What is choroidal neovascularization?
Choroidal neovascularization (CNV) is the growth of abnormal blood vessels in the choroid. The choroid is the blood vessel-filled middle layer of the eye, which lies between the sclera and retina. These abnormal blood vessels can leak fluid and blood, damaging the retina and causing vision loss.
What causes choroidal neovascularization?
The exact mechanism of the development of CNV is not fully understood. It is believed that a protein called vascular endothelial growth factor (VEGF) is released in excess by a thin layer of cells called the retinal pigmented epithelium (RPE).
The RPE is located in the outermost layer of the retina. The retina is the inner light-sensitive tissue in the back of the eye that converts light into signals that are sent to the brain for processing.
VEGF is normally found in the eye and helps to maintain the retina. However, low levels of oxygen, inflammation or other stressors can cause excess production of VEGF by the RPE.
The excess VEGF stimulates the growth of new, abnormal and fragile blood vessels in the choroid. The choroid is a thin layer of blood vessels that helps to maintain the outer layers of the retina, providing oxygen and nutrients and carrying away waste.
Eye anatomy illustration of the Bruch's membrane in the back of the retina
In addition to producing VEGF, the RPE — along with a membrane called Bruch’s membrane — forms a barrier between the choroid and retina. When too much VEGF is produced, abnormal blood vessels form and break through this barrier, leaking fluid and blood into the spaces between the choroid and retina.
This results in injury to the retina, particularly the photoreceptor cells known as rods and cones. These specialized photoreceptor cells are critical to vision because they transform light into electrical signals that the brain processes as images. Damage to the rods and cones leads to vision loss.
READ MORE: Choroid of the eye: Anatomy and function
