3 VEGF is known to stimulate and mediate vasculogenesis, endothelial cell migration and tube formation. When photoreceptors and neurons are deprived of oxygen and nutrients that are usually supplied by healthy vessels, the resultant hypoxia triggers VEGF release. While normally present in healthy eyes, VEGF is highly expressed in proliferative disease, triggering the growth of neovascularization. 1 In the retina, disease processes that cause damage to normal retinal vasculature, leading to ischemia and retinal nonperfusion, typically stimulate the growth of neovascularization.Ī key contributor that has been heavily studied in this process is vascular endothelial growth factor (VEGF). For example, wound repair in the skin involves the formation of new blood vessels to compensate for those that have been damaged. Neovascularization is a protective mechanism that many tissues throughout the body have in response to injury. Severe neovascularization with hemorrhage and fibrous proliferation in diabetic retinopathy, leading to tractional retinal detachment. In either case, these new vessels invade areas where vessels are not normally present. 1 These two distinct blood supplies are separated by the retinal pigmented epithelium.īecause of this dual supply, neovascularization in proliferative disease processes can arise either from the primary inner vasculature- termed retinal neovascularization-or the vasculature in the choroid, called choroidal (or subretinal) neovascularization. By contrast, the outer one third of the retina is supplied by the choroidal vasculature. 1 This system is made up of deep and superficial capillary beds that are responsible for nourishing the inner two thirds of the retina. The vasculature of the inner retina is located far enough anteriorly to the photoreceptors that light is able to navigate around it. Instead, the entire retina is nourished by a dual blood supply: blood vessels within the inner retinal layers and the choroid. Because of this, the outer retina is largely avascular, as blood vessels would prohibit image formation if located immediately in front of the photoreceptors. As we already know, for vision to occur, light needs to reach the photoreceptors. In order to understand their mechanisms, it is first necessary to distinguish normal retinal angiogenesis and blood supply. Proliferative retinal diseases are generally classified as either causing retinal or choroidal neovascularization. As such, understanding how and why they arise is crucial. It is important that the eyecare practitioner be able to accurately identify these treatable proliferative processes as early as possible. As complications can be severe, more effective therapeutic solutions are continuously being evaluated. However, in order to do so, timely diagnosis and management is vital. Many treatments are aimed at reversing these conditions and preserving visual function. Proliferative retinal diseases are one of the leading causes of vision loss worldwide.
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