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Laser Photocoagulation
Until the year 2000, the only available treatment for the more aggressive, wet form of AMD was laser photocoagulation. In keeping with study recommendations and guidelines, however, this treatment was only applicable in 13% to 26% of patients with wet AMD (as defined by MPS criteria) and marked by significant limitations17; ideally, it was used only in those patients with small, well-defined lesions located outside the fovea and, when possible, outside the macula.18
Laser photocoagulation uses a thermal (heat-producing) laser beam to cauterize abnormal blood vessels in the retina. In doing so, however, it damages the retina since, before this beam can cauterize the vessels, it must penetrate the RPE, destroying any healthy tissue in the overlying retina and causing an abnormal scotoma to form over the treated area.17 For the remaining 80% to 90% of patients whose neovascularization presents subfoveally, the benefits of thermal laser treatment must be weighed against the certainty, immediacy, and permanency of vision loss.
Photodynamic Therapy With Visudyne
The treatment options available for wet AMD changed dramatically in the year 2000 when the FDA approved Visudyne therapy in the United States for patients with predominantly classic subfoveal CNV secondary to wet AMD. As a result of this approval, more patients are now able to be treated for vision loss associated with wet AMD than in the past. Visudyne therapy selectively closes CNV, halting the progression and size of CNV lesions while slowing the loss of and, in some cases, preserving visual acuity. In 2001, the FDA also approved Visudyne for the treatment of pathologic myopia and presumed ocular histoplasmosis.
Visudyne therapy involves an intravenous injection of Visudyne (verteporfin for injection), a photosensitizer, or light-activated drug. After infusion, Visudyne is selectively activated by illuminating a light from a non-thermal laser source at a wavelength (689 nm) that corresponds to the absorption peak of the drug. The power of the laser is not strong enough to cause any thermal damage to the retinal tissue.
Visudyne is a potent second-generation photosensitizer derived from porphyrin. The molecule has a long absorption wavelength with several peaks, including a strong absorption peak in the 688 to 692 nm region.19 Visudyne efficiently absorbs light at wavelengths around 690 nm (red light), which can penetrate blood, melanin, and fibrotic tissue.20 To learn more about Laser Activation With Visudyne, click here.
How It Works
Once inside the bloodstream, Visudyne (viz-yoo-dín) is transported in the plasma primarily by lipoproteins.
When Visudyne is activated by light in the presence of oxygen, highly reactive, short-lived singlet oxygen and reactive oxygen radicals are generated. Light activation of Visudyne results in local damage to neovascular endothelium, resulting in vessel occlusion. Damaged endothelium is known to release procoagulant and vasoactive factors through the lipo-oxygenase (leukotriene) and cyclo-oxygenase (eicosanoids such as thromboxane) pathways, resulting in platelet aggregation, fibrin clot formation and vasoconstriction. Visudyne appears to somewhat preferentially accumulate in neovasculature, including choroidal neovasculature. However, animal models indicate that the drug is also present in the retina. Upon photoactivation, then, Visudyne therapy may cause collateral damage to surrounding tissue or adjacent retinal structures, such as the overlying photoreceptors and RPE. The temporary occlusion of choroidal neovascularization (CNV) following Visudyne therapy has been confirmed in humans by fluorescein angiography.
Treatment
Studies show that a full course of Visudyne therapy can help reduce the risk of moderate and severe vision loss in patients with subfoveal CNV.1 In all cases, patients receiving Visudyne must be prepared to commit to a full course of therapy with the goal of stopping CNV leakage completely.
In addition, Visudyne has a well-established safety profile, with more than 5 years of clinical experience and more than 700,000 patient treatments since being approved. Click here to learn more.
For more information on Visudyne efficacy, click here.
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