June 3, 1997
Media Contact: Marc Kusinitz
"Our success so far is particularly exciting because there's no other treatment as effective for the wet form of age-related macular degeneration."
A new laser technique first developed to treat throat cancer also may stop vision loss caused by a blinding eye disease, according to preliminary studies led by a Johns Hopkins researcher. The procedure, called photodynamic therapy, appears to prevent further loss of sight in people already suffering from the "wet" form of age-related macular degeneration. The wet form of age-related macular degeneration occurs when abnormal blood vessels grow within the retina, the light-sensitive part of the eye. Damage caused by fluid leaking from these vessels and scar tissue robs people of their central vision.
More than a million people in the United States and Canada have the disease, and about 200,000 new cases are diagnosed in those countries each year, according to Neil M. Bressler, M.D., associate professor of ophthalmology. Bressler is chairing the multicenter trials under way to further test photodynamic therapy in people with the wet form of age-related macular degeneration. The current therapy uses heat from a standard, "hot" laser to destroy some vessels. But the treatment may fail to stop regrowth, Bressler says. More importantly, these lasers often damage healthy parts of the retina as well. This means these lasers can be used only in a minority of cases in which the abnormal blood vessels are small.
"Our preliminary success in treating over 100 patients in Phase I and Phase II trials is particularly exciting because there's no other treatment for most people with this form of age-related macular degeneration," Bressler says. "An added advantage may be that it can be repeated over the course of several months if necessary without injuring the retina."
Results of the study were presented at the annual meeting of the Association for Research in Vision and Ophthalmology in Fort Lauderdale, Fla. in May.
Done on an outpatient basis, the laser treatment takes advantage of the presence of fat-carrying molecules in rapidly growing tissues. The first step includes injecting a drug called BPD-MA--or verteporfrin--into a vein.
During the next ten minutes, the drug is picked up by molecules in the blood called lipoproteins. Lipoproteins are a source of cholesterol and are taken up specifically by the rapidly growing abnormal blood vessels in the retina.
In the second step, 15 minutes after the injection, the physician shines a beam of red laser light into the eye. The red light contains no heat but does activate the BPD-MA attached to the lipoproteins swept up by the blood vessels. The activated BPD-MA produces a toxic form of oxygen that causes partial or complete absence of leakage from the abnormal blood vessels. This may confine the growth of the scar tissue and prevent further vision loss, according to Bressler.
Researchers in the United States, Canada and Europe are now recruiting 540 patients for a two-year study.
BPD-MA was developed by QLT PhotoTherapeutics Inc. (Vancouver, British Columbia), and the study is supported by QLT and CIBA Vision Ophthalmics Inc. (Duluth, Ga.).