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Diagnosing Diabetic Macular Edema: What Is OCT?

Medically reviewed by Sarika Chaudhari, M.D., Ph.D.
Posted on November 1, 2023

  • Diabetic macular edema (DME) is a relatively common vision problem in people with diabetes.
  • Optical coherence tomography (OCT) is a type of scan used by an eye doctor to determine tissue thickness.
  • Early detection and treatment of DME can prevent blindness.

Although taking care of your vision may not seem like a top priority when managing type 2 diabetes, it is. Vision problems that can lead to blindness are a common complication of diabetes. When they’re caught early, however, they’re often treatable.

This article will discuss one type of vision problem found in diabetes: diabetic macular edema. We will review the best way to diagnose DME using optical coherence tomography. Ultimately, yearly checkups with an ophthalmologist (eye doctor) can help prevent worsening symptoms and vision loss.

What Is Diabetic Macular Edema?

DME is macular edema caused by diabetes. The macula is part of the eye responsible for focusing on the things in front of you. It is located at the back of the eye in a layer of tissue called the retina. The retina processes all of your visual surroundings, which includes your direct line of focus and everything in the periphery. The word “edema” means swelling, and macular edema is swelling of the macula.

DME is relatively common in diabetes. Up to 7 percent of individuals with diabetes develop DME. Blurred vision is a common symptom of DME. One DiabetesTeam member shared, “When my blood sugar is high, my vision can be blurry.”

Other symptoms include:

  • Floaters — Spots that float around in your vision
  • Wavy vision
  • Light sensitivity
  • Headaches
  • Trouble focusing and reading

Another DiabetesTeam member described their experience with floaters: “I have a bubble type of floater that appears in my eye. It floats across my line of sight.”

More than 50 percent of all people with diabetes develop diabetic retinopathy. In this condition, capillaries (small blood vessels) in the retina become damaged because of high blood glucose (sugar). During diabetic retinopathy, the vessels in the retina start to leak fluids and fats. These vessels also release inflammatory chemicals that further irritate the retina. One of these chemicals is called vascular endothelial growth factor (VEGF), which forms new, abnormal blood vessels.

Because of the leakage of chemicals, fluids, and fats, diabetic retinopathy can cause DME. These substances damage the tissue. Fluid accumulation can lead to swelling and enlargement of the retina and the macula. When the fats can bond together and aren’t cleared, they create what’s known as hard exudates. Together, the swelling and exudates lead to macular thickening and retinal thickening.

How Is DME Diagnosed?

Diagnosing DME early is important, as effective treatments are available to prevent vision loss. An ophthalmologist can diagnose DME through an eye exam. During this exam, they put drops in your eyes to dilate (open up) your pupils, which allows them to shine a light into your eye and look directly at your retina.

Other diagnostic tests are also needed to confirm a DME diagnosis. The standard of care is a technique called optical coherence tomography, covered more extensively below. A doctor may also use a test called fluorescein angiography. For this test, they’ll inject a dye into a vein — most often in the arm — which will travel through the body up to the retina. Your doctor will be able to use a specific camera to examine the blood vessels in your retina.

Sometimes, in DME and diabetic retinopathy, the capillaries in the eye start to grow more than they should. Fluorescein angiography can help your doctor see if there are additional capillaries. It can also show any abnormal changes in the blood vessels or signs of leakage.

Optical Coherence Tomography

An eye doctor can use optical coherence tomography to produce high-quality 3D images of your retina. The technology is the standard for diagnosing and monitoring diabetic macular edema. (Adobe Stock)

OCT is the cornerstone for diagnosing and monitoring DME because it measures macular thickness and retinal thickness. OCT is a high-resolution imaging technique. It passes near-infrared (long wavelength) light into your eye at your retina to produce a 3D image of your retina. The light from the machine goes into your eye and bounces back to the detector. Another light goes through a different path. The difference in time between when the light from your eyes reaches the detector and when the other light path reaches the detector is called interference. This interference helps create the image. The timing will be different as the light passes through different surfaces of different materials. For example, areas with exudates and fluid buildup will be different from a healthy retina.

People with cataracts may have a harder time getting diagnosed using OCT. Cataracts are deposits in the lens of the eye that make it cloudy. Normally, the lens in the eye is clear, allowing light to enter and focus on the retina. A cataract blurs the entry point of the light from the imager in the OCT procedure. Also, bleeding in the back side of the eye, known as vitreous hemorrhage, can hamper the image quality obtained by OCT.

During an OCT scan, you’ll first have drops put in your eyes to dilate your pupils to allow more light to enter. After a few minutes, you’ll rest your chin on the OCT machine to keep your head still. You’ll keep your eyes focused on a point while the machine takes a series of pictures of your retina. Each eye will be imaged individually. The test will take up to 10 minutes.

Center-Involved or Non-Center-Involved DME

There are a number of ways that DME can be described based on different characteristics, including “center-involved” or “non-center-involved.” In center-involved DME, swelling has occurred in the center of the macula, known as the fovea. This affects your central vision (ability to focus on things in front of you). Non-center-involved DME means that the swelling has occurred outside of the fovea. This is visible on an OCT scan because it shows multiple dimensions of the retina.

In center-involved DME, swelling takes place at the fovea in the center of the macula, where your eyesight is sharpest. (Adobe Stock)

Other characteristics of DME can also be picked up on an OCT scan, such as retinal disorganization. This is when the retinal layers — layers of cells in the retina — are no longer organized correctly. OCT will give mapping of the thickness of the retina, areas where fluid is trapped in the layers of retina, and changes in the fovea, among other things. It’s also very helpful for monitoring how DME treatment is working.

Talk to Your Doctor

If you have diabetes and are experiencing problems with your eyesight, talk to your doctor. Health experts generally recommended that people with diabetes follow up with an eye doctor every year to check for retina damage and vision problems.

Find Your Team

DiabetesTeam is the social network for people with diabetes and their loved ones. On DiabetesTeam, more than 139,000 members come together to ask questions, give advice, and share their stories with others who understand life with diabetes.

Do you have DME or diabetic retinopathy? Were you diagnosed with OCT? Share your experience in the comments below, or start a conversation by posting on your Activities page.

Posted on November 1, 2023
All updates must be accompanied by text or a picture.

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Sarika Chaudhari, M.D., Ph.D. completed her medical school and residency training in clinical physiology at Government Medical College, Nagpur, India. Learn more about her here.
Hannah Actor-Engel, Ph.D. is a multidisciplinary neuroscientist who is passionate about scientific communication and improving global health through biomedical research. Learn more about her here.

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