Diabetic macular edema: when do we inject, when do we monitor, and how often is treatment needed?

A patient with diabetes comes for a check-up because reading has become harder, or because letters look faded, as if covered by a thin layer of mist. After the examination and the scan, they hear a sentence that worries them: "You have fluid on the macula." Questions follow: Does this mean I will lose my sight? Do I definitely need injections? How many? Can I just be monitored? The answer differs from one patient to another, and in this article we explain why, and how the decision is made.

What does "fluid on the macula" mean?

The macula is a small area in the center of the retina responsible for fine vision: reading, recognizing faces and seeing detail. After years of raised blood sugar, the walls of the tiny blood vessels in the retina weaken and start leaking fluid into the tissue of the macula. The macula swells, like a sponge soaking up water. This swelling is called diabetic macular edema.

It is one of the main causes of poor vision in people with diabetes. In a large review of population studies from around the world, clinically significant macular edema was found in about 4 in every 100 people with diabetes (Teo et al., 2021). It can occur at any stage of diabetic retinopathy, even before advanced changes appear in the rest of the retina.

How do we diagnose it, and why is the OCT scan essential?

Diagnosis starts with examining the retina with the pupil dilated. But the most important tool is optical coherence tomography (OCT), a quick light-based scan that does not touch the eye. It gives a cross-sectional image of the layers of the retina, measures the thickness of the macula precisely, and shows where fluid has collected. OCT has become the main reference for assessing macular edema and following its response to treatment, because it measures it objectively rather than relying on the examiner's impression alone (Virgili et al., 2015).

The most important question we answer on the scan is: has the fluid reached the very center of the macula, or is it still at its edges? Edema that involves the center itself is usually what threatens fine vision, and it drives much of the treatment decision. Sometimes we also need a dye test of the blood vessels (angiography) to find the source of the leak or to assess areas of poor blood supply in the retina.

Treatment starts outside the eye

Before talking about injections and laser, one fact is firmly established: control of blood sugar and blood pressure reduces the chance of retinopathy appearing and getting worse. A large trial in people with type 1 diabetes showed that tight blood sugar control clearly reduced the risk of retinopathy developing and progressing (Diabetes Control and Complications Trial Research Group, 1993). Blood pressure control also reduced small-vessel complications, including worsening of the retina, in people with type 2 diabetes and high blood pressure (UK Prospective Diabetes Study Group, 1998).

But sugar control alone is usually not enough to treat edema that is already present and affecting vision. It is the foundation that protects the eye in the long term, while treatment inside the eye deals with the current problem.

When do we only monitor, and when do we start treatment?

Not every case of macular edema needs injections straight away. The decision depends on two things: does the edema involve the center? and has it affected visual acuity?

Edema involving the center, with vision still good

This is a common situation, and a large clinical trial studied it in more than 700 patients whose vision was good (20/25, or 6/7.5, or better) despite edema at the center. Patients were divided into three groups: immediate injections, laser, or close monitoring with injections started only if vision dropped. After two years, the proportion who lost some vision was similar in all three groups (about 16–19%) (Baker et al., 2019).

In other words, close monitoring, with treatment started at the first drop in vision, is a reasonable option for this group. The American Academy of Ophthalmology guideline states that deferring treatment in this situation is reasonable until vision is affected (Lim et al., 2025). The key word is "close": in this trial, monitoring was regular, with an OCT scan and a vision test at every visit. Monitoring here is a deliberate medical decision, not neglect.

Edema involving the center, with vision reduced because of it

Here the main treatment is injections into the eye with medicines that block vascular endothelial growth factor (anti-VEGF). These medicines have become the first-line treatment, as the role of laser for center-involving edema has declined (Schmidt-Erfurth et al., 2017). The American guidelines confirm that they are effective for center-involving edema that reduces vision (Lim et al., 2025).

An early trial had shown that injections, with laser at the same time or later, improved vision by an average of about two lines on the eye chart after one year, compared with about half a line with laser alone (Diabetic Retinopathy Clinical Research Network et al., 2010). To learn more about how the injection itself is given, read our article on eye injections.

Edema not involving the center

If the edema is away from the center, focal retinal laser or monitoring may be appropriate. An older large study showed that focal laser reduces the risk of vision loss in clinically significant edema that involves or approaches the center (Early Treatment Diabetic Retinopathy Study Research Group, 1985). The doctor chooses according to where the edema is, its size, and how close it is to the center.

Is one medicine better than the others?

