Diabetic macular edema (DME) is a buildup of fluid in the central part of the retina, called the macula, caused by diabetes. It affects roughly 3.8% of U.S. adults over 40 who have diabetes, making it one of the leading causes of vision loss in people with the disease. DME can develop at any stage of diabetic retinopathy and, without treatment, carries a 24% risk of moderate vision loss over three years.
How DME Differs From Diabetic Retinopathy
Diabetic retinopathy is a broad term for all the damage diabetes does to blood vessels throughout the retina. It shows up as tiny hemorrhages, microaneurysms, cotton wool spots, and, in advanced stages, abnormal new blood vessel growth. DME is a more specific problem: fluid leaking into the macula, the small area responsible for sharp, central vision. You can have diabetic retinopathy without macular edema, and the severity of one doesn’t always predict the other.
This distinction matters because the two conditions can require different treatments and have different consequences. Retinopathy can damage the peripheral retina without affecting day-to-day vision for a long time. DME, by contrast, strikes at the center of your visual field, where you read, recognize faces, and drive.
What Happens Inside the Eye
Your retina is protected by a structure called the blood-retinal barrier, a set of tightly sealed cell layers that control what passes from the bloodstream into retinal tissue. In a healthy eye, proteins, salts, and other large molecules stay in the blood where they belong. Chronic high blood sugar disrupts this barrier.
The key player is a signaling protein called VEGF-A (vascular endothelial growth factor). When blood sugar remains elevated, VEGF levels rise in the fluid inside the eye. VEGF loosens the junctions between cells lining the retinal blood vessels in at least two ways: it triggers chemical changes that pull apart the seal between neighboring cells, and it increases the number of tiny transport bubbles that shuttle fluid from inside the vessel out into the surrounding tissue. The result is that proteins and water leak into the macula, causing it to swell. That swelling distorts or destroys the light-sensing cells you rely on for central vision.
Inflammation compounds the problem. Inflammatory molecules rise alongside VEGF, further weakening the barrier and promoting chronic damage. Importantly, research shows that even after the fluid clears, retinal nerve cells may already be lost. This is why early detection and treatment matter so much: reducing swelling doesn’t always restore vision if neurons have already died.
Risk Factors
Poorly controlled blood sugar is the strongest modifiable risk factor. Research has found that people with an HbA1c of 8% or higher have significantly greater macular thickening compared to those with better glucose control. Younger age (50 and under) also showed a positive association with thicker maculas in diabetic eyes, possibly because younger patients may have had more aggressive disease or longer periods of poor control relative to their age.
Other established risk factors include high blood pressure, high cholesterol, longer duration of diabetes, and the presence of more advanced diabetic retinopathy. Kidney disease, which often accompanies diabetes, further raises the risk.
Symptoms and What You Notice
DME can be sneaky. If the swelling hasn’t reached the very center of the macula, you may have no symptoms at all. Only very observant people might notice a small blank or dark spot near the center of their vision corresponding to a pocket of fluid or fatty deposits.
Once the center is involved, symptoms become harder to ignore. You may notice that straight lines look wavy or distorted, a phenomenon called metamorphopsia. Colors can appear washed out or harder to distinguish. Some people describe poor night vision, difficulty adjusting between bright and dark environments, or a general haziness across their central vision. These changes tend to develop gradually, which is why regular eye exams catch DME far earlier than symptoms alone.
How DME Is Diagnosed
The gold standard for diagnosing DME is optical coherence tomography (OCT), a painless imaging scan that creates a detailed cross-section of your retina in seconds. The scan reveals pockets of fluid within or beneath the retinal layers and measures retinal thickness down to the micrometer. Center-involved DME, the type most likely to threaten vision, is generally defined as a central retinal thickness of 250 micrometers or greater.
Your eye doctor may also use a dilated eye exam to look for hard exudates (yellowish fatty deposits) near the center of the macula, which serve as a visible marker of leakage. Fluorescein angiography, where a dye is injected into your arm and photographed as it passes through retinal blood vessels, can pinpoint exactly where leakage is occurring. In practice, OCT findings combined with visual acuity testing are what most clinicians use to decide whether treatment is needed.
Treatment With Eye Injections
The first-line treatment for center-involved DME is a series of injections directly into the eye. These injections deliver drugs that block VEGF, the protein driving the fluid leakage. The procedure sounds alarming, but the eye is numbed with drops beforehand, and most people describe feeling pressure rather than sharp pain.
Treatment typically starts with a loading phase of three monthly injections. After that, your doctor assesses how well the fluid is resolving and adjusts the schedule. Many clinics use a “treat and extend” approach, gradually lengthening the time between injections as long as the macula stays dry. Clinical trials using this method have shown vision improvements of roughly 6 to 10 letters on an eye chart. Some people eventually reach a point where injections can be stopped, while others need ongoing treatment to keep the fluid from returning.
The newer drug faricimab works on two targets at once, blocking both VEGF and a second protein involved in blood vessel instability. This dual action may allow longer intervals between injections for some patients.
When Steroid Implants Are Used
For people whose DME doesn’t respond well to VEGF-blocking injections, or who can’t maintain frequent clinic visits, steroid implants offer an alternative. These are tiny devices placed inside the eye that slowly release an anti-inflammatory medication over weeks to months. Their main advantage is duration: a single implant can work for roughly three months, and some sustained-release versions are designed to last up to three years.
Steroid implants are particularly useful for people who have already had cataract surgery (since steroids can accelerate cataract formation, and that’s no longer a concern once the natural lens is gone), those with long-standing DME, and patients in settings where frequent monthly visits aren’t practical. The trade-off is a higher risk of increased eye pressure, which needs monitoring.
What Happens Without Treatment
Left untreated, DME carries a roughly 24% chance of moderate vision loss over three years. “Moderate” in clinical terms means losing enough acuity to drop from, say, 20/20 to 20/40, or equivalently, three lines on a standard eye chart. Laser treatment, which was the standard before injectable therapies, cuts that risk in half. Current VEGF-blocking treatments do even better, often improving vision rather than just preserving it.
The longer DME goes untreated, the more likely it is that retinal neurons will be permanently damaged. Even if the fluid is eventually cleared, vision may not fully recover once those cells are gone. This is why screening matters: annual dilated eye exams for anyone with diabetes can catch DME before it causes noticeable symptoms, when treatment is most effective.