Choroidal neovascular membrane (CNVM) is a problem that is related to a wide variety of retinal diseases, but is most commonly linked to age-related macular degeneration. With CNVM, abnormal blood vessels stemming from the choroid (the blood vessel-rich tissue layer just beneath the retina) grow up through the retinal layers. Imagine the abnormal blood vessels as weeds creeping up through the cracks of a pavement. These new vessels are very fragile and break easily, causing blood and fluid to pool within the layers of the retina.
As the vessels leak, they disturb the delicate retinal tissue, causing the vision to deteriorate. The severity of the symptoms depends on the size of the CNVM and its proximity to the macula. Patients' symptoms may be very mild such as a blurry or distorted area of vision, or more severe, like a central blind spot.
A simple vision test called an Amsler Grid should always be done first for patients who notice a problem with their central vision. This test provides the eye care practitioner with vital information about the location and severity of the problem. CNVM is usually difficult to diagnose by simply looking at the retina with an ophthalmoscope. A special dye test called a fluorescein angiogram is used to study the circulation of the retina and show areas of leaking blood vessels.
The appropriate treatment is dependent on several factors such as: size and location of the membrane and the amount of time that passed since the symptoms first began. If the CNVM is small, compact, and caught very early, a delicate surgery called a
sub-foveal excision can be performed to remove it. This procedure has the most risk but also offers the patient the best possibility of visual improvement.
Laser photocoagulation, a procedure that seals leaking blood vessels, is the simplest and most common treatment for CNVM. It is reserved for patients with bleeding outside of the central retina because it creates a scar that affects the vision. Treating the retina with laser gives the surgeon the most control over placement and size of the scar. Allowing an undiagnosed leak to resolve on its own usually causes a much more devastating affect on the vision.
Unfortunately, for some patients, no treatment is appropriate. All patients with CNVM should monitor their vision with an Amsler Grid and report any changes to their eye care practitioner immediately.
Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.