Angiogenesis is the process by which the body grows new blood vessels. In healthy adults, normal angiogenesis occurs in healing wounds and during reproduction, but in all other situations, it is abnormal.
Exudative AMD is caused by abnormal angiogenesis. New vessels grow under the macula and disrupt the central region of the retina. These new blood vessels bleed and leak fluid, causing the macula to bulge or lift up from its normally flat position and impair central vision. If left untreated, scar tissue can form and central vision is irreversibly lost.
The process of angiogenesis has been studied by researchers for more than 40 years. Here’s how it happens:

• New blood vessels are stimulated to grow by special proteins called “growth factors”.
• One protein called Vascular Endothelial Growth Factor (VEGF) is made in high amounts in the retina of people with wet AMD.
• Excess VEGF causes new blood vessels to sprout from pre-existing blood vessels under the macula.
• The new, sprouting blood vessels that grow because of the excess VEGF are very fragile and leak fluid, causing edema, and may bleed.
• New vessels form loops.
• Special cells called pericytes are recruited to the newly forming blood vessels, and these pericytes wrap around the vessels to stabilize their structure.
• Other cells called “endothelial progenitor cells” are also recruited to the new vessels. These are special stem cells that normally reside in the bone marrow but respond to signals from growing blood vessels.