Lylas G. Mogk, MD, a renowned expert on age-related macular degeneration (AMD), founding director of the Visual Rehabilitation and Research Center of Michigan, part of the Henry Ford Health System Eye Care Services, and co-author of Macular Degeneration: The Complete Guide to Saving and Maximizing Your Sight [1], explains:
"In wet AMD, the choroid (a part of the eye containing blood vessels that nourish the retina) begins to sprout abnormal blood vessels that develop into a cluster under the macula. This process is known as choroidal neovascularization, or CNV.
Because these new blood vessels are abnormal, they tend to break, bleed, and leak fluid under the macula, causing it to lift up and pull away from its base, damaging the fragile photoreceptor cells, which sense and receive light. This can result in a rapid and severe loss of central vision.
Unlike dry AMD, however, a range of treatments currently exist for wet AMD, including the use of anti-angiogenic drugs, photodynamic therapy, macular translocation surgery, and thermal laser photocoagulation."
The study of anti-angiogenic drugs has received considerable attention in ophthalmology and cancer research and is an exciting and promising development in the treatment of wet AMD.
Angiogenesis is a term used to describe the growth of new blood vessels and plays a crucial role in the normal development of body organs and tissue. Sometimes, however, excessive and abnormal blood vessel development can occur in diseases such as cancer (tumor growth) and AMD (retinal and macular bleeding).
Substances that stop the growth of these excessive blood vessels are called anti-angiogenic (anti=against; angio=vessel; genic=development), and anti-neovascular (anti=against; neo=new; vascular=blood vessels).
The focus of current anti-angiogenic drug treatments for wet AMD is to reduce the level of a particular protein (vascular endothelial growth factor [2], or VEGF) that stimulates abnormal blood vessel growth in the retina and macula; thus, these drugs are classified as anti-VEGF treatments.
At present, these drugs are administered by injection directly into the eye after the surface has been numbed. The needle is very small and is inserted near the corner of the eye — not the center. During the injection procedure, the doctor will ask the patient to look in the opposite direction to expose the injection site, which also allows the patient to avoid seeing the needle.
The following anti-angiogenic/anti-VEGF drugs are currently in use to treat wet AMD:
Macugen was approved for AMD treatment by the U.S. Food and Drug Administration (FDA) in December 2004 and is administered once every six weeks. You can learn more about Macugen on the Macugen web site: About Macugen [3].
Lucentis was approved for AMD treatment by the FDA in June 2006 and is administered on a schedule determined by your ophthalmologist. Additional clinical trials are underway to determine the optimal dosing schedule. You can learn more about this drug on the Lucentis web site: What Is Lucentis? [4]
Avastin is an anti-VEGF drug that is FDA-approved for intravenous use in colorectal cancer. It is currently used on an "off-label" basis (i.e., via eye injection) to treat wet AMD.
In October 2010, researchers at Boston University School of Medicine and the Veterans' Administration Boston Healthcare System released clinical trial results indicating that Avastin is as effective as Lucentis for the treatment of wet AMD. You can read more about the clinical trial results at Avastin and Lucentis are equally effective in clinical trial for treatment of wet macular degeneration [5] on the VisionAware blog.
In April, 2011, preliminary results from the highly anticipated Comparison of Age-Related Macular Degeneration (AMD) Treatments Trials (CATT) that tested the effectiveness of Avastin (bevacizumab) versus Lucentis (ranibizumab) in a head-to-head clinical trial indicated that Avastin is as effective as Lucentis for the treatment of wet AMD. You can read more about the clinical trial results at Avastin vs. Lucentis for AMD: Preliminary Research Results [6] on the VisionAware blog.
In June, 2011, the United States Food and Drug Administration (FDA) announced that its Advisory Committee is reviewing Regeneron Pharmaceutical's application for the AMD drug VEGF Trap-Eye. You can read more about VEGF Trap-Eye clinical trial results at VEGF Trap-Eye: A Potential New Treatment for Macular Degeneration [7] on the VisionAware blog.
Photodynamic therapy (PDT) [8] was developed by researchers at the Massachusetts Eye and Ear Infirmary and has been approved for AMD treatment by the FDA since April 2000. PDT works as follows: A 10-minute intravenous administration of Visudyne [9] (a photosensitive drug) is followed by the application of a low-dose, non-thermal (light only) laser to the affected area of the retina. The drug circulates throughout the body's blood vessels, and is particularly attracted to new blood vessels, including the abnormal vessels under the macula.
The laser activates the drug, which selectively seals off the leaking blood vessels without damaging the surrounding healthy retinal tissue. This feature allows PDT to be used directly beneath the center of the macula, unlike thermal (heat) laser photocoagulation, which can burn and destroy normal retinal tissue.
Macular translocation [10] is a surgery that involves detaching the retina from its base, rotating it slightly, and replacing it in a different position, so that the macula sits on a new, healthy base. While macular translocation surgery is unlikely to become standard treatment for everyone with wet AMD, it has proven effective for some when done promptly. It does not work for dry AMD because, for reasons not yet understood, the degeneration recurs in the new position.
Thermal laser photocoagulation is a technique used by retinal surgeons to treat a number of eye conditions, one of which is wet AMD. A thermal (heat) laser is directed into the eye at abnormal blood vessels growing beneath the retina. The heat from the laser closes off the unwanted blood vessels, preventing further leakage and vision loss.
Thermal laser photocoagulation does not restore lost vision; therefore, in the past, it was critical that treatment be initiated as early as possible in the course of the disease. Unlike PDT, however, thermal laser can also destroy surrounding healthy retinal tissue as it seals the leakage from abnormal blood vessel growth; therefore, it is not used on vessels directly under the center of the macula. At present, thermal laser is rarely used in clinical practice.
Treatments differ for the wet and dry types of macular degeneration, and new research is ongoing. Learn more about new clinical research on treatments for macular degeneration by listening to a lecture on "Macular Degeneration: Stepping into the New Decade" [11] given at the American Foundation for the Blind Center on Vision Loss in Dallas by ophthalmologist, Robert Witherspoon, M.D.
Links:
[1] http://www.amazon.com/Macular-Degeneration-Complete-Saving-Maximizing/dp/0345457110/sr=1-1/qid=1169131927/ref=pd_bbs_sr_1/105-7367909-6963648?ie=UTF8&s=books
[2] http://www.mdsupport.org/library/anti-angio.html
[3] http://www.macugen.com
[4] http://www.lucentis.com
[5] http://visionaware.blogspot.com/2010/10/avastin-and-lucentis-equally-effective.html
[6] http://visionaware.blogspot.com/2011/05/avastin-vs-lucentis-for-amd-preliminary.html
[7] http://visionaware.blogspot.com/2011/06/vegf-trap-eye-potential-new-treatment.html
[8] http://www.mdsupport.org/library/photther.html
[9] http://www.visudyne.com/
[10] http://www.mdsupport.org/library/mactrans.html
[11] http://www.afb.org/seniorsite.asp?SectionID=63&TopicID=286&SubTopicID=227