Diabetic retinal oedema is a serious eye complication that develops when high blood sugar damages the tiny blood vessels in the back of the eye, causing fluid to leak and accumulate in the macula. This swelling in the central part of your retina can blur your vision and, without proper care, lead to significant vision loss. Understanding when and how to get tested can make all the difference in protecting your sight.

Introduction: Who Should Seek Testing and When

If you have diabetes, you are automatically at risk for developing diabetic retinal oedema, also called diabetic macular edema. This condition doesn’t usually announce itself with pain or obvious warning signs in its early stages. Many people discover they have it during a routine eye examination before they even notice vision problems. That’s why regular eye testing is not just recommended—it’s essential for anyone living with diabetes.^[1]

You should seek diagnostic testing right away if you notice sudden changes in your vision. Warning signs include blurred or wavy vision, dark spots appearing in your field of view (especially first thing in the morning), difficulty reading, colors appearing faded or washed out, straight lines that look bent or curved (like door frames or lamp posts), trouble seeing in bright light or glare, or objects that seem to change size when you switch from viewing with one eye to the other.^[1][3] Any of these symptoms warrants immediate contact with your eye care provider.

Even if you have no symptoms at all, you need to have your eyes checked regularly. People with diabetes should attend annual diabetic eye screening appointments to reduce their risk of vision loss.^[3] If you’ve been diagnosed with diabetic retinopathy—damage to the blood vessels in your retina caused by diabetes—you may need more frequent examinations, as diabetic retinal oedema is a complication of this condition.^[6]

If you’re pregnant and have diabetes—or develop gestational diabetes during pregnancy—your healthcare team may recommend additional eye examinations throughout your pregnancy. Pregnancy can increase the risk of developing diabetic retinal problems or make existing problems worse.^[7]

Diagnostic Methods for Identifying Diabetic Retinal Oedema

You cannot see swelling in your own retina just by looking in the mirror, but your eye care specialist can detect it during a thorough examination. This is one of the most important reasons to keep your regular eye exam appointments, especially when you have diabetes.^[1]

The diagnostic process typically begins with a comprehensive eye examination. Your eye care provider will start by checking your visual acuity—how well you can see at various distances. This simple test measures whether your vision has changed and by how much.^[8]

A critical part of diagnosing diabetic retinal oedema involves dilating your pupils. Your doctor will place special drops in your eyes that widen your pupils, allowing them to get a much better view of the structures inside your eye, particularly your retina and macula. The drops can make your near vision blurry for several hours, so it’s wise to bring someone along to drive you home after the appointment.^[10]

During the dilated examination, your provider will use a slit lamp—a specialized microscope with a bright light—to examine the inside and outside parts of your eyes. They’ll look for irregularities in your retina and signs that fluid has accumulated in the macula.^[1][10]

Beyond the basic eye exam, several specialized imaging tests help diagnose and monitor diabetic retinal oedema. One of the most important is optical coherence tomography, commonly called OCT. This painless imaging test creates detailed cross-sectional pictures of your retina, showing its anatomy and thickness. The OCT reveals exactly how much fluid, if any, has leaked into the retinal tissue. It works somewhat like an ultrasound but uses light waves instead of sound waves. Later, your doctor can use follow-up OCT scans to check whether treatment is working by comparing the thickness of your retina over time.^[1][8][10]

Another valuable test is fluorescein angiography. After your eyes are dilated, your doctor injects a special yellow-orange dye called fluorescein into a vein in your arm. As the dye circulates through your bloodstream, it travels to the blood vessels in your eyes. A specialized camera takes pictures as the dye moves through these vessels, highlighting areas where blood vessels are closed, broken, or leaking fluid. These pictures help your doctor pinpoint exactly which blood vessels are damaged and causing the fluid buildup in your macula.^[1][8][10]

Your provider may also use an Amsler grid test, which uses a pattern of horizontal and vertical lines to check your central vision. When you look at the grid, you’ll be asked to describe what you see. If you have diabetic retinal oedema, the straight lines may appear wavy, distorted, or broken.^[1][8]

These diagnostic tests work together to give your doctor a complete picture of what’s happening inside your eye. The comprehensive eye exam reveals whether you have diabetic retinal oedema, while the imaging tests show how severe it is and which specific areas are affected. This information is crucial for determining the best treatment approach and tracking whether the condition is improving, staying stable, or getting worse over time.

Diagnostics for Clinical Trial Qualification

When patients with diabetic retinal oedema are being considered for enrollment in clinical trials, researchers use specific tests and criteria to determine who qualifies. While the exact requirements vary from one study to another, certain standard diagnostic procedures are commonly used to establish eligibility.

Visual acuity testing is typically a key qualification criterion. Clinical trials often specify that participants must have vision within a certain range—for example, vision of 20/50 or worse in the affected eye. This ensures the study includes patients who have meaningful vision loss that could potentially improve with treatment. Researchers measure visual acuity using standardized charts and protocols to ensure consistent measurements across all participants.^[12]

Optical coherence tomography scans are standard tools for trial qualification because they provide objective, measurable data about retinal thickness. Researchers can use OCT to measure exactly how much swelling is present in the macula and track changes over time with great precision. Many clinical trials set specific thresholds for retinal thickness—participants must have swelling that exceeds a certain measurement to qualify. The OCT also helps researchers identify and exclude patients who have other eye conditions that might interfere with the study results.^[1][8]

Fluorescein angiography is another diagnostic test frequently used in clinical trial screening. This test helps researchers confirm that fluid leakage is occurring and identify the pattern and severity of blood vessel damage. The detailed images from fluorescein angiography allow researchers to classify patients according to the type and extent of their diabetic retinal disease, which is important for matching patients to appropriate studies.^[1][8]

In addition to eye-specific tests, clinical trials typically require documentation of a patient’s diabetes diagnosis and history. Researchers need to know how long someone has had diabetes, what type of diabetes they have (type 1 or type 2), and how well controlled their blood sugar levels are. Blood tests measuring hemoglobin A1c—a marker of average blood sugar over the past few months—are commonly part of the screening process.

The diagnostic process for trial qualification is usually more extensive than a regular eye exam. Researchers need detailed baseline information about each participant’s condition before treatment begins, so they can accurately measure any changes that occur during the study. This often means repeating some tests multiple times to establish consistent baseline measurements.