Here's yet another reason to carefully manage diabetes: It can cause a variety of eye diseases. One of them, diabetic retinopathy, is the leading cause of blindness in middle-aged Americans. 

Yale Medicine specialists make precise diagnoses of eye diseases related to diabetes. Some of them are deeply experienced in treating eye diseases and managing general health at the same time.

People who have diabetes for a long time and have poorly controlled blood sugar levels may develop disease in the retina (the light-sensitive layer at the back of the eye) called diabetic retinopathy. The term includes the conditions diabetic retinopathy, diabetic macular edema (DME), cataracts and glaucoma.

Diabetic retinopathy starts with some bleeding in the retina. As the condition progresses, leakage of fluid into the retina may lead to swelling of the surrounding tissue, including the macula, which is in the center of the retina. The swelling of the macula leads to diabetic macular edema, says Ron Adelman, MD, director of the Yale Medicine Retina & Vitreous Program.

DME is a consequence of diabetic retinopathy and can occur at any stage of diabetic retinopathy, although it is more likely to occur later as the disease goes on. Fluid buildup causes the macula to swell and thicken, which distorts vision.

The progression of this eye disease can result in the growth of abnormal blood vessels, which causes bleeding in the eye. If untreated, it can eventually lead to retinal detachment and loss of vision.

You may have heard that cataracts, a clouding of the eye’s lens, are often associated with older adults. Adults with diabetes are two to five times more likely than those without diabetes to develop cataracts, and it’s more likely to occur at an earlier age.

In adults, diabetes nearly doubles the risk of glaucoma, a disease that damages the optic nerve, which carries electrical impulses from the eye to the brain.

When this eye disease starts, there are often no symptoms. The patient would not notice without regular checkups with an ophthalmologist, says Dr. Adelman.

Even in the middle stages of this eye condition, patients may not know that they have it, so they need to have eye checkups regularly and manage their diabetes.

When it advances to moderate to severe stages, a patient will experience decreased vision. “The patient might notice that objects are blurry, or seeing objects in the distance, or reading feel difficult,” Dr. Adelman says.

Bleeding from abnormal blood vessels in the retina during early stages of diabetic retinopathy may cause the appearance of “floating” spots, but they sometimes clear on their own.

When fluid (edema) in the macula builds up, it leads to diabetic macular edema (DME). The macula is necessary for fine vision that you use for reading, recognizing faces, and driving. Although it is more likely to occur as diabetic retinopathy worsens, DME can happen at any stage of the disease.

Whether you developed diabetes as a child or as an adult, you are at risk for diabetic retinopathy, and the risk goes up the longer a patient has diabetes.

“Poorly controlled diabetes puts a patient at a higher risk,” says Dr. Adelman. “The higher the blood sugar levels, the worse the diabetes, the higher the risk. Also, when a patient’s hemoglobin A1C levels are high, there is higher risk of developing diabetic eye disease as well.” 

If your parents were diabetics and experienced diabetic eye disease, you’re also at a higher risk, Dr. Adelman says. Having high blood pressure and/or kidney disease are risk factors too.

Women who develop or have diabetes during pregnancy may have rapid onset or worsening of diabetic retinopathy.

When diabetics don’t manage their blood sugar levels properly, other health problems can ensue.

Chronically high blood sugar from diabetes can damage tiny blood vessels in the retina, leading to diabetic retinopathy. The retina detects light and converts it to signals sent through the optic nerve to the brain. Diabetic retinopathy can cause those blood vessels in the retina to leak fluid or bleed, distorting vision.

In its most advanced stage, new abnormal blood vessels grow on the surface of the retina, which can lead to scarring and cell loss in the retina.

Diabetic eye disease can cause bleeding inside the eye, which may lead to blindness and would require surgery. It can also cause the retina to detach. Also, the abnormal blood vessels can cause glaucoma, says Dr. Adelman.

Another, more serious condition is proliferative diabetic retinopathy, which can occur after the retinopathy progresses for a few years. When this happens, blood vessels are so damaged that they close off and new blood vessels begin growing in the retina, causing vision problems.

During an eye exam, an ophthalmologist may detect diabetic eye disease by doing the following tests:

• Visual acuity testing. This eye chart test measures a person’s ability to see at various distances.
• Tonometry. This test measures pressure inside the eye.
• Pupil dilation. Drops placed on the eye’s surface dilate (widen) the pupil, allowing a physician to examine the retina and optic nerve.
• Optical coherence tomography (OCT). This technique is similar to ultrasound but uses light waves instead of sound waves to capture images of tissues inside the body. OCT provides detailed images of tissues that can be penetrated by light, such as the eye.

After an eye doctor identifies the stage of a patient’s diabetic eye disease, a course of treatment is determined. If there is a diabetic macular edema, leading to decreased vision, treatment would involve the use of lasers or injections of steroids to reduce the swelling. 

Usually, patients will have monthly injections for about three months, and they generally notice improvement in their vision within one week to three months. Laser therapy uses the heat from a laser to seal or destroy leaking blood vessels in the retina.

If the diabetic eye disease has advanced and has caused severe and potentially permanent damage (such as retinal detachment), the patient may need surgery to fix those issues. At Yale Medicine, the patient will often come in for surgery in the morning and be out of the surgery center or hospital by early afternoon, Dr. Adelman says.

Even though diabetic retinopathy is the number one cause of blindness in middle-aged people, it's very preventable, says Dr. Adelman. When patients get to their doctors in a timely manner, and they have their eyes examined and treated, generally the disease shouldn’t advance to cause blindness.

“Get the teamwork approach from your diabetes doctor or primary care physician and ophthalmologist to work together,” Dr. Adelman says. “There are new advance treatments that are in clinical trials, and Yale Medicine offers some of those, in addition to a variety of treatment options for the patient. We also have diabetologists, diabetes specialists who are experts in controlling the general health of the patient and the eyes at the same time.”