Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries and affects 40% of people over the age of 75. It is caused by a slow degeneration of the pigment layer under the retina. This pigment layer, the retinal pigment epithelium, is essential for normal function of the retina.
Amongst its many important functions it helps regenerate the visual pigments required for the retinal photoreceptors to function. After several years, changes become visible within the central part of the retina, the macula. This is the part of the retina that is responsible for central vision which is necessary for reading, writing, driving and recognizing peoples’ faces. These early changes are termed atrophic or ‘dry’ AMD and cause a very slow deterioration in central vision. Dry AMD is the least severe type of AMD. There is no treatment for atrophic AMD.
Photodynamic therapy is a form of treatment for the “wet” or exudative form of age-related macular degeneration. As described elsewhere on our website, the “wet” form of macular degeneration involves the growth of abnormal blood vessels called choroidal neovascularization (CNV), beneath the retina resulting in leakage and bleeding (see figure below). Without treatment, a majority of patients eventually develop scar tissue beneath the macula (the central part of the retina), which results in loss of central vision. In some cases, the blood vessels causing the leakage and bleeding are located outside the central part of vision. If these blood vessels are imaged by techniques known as fluorescein angiography, laser treatment can be applied, and vision stabilized or improved in a small number of people. Unfortunately, only 15-20% of people, are eligible for treatment in this manner. Even if laser treatment is possible, more than half of the patients receiving laser therapy eventually develop regrowth of the blood vessels, and eventual central visual loss.
Given the poor prognosis for treatment with the “wet” form of macular degeneration (see drawing), new and investigational techniques have been attempted in order to stabilize or improve the visual outcome in these patients. Over the last several years, techniques such as radiation therapy and surgical removal of the abnormal blood vessels have been attempted, but studies have not yet proven any benefit of these techniques. In some cases, these treatments may lead to a worse outcome than would be expected if the eye had been left alone.
Encouragingly, there are several ongoing investigational trials using medications which have the potential to slow down or halt the progression of these abnormal blood vessels and lead to a better vision outcome. All of these studies, however, are investigational, and no proven benefit of any medical therapy for this disease has yet been shown. As soon as data becomes available for these other investigational techniques, I will attempt to add them to this website.
A new and exciting research development in the treatment of wet macular degeneration is the technique known as photodynamic therapy.
In order to understand this treatment approach, it is important to remember that the difficulty with the “wet” form of macular degeneration is the growth of abnormal blood vessels beneath the retina which leak fluid and bleed. The fluid and blood cause scar formation which leads to damaged vision. The concept of photodynamic therapy is to selectively close the abnormal blood vessels, eliminating the leakage and bleeding, and stabilizing or improving the vision. This is done without the damaging effect of conventional laser on the normal structures of the retina and back of the eye.
Photodynamic therapy is a two step process.
- In the first step, a patient receives an injection of a special dye called Visudyne (liposomal BPD-MA verteporfin) through a vein in the hand or arm. This dye has unique properties which allow it to be used for this treatment. Specifically, this chemical circulates through the body and sticks to the walls of the abnormal blood vessels beneath the macula.
- At this point in the procedure, a laser is used to shine a light into the back of the eye. The energy produced by this laser is of a very low power and is not damaging like regular laser treatment. Instead, the light simply activates the chemical which is bound to the abnormal blood vessel wall. When the chemical is activated by this light beam, there is closure of the blood vessel. The end result is that the fluid and blood which had been leaking beneath the retina is stopped. Over time, the body is able to absorb the blood and fluid, which results in stabilization or improvement in visual function. The blood vessel itself has not been completely destroyed, but rather is no longer leaking nor actively growing.
After receiving photodynamic therapy with Visudyne, the dye remains within the body for approximately 24 hours. As a result, patients are required to avoid exposure to sunlight, and intense halogen lights for a period of 24 hours until the drug has completely cleared out of the body.
In spite of the fact that these blood vessels may lie directly beneath the center of vision, photodynamic therapy does not result in damage to the normal retinal tissue or to the wall of the eye. As a result, unlike in traditional laser treatment, vessels directly beneath the center of vision can be effectively treated and closed without causing permanent damage to vision. Some patients may experience temporary visual changes associated with the treatment, but vision usually returns within a matter of days.
Over the course of 1-3 months, the blood vessels that have been treated with the photodynamic technique typically open again and leakage may recur. Treatment is performed at three month intervals, if there is evidence of continued leakage from the blood vessels. In spite of the need for multiple treatments (every three months), stability of vision and resolution of leakage can be achieved in many patients.
Since the publication of the one year data, analysis of two year results from the Visudyne therapy trials has confirmed the long term benefits of this treatment. Specifically, it has been found that patients continue to experience stabilization in vision, throughout the two year follow-up period. In addition, approximately 13% of patients do experience a significant degree of vision improvement at the two year point. In April 2000, the Food & Drug Administration, the government agency responsible for regulating all forms of medical treatment in the United States, approved Visudyne therapy for patients with choroidal neovascularization secondary to age-related macular degeneration. Patients with specific types of neovascularization as determined by fluorescein angiographic evaluation are now eligible for treatment with this very exciting therapy. It should be kept in mind that not all patients benefit from the treatment, and the decision regarding an individual’s potential benefit from this therapy should be made by their eye care provider in conjunction with a qualified retinal specialist.
It is important to keep in mind that photodynamic therapy is not for everyone. In spite of the fact that this does represent a breakthrough in treatment for “wet” macular degeneration, not all individuals are eligible for therapy. In particular, the results of the clinical trial just completed on Visudyne therapy are only applicable to those individuals with a particular type of abnormal blood vessel under the retina, and for blood vessels which are of a certain size and have certain features on examination. Your eye care provider will be able to determine if you are a candidate for treatment under these guidelines. In addition, it is very important to realize that this therapy does not restore vision in eyes that have already been significantly damaged by age-related macular degeneration. If an individual already has advanced scarring of the macula or extensive damage due to blood and chronic fluid leakage, this therapy is not likely to result in an improvement in the visual function. More often, instead, this treatment will be most effective for those patients with new leakage and relatively good vision.
Given the positive results from the Visudyne study, it is likely that photodynamic therapy will come to play a significant role in the treatment of patients with the “wet” form of macular degeneration in the near future. With the development of other techniques, including medications and perhaps other forms of therapy, we hope to have a better approach to the management of patients with this disease, including for those in which photodynamic therapy is not an option.
Please note: Much of the above content was provided compliments of: Vitreous-Retina-Macular Consultants New York