THE MOST COMMON CAUSE OF BLINDNESS IN PEOPLE MORE than 50 years old is age-related macular degeneration. The disease afflicts 7 million people in North America alone. At the onset, a mesh of abnormal blood vessels spreads across the retina, eventually creating scar tissue and obscuring vision. Surgeons today burn away the new growth with lasers, but that damages normal eye tissue as well.
Scientists working for Quadra Logic Technologies Inc. in Vancouver, B.C., and CIBA-Vision Corp. in Duluth, Ga., hope to avoid such side effects with a technique called photodynamic therapy (PDT). The idea is to inject patients with light-sensitive dyes that concentrate naturally in new blood vessels. When irradiated with low-powered lasers, the dye molecules release oxygen atoms that attack and kill the host cell membrane. In tests at Harvard University on diseased primate eyes, the method cleared away new blood vessels without hurting older, functional blood vessels.
Quadra Logic already uses photodynamic therapy to kill tumors in the esophagus and other organs. That procedure is permitted in Canada, Japan, and Holland, and it may soon be approved by the Food & Drug Administration for use on tumors in the U.S. Early test data suggest the therapy may also be effective for skin diseases such as psoriasis. Meanwhile, Quadra and CIBA are asking the FDA for permission to begin human clinical trials for eye treatments in early 1995.