the body's main source of energy, derived from the food we eat. Insulin is a hormone that allows glucose to be absorbed from the blood and converted to energy.
- In Type 1 diabetes, the body attacks the beta cells of the pancreas, which are responsible for producing insulin. As a result, the pancreas produces too little or no insulin. So a person with Type 1 diabetes depends on outside sources of insulin, such as insulin injections, insulin pumps, or even inhaled insulin, to be able to metabolize glucose. This type of diabetes is typically diagnosed early in life, and it accounts for about 5% (CDC) of diabetes cases.
- In Type 2 diabetes, the body either doesn't produce enough insulin or the cells of the body don't use the insulin produced properly. Most people with this type of diabetes are able to achieve blood glucose control with diet, physical activity, blood glucose monitoring, and oral medication as needed, although some require insulin therapy. Type 2 diabetes is usually diagnosed in adulthood, and accounts for 90-95% of all cases. Risk factors for Type 2 diabetes include a positive family history of the disease, being overweight, physical inactivity, age, ethnicity (African Americans, Hispanics/Latinos, Native Americans, Asian Americans and Pacific Islanders are at particularly high risk), a history of gestational diabetes, pre-diabetes, high blood pressure, and high cholesterol (AOA).
- Gestational diabetes is glucose intolerance experienced during pregnancy. It is typically diagnosed during the 2nd or 3rd trimester.
- Pre-diabetes is a term used to refer to above-normal blood glucose levels that are below the threshold for diagnosing diabetes. Intervention (ie: healthy diet, physical activity, weight loss) can reduce the rate of conversion from pre-diabetes to diabetes. In 2012, the CDC found that 37% of Americans 20 years of age and older fell into the pre-diabetes category in 2009-2012 (CDC).
How does diabetes affect the eye?
- The most common eye disorder associated with diabetes is diabetic retinopathy. Diabetic retinopathy is progressive damage to the small blood vessels that supply the tissue lining the inner surface of the eye (the retina). The AOA has some great videos to help illustrate the disease here. Diabetic retinopathy is the leading cause of new cases of blindness and low vision in Americans age 20 to 74 (AOA). In 2005–2008, of adults diabetics 40 years of age or older in the US, 28.5% had diabetic retinopathy, and 4.4% had advanced diabetic retinopathy—with conditions such as clinically significant macular edema and proliferative diabetic retinopathy—that could lead to severe vision loss (CDC).
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| Proliferative diabetic retinopathy |
- Non-proliferative diabetic retinopathy (NPDR) occurs when the capillaries of the retina balloon (microaneurysms) due to weakening of the vessel walls. They may leak blood (hemorrhages) and/or fat deposits (exudates) into the retina. NPDR is classified in 3 stages- mild, moderate or severe. No treatment is typically indicated for milder cases, unless there is clinically significant macular edema present. Frequent monitoring is imperative, as more severe cases may warrant treatment.
- Proliferative diabetic retinopathy (PDR) occurs when blood vessels that nourish the retina become blocked, shutting down the blood supply to parts of the retina. The retina then sends out signals to grow new blood vessels (neovascularization). These new vessels grow on the surface of the retina and/or into the gel-like substance that fills the back of the eye (the vitreous). These new vessels are bad news because they have weak, thin walls that can leak blood or cause scar tissue to grow. PDR has a high risk of vision loss if it is left untreated. Typical treatments may include scatter laser therapy (PRP), injecting medications into the eye (intravitreal injections), and/or removing and replacing the vitreous (vitrectomy).
- Macular edema results when the capillary walls weaken and allow fluid to leak into the area of the retina that is responsible for your central, sharpest vision (the macula). Macular edema can occur at any stage of diabetic retinopathy, and can even be present with 20/20 vision. Like PDR, macular edema has a high risk of vision loss if it is left untreated. Treatment for macular edema is typically intravitreal injections, and/or focal laser therapy if needed.
- Retinal cameras are used to take photographs of the retina (like the one seen above) in order to monitor retinopathy.
- Optical coherence tomography (OCT) can be used to evaluate how much swelling or edema is present. An OCT is a scanning laser that can assess the thickness of the retina.
- Fluorescein angiography (FA) may be ordered to evaluate leakage and guide treatment. A dye is injected into a vein in the arm and photos of the retina are taken as the dye reaches the retinal vessels.
- Other eye disorders associated with diabetes:
- A cataract is a clouding of the lens of the eye. It often develops earlier and progresses more rapidly in diabetics compared to non-diabetics (AOA).
- Eye movement disorders can occur secondary to diabetic neuropathy, resulting in double vision.
- The optic nerve can also be affected. There may be swelling (diabetic papillopathy) or damage due to insufficient blood supply (anterior ischemic optic neuropathy) (ADA).
- Diabetes can also cause blurred vision in the absence of all of the above. It is believed that high blood glucose levels cause increased fluid absorption in the lens of the eye, thus changing its shape and causing fluctuations in vision.
How often should a diabetic see their optometrist? Type 1 diabetics should have a dilated eye exam within 5 years of diagnosis, and at least yearly thereafter. Type 2 diabetics should have a dilated eye exam upon diagnosis, and at least yearly thereafter. Your optometrist may suggest more frequent examinations based on the presence and severity of diabetic eye disease, or they may refer you to a retinal specialist for treatment if indicated. The strongest predictor of diabetic retinopathy is the duration of diabetes, so it becomes increasingly important for diabetics to have regular eye exams. Do not wait for symptoms to see your eye doctor! Early intervention is key.
CliffsNotes: Diabetes is a multi-organ disease, and avoiding its complications takes a life-long commitment. Yearly dilated eye exams are an important part of that commitment.
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