These new blood vessels often lack integrity and leak blood and fluid that harm the central retina the damage to the retina causes eventual scarring and drastic vision loss over time.ĪMD Trials Treatment of AMD with Photodynamic Therapy (TAP) The wet form of AMD is characterized by the rapid growth of abnormal choroidal neovascular blood vessels under the macula. Indications Age Related Macular Degeneration (Neovascular)
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Fifteen minutes after intravenous infusion, low power laser is applied (standard dose of 50 J/cm 2, irradiance of 600 mW/cm 2 of 689 nm light over 83 seconds ) which activates the phototoxic Visudyne to seal leaking blood vessels by generating these free radicals in areas of necessary treatment. After injected into the bloodstream, the Visudyne(6 mg/m 2 dose) selectively collects in the abnormal blood vessels in the retina and choroid. In the case of neovascularization, this process serves to induce regression of these harmful blood vessels.
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The anti-inflammatory response can lead to series of events including vasoconstriction, thrombosis, increased vascular permeability, blood stasis and hypoxia. The reaction that ensues between the free radicals and blood vessel endothelial cell membranes cause locally increased histamines, thromboxane and TNF-α, all immune modulation factors. Photodynamic therapy with verteporfin causes release of free radicals when the verteporfin is activated by the laser energy. Verteporfin has been approved for the treatment of wet AMD since 1999 by the USFDA, having undergone Phase III clinical trials. Moreover, Verteporfin can be rapidly cleared from the body, minimizing patient photosensitivity to 1 to 2 days. Verteporfin was the second generation photosensitizer developed to treat wet AMD with an intensified long-wavelength absorption maxima at approximately 690 nm, compared to the first generation photosensitizer Photofrin with a weaker wavelength absorption (630 nm), indicating a 50% increase in tissue penetration by light. Verteporfin (marketed as Visudyne), also known as benzoporphyrin derivative, is commonly used as a photosensitizer in Photodynamic Therapy, with a molar mass of 718.794 g and a half-life of 5 to 6 hours.
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