Many patients ask this, especially as the medicines differ in price. A large American trial compared three widely used medicines, and the result was very useful for patients:

• When the drop in vision was mild at the start, there was little difference between the three medicines.
• When vision was poorer (20/50, or 6/15, or worse), the improvement after one year was greater with one of the medicines (aflibercept) (Wells et al., 2015). After two years, it remained better than bevacizumab, while the difference from ranibizumab was no longer clear (Wells et al., 2016).

In the most recent Cochrane review of all comparative trials, no practically important differences in vision after two years were found between the different medicines, although they differed in how much they reduced retinal thickness (Virgili et al., 2023). So the medicine is chosen according to the state of the eye, how reduced vision is, availability, cost, and how the patient responds.

Newer medicines allow longer gaps between injections. In two large trials, faricimab achieved vision results similar to aflibercept, with the possibility of extending the interval between injections up to 16 weeks in some patients, depending on disease activity (Wykoff et al., 2022).

How often will I need injections?

This is one of the most important things to know before starting, because keeping appointments is part of the treatment itself.

In the first year, injections are usually close together: roughly one a month at first, until the fluid dries up or vision stabilizes. Then the injections are spaced out gradually. In the American trial mentioned above, patients needed on average about 15–16 injections over two years, with clearly fewer in the second year than in the first (Wells et al., 2016).

More important than the number is not stopping. When the researchers followed the same patients after five years, the retina had kept its improvement, but vision had declined somewhat during the three years in which regular follow-up became less frequent (Glassman et al., 2020). And in an analysis of more than 40,000 eyes treated outside clinical trials, vision improved less than in the trials, mainly because patients received fewer injections than needed (Mehta et al., 2022).

Steroids inside the eye: when do they have a role?

Diabetic macular edema has an inflammatory component, so steroid preparations placed inside the eye can help, including a small implant that dissolves slowly and releases the medicine over months.

In two large three-year trials, about 22% of patients who received this implant had a large improvement in vision (3 lines or more), compared with about 12% in the group given a sham injection. But cataract appeared or worsened in about two thirds of patients who still had their natural lens, and eye pressure rose in some patients, usually treated with drops (Boyer et al., 2014).

So steroids are usually used when the edema does not respond well enough to injections, or in patients who have already had cataract surgery, for whom cataract is no longer a concern (Schmidt-Erfurth et al., 2017; Diabetic Retinopathy Clinical Research Network et al., 2010). Anyone receiving steroids needs regular checks of eye pressure.

What to expect: a dry retina is one thing, better vision is another

The scan may show that the fluid has dried completely, while vision stays lower than the patient hoped. This is not necessarily a failure. A dry retina is anatomical success, whereas the degree of improvement in vision is a functional result that depends on how long the edema was present before treatment, the state of the macular cells, and any other problems in the eye.

On average, vision improves with regular treatment, and the improvement is usually greater in those who started with poorer vision (Wells et al., 2015). No treatment guarantees that vision will return to what it was, but timely treatment protects many patients from losing more.

These figures come from external studies and are not a promise of any patient's result.

What are the risks of the injections?

Injections into the eye are generally safe, but not risk-free. The most serious complication is infection inside the eye, which is rare: about 1 case in every 1,800 injections in an analysis of many studies (Fileta et al., 2014). Other, less serious effects include mild redness at the injection site, or a feeling of something in the eye for a day or two.

Questions patients often ask

Does macular edema mean I will lose my sight?

No, not necessarily. Many patients keep their vision, or their vision improves, with regular treatment and follow-up (Wells et al., 2015). The real danger is neglecting treatment or stopping it.

Can I stop the injections?

Yes. In many patients the injections are gradually spaced out, and they may stop if the condition stabilizes. But the edema can come back, so follow-up with scans continues even after stopping (Glassman et al., 2020).

Can controlling my sugar replace the injections?

Controlling blood sugar and blood pressure protects the retina in the long term (Diabetes Control and Complications Trial Research Group, 1993; UK Prospective Diabetes Study Group, 1998), but it usually does not treat edema that is already present and affecting vision. The two complement each other.

I also have a cataract. Should I have the operation first?

This needs planning, because cataract surgery can increase macular edema in some people with diabetes. So it is usually better to control the edema before the operation. We explain this in detail in our article on cataract surgery in diabetes.

Summary

Diabetic macular edema is one of the main causes of poor vision in people with diabetes, but its treatments have advanced more than almost any other eye condition in recent years. Not every case needs injections immediately: edema that has not affected vision may be monitored closely, edema that has reduced vision is usually treated with injections, and steroids and laser still have a role in particular cases. In every case, control of blood sugar and blood pressure and keeping to follow-up are what protect vision in the long term. We discuss with each patient the option that suits their case, so that their decision is based on a clear understanding of what treatment can achieve.

This information is for health education and does not replace a medical examination.