Neovascular membranes

Neovascular membranes (NVM) are due to abnormal growth of blood vessels from the capillaries of the choroid (the vascular layer that supplies blood and feeds the retina) that grow until they break through the retina, the subretinal space in particular. These vessels are very immature and tremendously fragile, so they bleed and leak, destructuring the macula (the central region of the retina) and producing significant visual damage.

NMV are painless although they are accompanied by severe visual symptoms. At the start of the disease, however, it is not uncommon for the patient to be asymptomatic , especially if only one eye is affected. 

In general, patients visit the doctor because their vision has quickly become blurred, making it difficult to read and write, estimate distances and depths, the size of objects and perception of colours, in addition to other symptoms. 

Furthermore, the appearance of metamorphopsia (perception of distored images and straight lines with curves) including the inability to recoginse faces, drive, sew, etc... 

As the disease progresses, it causes a central black spot (scotoma), the size of which varies depending on its stage of progression. We must highlight that peripheral vision is usually preserved in the majority of cases, which is why patients retain a certain amount of autonomy and independence in daily tasks that do not require much precision.

NVM are more common in people over the age of 50 and the risk increases with age, as the most common cause is wet or exudative age-related macular degeneration (exudative AMD).

Another group of patients inclined to suffer from NVM are short-sighed people, in which case they are called myopic neovascular membranes.

The onset of NVM is also common in diseases that cause a rupture of the Bruch membrane (the innermost layer of the choroid) as this facilitates the proliferation of anomalous vessels towards the retina, in this case the traumatic choroidal ruptures or after laser surgery and in patients with angioid streaks. Inflammatory diseases of the choroid and the retina like toxoplasmosis, histoplasmosis, multifocal choroiditis and other disease may become complicated with NVM.

Cases in which we find NVM but no apparent cause after a meticulous ophthalmic study are called idiopathic NVM (i.e. of an unknown cause).

There are different categories depending on their:

• Cause (as mentioned above) 
• Location with respect to the macula (subfoveal – just below the macula, juxtafoveal – near the macula, and extrafoveal – far from the macula)
• Angiographic appearance – whether they are classic or hidden and mixed association. como clásicas u ocultas y mixtas. It is currently a defunct category, however, the fluoroscein angiography (FA) is not. It continues to be the diagnostic technique of choice. This test involves the injection of a fluorescent dye into a vein in the arm and taking photographs of the back of the eye. The dye helps to show the lesions as they are vascular structures that capture the dye intensely.

The onset of NVM cannot be prevented as they are associated with other basic conditions (myopia magna, uveitis, etc) and, more commonly, the natural and irreversible process of ageing, as is the case with exudative age-related macular degeneration (AMD).

What is advisable, however, is a regular eye check-up and "self-monitoring at home" for those with a family history of NVM. These are performed using an Amsler grid, a test that is easy to do and involves a square with vertical and hortizontal lines, which, should they appear curved or have spots, act as warning to the patient that they should see a doctor as soon as possible. 

The treatment currently indicated for these lesions, no matter what the cause, are intravitreal injection of antiangiogenic agents. These act by limiting the growth of pathologic blood vessels, which slows, and in some cases stops, the disease, preserving or even improving vision.