Diabetic macular edema is fluid accumulation in the central retina caused by leaky capillaries in diabetic retinopathy. It is the most common cause of vision loss in working-age people with diabetes and presents with blurry central vision and wavy straight lines. Diagnosis relies on optical coherence tomography (OCT), and treatment now centers on anti-VEGF injections — aflibercept, ranibizumab, bevacizumab, faricimab, and brolucizumab — which have largely replaced focal laser as first-line therapy. Strict control of glucose, blood pressure, and lipids is the foundation.
What Diabetic Macular Edema Is
Diabetic macular edema (DME) develops when the small blood vessels in the retina become leaky because of chronic hyperglycemia. Fluid and proteins escape into the macula — the central part of the retina responsible for sharp, detailed vision. The macula thickens, the photoreceptors lose their precise architecture, and central vision blurs. DME can occur with non-proliferative or proliferative diabetic retinopathy and is the leading reason that working-age diabetics lose vision.
About 7 percent of people with diabetes have some degree of DME, and the prevalence rises with disease duration and poorer glycemic control. Type 1 diabetics typically develop DME after 10 to 15 years; type 2 diabetics can have it at diagnosis if they have been hyperglycemic undetected for years.
Why It Happens
- Chronic hyperglycemia damages retinal capillary endothelium and pericytes
- Breakdown of the inner blood-retinal barrier allows fluid leakage
- Vascular endothelial growth factor (VEGF) is upregulated and increases permeability
- Inflammatory cytokines (IL-6, IL-8, ICAM-1) amplify the leak
- Microaneurysms and dilated capillaries leak focally; broader ischemia causes diffuse leakage
- Hypertension, dyslipidemia, kidney disease, and pregnancy worsen DME
Risk Factors
- Long-duration diabetes (type 1 or type 2)
- Higher A1C — see our A1C levels guide
- Hypertension
- Dyslipidemia (especially elevated triglycerides and lipid exudates)
- Chronic kidney disease and proteinuria
- Pregnancy in someone with existing retinopathy
- Rapid glycemic improvement (paradoxical worsening early on)
- Smoking
Classification
| Type | Features |
|---|---|
| Focal DME | Localized leak from microaneurysms; circinate ring of exudates |
| Diffuse DME | Widespread capillary leakage; less defined exudate |
| Cystoid DME | Pockets of fluid forming cyst-like spaces on OCT |
| Center-involved DME (CI-DME) | Edema involves the foveal center — most likely to affect vision |
| Non-center-involved DME | Macula thickened but fovea spared |
Symptoms
- Gradual blurring of central vision
- Metamorphopsia — straight lines appear curved
- Difficulty reading and recognizing faces
- Dull or washed-out colors
- Floaters less common in DME alone (more typical of proliferative retinopathy)
- Peripheral vision usually preserved
- Sometimes no symptoms in early or non-center-involved disease
Diagnosis
Dilated Eye Exam
- Pupils dilated with drops
- Indirect ophthalmoscopy and slit-lamp biomicroscopy
- Look for microaneurysms, hard exudates, and thickening near the macula
Optical Coherence Tomography (OCT)
- Non-invasive cross-sectional retinal imaging
- Quantifies retinal thickness in microns
- Identifies intraretinal fluid, cysts, and subretinal fluid
- Standard test for follow-up of response to injections
- Can be performed in a few minutes per eye
Fluorescein Angiography
- Intravenous fluorescein dye and serial retinal photography
- Identifies leaking microaneurysms and areas of capillary non-perfusion
- Useful before considering focal laser or vitrectomy
- Risk of nausea, rare allergic reaction
OCT Angiography (OCTA)
- Non-invasive vascular imaging — no dye
- Visualizes capillary networks layer by layer
- Identifies the foveal avascular zone enlargement and ischemia
Treatment
Anti-VEGF Injections
| Agent | Brand | Typical Use |
|---|---|---|
| Aflibercept | Eylea | First-line in many centers, especially with worse baseline vision |
| Ranibizumab | Lucentis | Effective, well-studied |
| Bevacizumab | Avastin (off-label) | Lower cost, similar efficacy in milder DME |
| Faricimab | Vabysmo | Dual VEGF and Ang-2 inhibition; extended dosing intervals |
| Brolucizumab | Beovu | Extended interval; inflammation signal noted in trials |
DRCR.net Protocol T (NEJM 2015) compared aflibercept, ranibizumab, and bevacizumab and found aflibercept superior when baseline visual acuity was 20/50 or worse; all three were similar at better baseline vision. Subsequent trials of faricimab and brolucizumab demonstrated comparable efficacy with potential for longer dosing intervals.
Steroid Implants
- Dexamethasone implant (Ozurdex) — lasts 3 to 6 months
- Fluocinolone implant (Iluvien) — lasts up to 3 years
- Second-line when anti-VEGF response inadequate or for pseudophakic eyes
- Risk of cataract and intraocular pressure rise
Focal / Grid Laser Photocoagulation
- Targets leaking microaneurysms outside the fovea
- Largely replaced by anti-VEGF for center-involved DME
- Still useful adjunct for persistent non-center-involved disease
Vitrectomy
- Considered for tractional component or persistent vitreomacular interface disease
- Less commonly first-line in modern era
Systemic Management
- Glycemic control — target A1C as individualized; avoid rapid drops in long-standing poor control
- Blood pressure under 140/90 mmHg, often lower
- Lipid control — statins or fenofibrate reduce DME progression in some trials
- Kidney disease management
- Smoking cessation
- See our overview of treatment strategies for diabetes
Follow-Up
| Phase | Visit Frequency |
|---|---|
| Loading anti-VEGF (months 1 to 6) | Monthly |
| Treat and extend | Every 4 to 16 weeks based on OCT |
| Stable, off treatment | Every 3 to 6 months |
| Annual screening (no DME) | Yearly dilated exam |
Prognosis
- About 50 to 60 percent of treated eyes gain 5 letters or more of vision
- Roughly 30 percent gain 15 letters or more
- Less than 5 percent lose 15 letters
- Persistence is common — many require chronic therapy
- Earlier treatment yields better outcomes than waiting for worse vision
Prevention
- Annual dilated eye exam — at diagnosis for type 2, after 5 years for type 1
- Glycemic control to slow the underlying retinopathy
- Blood pressure and lipid control
- Pregnancy planning with retinopathy assessment beforehand
- Address kidney disease early
- Smoking cessation
- Prompt evaluation of any new vision change — see our complications and related conditions hub for the wider picture
The Bottom Line
Diabetic macular edema is leakage of fluid into the central retina from diabetic capillaries — the most common cause of vision loss in working-age diabetics. OCT is the standard diagnostic tool, and anti-VEGF injections (aflibercept, ranibizumab, bevacizumab, faricimab, brolucizumab) are first-line treatment, supported by the DRCR.net trials. Steroid implants and laser are second-line options. Systemic management of glucose, blood pressure, and lipids is the foundation that limits both the development and the progression of DME. Anyone with diabetes and new or worsening vision should see an eye doctor promptly. Talk to your doctor and seek emergency care for sudden vision loss, floaters with flashes, or curtain-like shadows.
