How Can VEGF Affect My Vision?
What is neovascularization?
These are new vessels originating from and contiguous with the pre-existing retinal vascular bed. They are located either within or adjacent to the retina, in areas where vessels are not normally present. Neovascularization occurs as a result of some stimulus, the nature of which is not known, provoking pre-existing retinal vessels to proliferate abnormally. The stimulus appears to be related to situations involving poor retinal nutrition resulting in retinal hypoxia and/or the accumulation of metabolic products.
Where does VEGF come from, and why?
Vascular endothelial growth factor (VEGF) is a naturally-occurring protein in the body responsible for growing blood vessels to replace damaged or dying ones. It does this by stimulating endothelial cells. VEGF is a multi-tasking protein which stimulates differentiation, survival, migration, proliferation and vascular permeability in endothelial cells.
Here, it should be worth mentioning that VEGF has been connected to several eye diseases including certain forms of macular degeneration, neovascular glaucoma, and diabetic macular edema. Therefore it is logical to ask what makes this, otherwise normal productive protein, a potentially harmful one especially with respect to the eye. It must be noted that the microcirculatory problems in the retina of people with diabetes can cause retinal ischemia (deficient oxygen supply) which results in the release of VEGF and a switch in the normal balance of VEGF over the normally present VEGF which may then cause the creation of new blood vessels in the retina and elsewhere in the eye, heralding changes that may threaten the sight.
Will I definitely have trouble with VEGF if I am diabetic?
No. The good news is that until and unless your diabetes is chronic (long term) and / or is poorly controlled, chances are that the normalized blood sugar levels will not cause “abnormal” release of VEGF. Hence, even if you’re diabetic, you will not necessarily develop diabetic nephropathy and retinal damage due to the VEGF. It must be remembered that high blood sugars cause damage to individual cells and later shows up as damage to structures like capillaries, the smallest of blood vessels. Endothelial cells, which form a very smooth surface on the inner walls of blood vessels, are especially damaged by excess sugar. As damage progresses, the blood vessel walls starts to become porous, letting proteins and other materials leak out abnormally and causing VEGF release.
What are endothelial cells, why are they important & how they are linked with the eye?
The endothelium is the biological active inner layer of the blood vessels, which serves as an important locus of control of vascular and thus organ functions. It is mainly composed of endothelial cells. These endothelial cells form the walls of blood vessels and exchange oxygen and nutrients with tissue waste. The back part of the eye is covered in endothelial cells around the retina. When oxygen is depleted to the endothelial cells because of ischemia, or lack of oxygen supply, VEGF goes to work to produce new cell walls and blood vessels to replace the damaged ones by a process known as neovascularization. Unfortunately, where this process works very well in other parts of the body, it does now work at all inside the eye, and the newly-created blood vessels are improperly formed, causing blood leakage. This causes scarring of the macula, finally resulting in a lack of central vision.
Types of treatments & medicines used
Following types of treatment and medicines are frequently used to correct or prevent the progression of diabetic nephropathy caused due to the involvement of VEGF:
Anti-VEGF drugs: Treatment with Avastin (bevacizumab) and Lucentis (ranibizumab) known as anti VEGF drugs, which are also used to treat cancer helps maintain vision, is a common practice. Avastin and Lucentis are anti VEGF (vascular endothelial growth factor) drugs AND they block the action of VEGF proteins that form new blood vessels in response to oxygen deprived cells.
Avastin and Lucentis are given intravitreally, through the sclera, the white part of the eye, using a very small needle, after the eye is numbed with topical drops. Clinical practices vary, but Anti VEGF drugs are usually administered over a period of time of 1 to 2 years, starting with monthly dosing. It must be noted that anti VEGF drugs are not a cure for macular degeneration. Damage already done before treatment begins may be irreversible. According to the Merck Manual, approximately one third of patients will see improvement in their vision. Some patients will have vision loss slowed or stopped.
Anti-diabetic drugs: VEGF is also suppressed or blocked by a newer class of specific anti-diabetic drugs known as thiazolidinediones (used for diabetes mellitus type 2 and related disease).
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