Macular edema is a fairly common disease of the retina, which affects its central part, the macula, and can lead to severe loss of visual acuity. Its causes are multiple and guide the treatment, effective if the disease is not too advanced. 

Definition

Macular edema is a condition characterized by thickening of the central part of the retina, called the macula, due to fluid infiltration causing an inflammatory reaction. 

The macula is a small area of ​​the retina measuring about 1 mm that is very rich in visual cells, which is responsible for precision vision. When it is very close to the center of the retina and threatens visual function, it is called clinically significant macular edema. Left untreated, it can lead to severe permanent central visual acuity loss.

Macular edema is sometimes called cystoid macular edema to indicate that the accumulation of fluid occurs in small cavities (stalls) like cysts.

Depending on the cause, edema may affect only one eye, for example after surgery, or both (bilateral edema).

Causes and risk factors

The appearance of macular edema is linked to a small loss of fluid from the blood vessels that supply the retina, generally following alterations that have modified the permeability of their wall. 

The causes of edema are multiple, edema can take different forms depending on the conditions of its formation:

• It is often the consequence of a complication of diabetes, diabetic retinopathy, in which chronic excess sugar ends up weakening the wall of blood capillaries.
• Other common causes, venous obstructions are responsible for dilation of the veins of the retina, itself the cause of edema.
• Uveitis, intraocular inflammatory pathologies, can also cause macular edema, which will then have a strong inflammatory component.
• Surgery, especially cataract surgery, can also be involved.
• Other associated disorders: AMD (age-related macular degeneration), arterial hypertension, eye tumor, retinitis, genetic disorders, etc.

Diagnostic

The diagnosis of macular edema can call for various examinations.

• The thickening of the retina in the area of ​​the macula can be observed during an ophthalmologic examination of the fundus, carried out with a biomicroscope, also called a slit lamp.
• Optical coherence tomography (OCT), a non-invasive imaging test used in ophthalmology since the early 2000s, is the gold standard. It cuts the macula and makes it possible to highlight its morphology and to measure its thickness.
• Angiography (radiological examination of the vessels) makes it possible to visualize and photograph abnormalities in blood vessels and fluid leaks after injection of a dye, fluorescein. More rarely, ICG angiography (in infrared light) will be performed, which shows different details after injection of indocyanine green.

The people concerned

Macular edema is a very common pathology due to its association with common pathologies.

• It is the main cause of low vision in diabetic patients. After 20 years of development, it would concern at least 30% of them. However, its frequency seems to be falling in industrialized countries thanks to better diabetes control.
• Each year, more than 20 cases of macular edema appear in France following venous occlusion.
• It is estimated that a quarter of people with uveitis have reduced vision associated with macular edema.
• Transient macular edema is very common after eye surgery. Twelve months after cataract surgery, the frequency of persistent cases is around 3%.

Macular edema at the start of its development is generally painless, with very discreet symptoms: slightly cloudy vision, defects in color perception, etc.

Its progression leads to a more or less pronounced impairment of visual function.

Central vision loss

The decline in visual acuity is often gradual, causing difficulty in distinguishing details. This loss of central vision is a handicap for all tasks that require precise visual control, such as reading or writing. It can lead to low vision and blindness

Scotome

A deficit in the central visual field called scotoma may be associated with edema. A blind spot appears at the fixation point.

Visual distortions

Macular edema also sometimes causes distortions (ripples) in straight lines called metamorphopsis, which may be accompanied by a micropsy, which makes objects appear smaller than they actually are.

The therapeutic approach should be tailored depending on the cause of the macular edema, the degree of severity, the patient’s history and side effects.

Pharmacological treatments

• Anti-inflammatories

Corticosteroids administered locally as eye drops, ointment or injection or systemically (oral or intravenous) are used for their powerful anti-edematous and anti-inflammatory action, but can have significant side effects (glaucoma, cataracts, etc.). NSAIDs can also have their place in treatment.

• Anti-angiogéniques

The discovery of a growth factor called VEGF (vascular endothelial growth factor) involved in numerous retinal vascular pathologies has paved the way for new treatments. In recent years, anti-VEGF molecules belonging to the therapeutic class of anti-angiogenic drugs, administered by injection into the eye (intra-vitreous injection) have demonstrated their efficacy and good tolerance in the treatment of macular edema.

New anti-angiogenic treatments are currently under development.

• Other pharmacological treatments

Other classes of molecules have more limited indications, such as carbonic anhydrase inhibitors, or ACIs (eye drops, oral) used in the treatment of certain edemas of non-vascular origin, or even immunosuppressants and anti- TNF-α, useful in certain forms of inflammatory macular edema refractory to corticosteroids.

Photocoagulation au laser

This physical treatment uses laser pulses to clot leaky or abnormal vessels. It is not always easy to implement and presents risks of thermal damage in the eye, but the advent of more sophisticated lasers, with shorter pulse durations (micropulse lasers), or coupled with imaging has improved its safety and efficiency.

Surgical treatment

In rare cases, surgical strategies are possible.

There is no specific prevention for macular edema. However, its onset in diabetics can be prevented or delayed by good diabetes control, ensuring blood sugar levels within the norms. 

In addition, in people at risk, periodic ophthalmological checks will promote early detection of edema and the initiation of treatment before the damage becomes irreversible.

The pathologies causing macular edema must be treated to avoid recurrence.