What is Choroidal neovascularization (CNV)?

What is Choroidal neovascularization (CNV)?

Introduction

Choroidal neovascularization (CNV) is the major cause of severe visual loss in patients with age-related macular degeneration (AMD). Choroidal neovascularization is a pathologic condition characterized by the abnormal formation of new blood vessels in the choroid—the vascular layer of the eye between the retina and sclera. Its primary function is to provide nourishment to and eliminate metabolic waste from the outer layers of the retina.

Who is at risk of Choroidal neovascularization?

Smoking: Smokers are at significant higher risk for developing AMD and, hence, CNV. There was also little reduction in risk even 15 years after a person quits smoking.

Other risk factors include high blood pressure, possibly high blood sugar in diabetes, elevated cholesterol and obesity (especially in men). It also seems that the very leanest are at some increased risk as well.

What causes Choroidal neovascularization?

Typically, CNV is seen in a number of ocular diseases, especially Adult Macular Degeneration (AMD), Pathologic Myopia (PM) and Ocular Histoplasmosis Syndrome (OHS). However, any condition where there is a disruption in Bruch’s membrane, can lead to a compromise of the choroid’s primary functions and lead to increased risk for development of CNV.

How does Choroidal neovascularization develop?

Choroidal neovascularization occurs when new blood vessels originating in the choroid (the innermost layer of the eye which contains almost all of the blood vessels) begin to grow through a break in the Bruch membrane (the inside layer of the choroid) into the sub-retinal space. Ocular neovascularization is known to grow with the presence of excess levels of vascular endothelial growth factor (VEGF), and is counteracted by a protein produced by the retinal epithelia called pigment epithelium derived factor (PEDF). The balance between these two proteins is believed to be the main determining factor in whether and how rapidly CNV progresses.

Will I go blind if I get Choroidal Neovascularization?

Choroidal neovascularization is a leading cause of blindness in the western world. It causes 90% of the visual loss in age-related macular degeneration. If left untreated, CNV can cause a rapid deterioration in central vision and color recognition. During the disease progress, new blood vessels grow from the choroid and penetrate through the bruch membrane into the subretinal pigment epithelial and subretinal space. These vessels can leak and bleed, leading to exudative retinal detachment and hemorrhage. Eventually, this process progresses to a fibrovascular scar with destruction of photoreceptors and vision loss (blindness).

How do I know if I have Choroidal neovascularization (Signs & symptoms)?

Commonly observed signs and symptoms of CNV include:

  • Sudden deterioration of central vision, noticeable within a few weeks
  • Metamorphopsia, and colour disturbances
  • Hemorrhaging (bleeding) of the new blood vessels

Can Choroidal neovascularization be cured?

Until recently, the most common treatment of leakage from neovascular lesions was laser photocoagulation. However, only about 15 to 20 percent of patients with leakage are candidates for this treatment. In this procedure, the laser energy is converted from coherent light to heat in the choroid. This essentially “spot welds” the lesion, destroying the abnormal leaking blood vessels. However, this treatment causes full-thickness retinal damage and, in the case of subfoveal lesions, leads to immediate loss of central vision. In an attempt to provide more selective and effective treatment for CNV in neovascular AMD, several innovative therapies have been studied, including photodynamic therapy (PDT) and agents that target new blood vessels growth. The goal of these treatments is to effectively treatCNVwithout damaging adjacent retinal tissue. A number of other new treatments (radiotherapy, systemic thalidomide and other antiangiogenic agents, macular translocation, submacular membrane excision) are under investigation

PDT (photodynamic therapy)

In PDT, a photosensitizing drug is injected intravenously and activated by a non-thermal laser light in affected vessels in the retina. Using the appropriate drug dose, light dose, and timing of irradiation, relatively selective occlusion of CNV vessels can be achieved with minimal effect on the retina.

Drug injection therapy

Most recently, the FDA approved ranibizumab injection therapy, trade name Lucentis™, as a treatment for neovascular AMD. Lucentis™ is another VEGF inhibitor administered through 6 intravitreal injection. Like other VGEF inhibitors, this drug binds to receptor binding sites, preventing interaction of VEGF-A with its receptors on the surface of endothelial cells. This action reduces cell proliferation and neovascularization.

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