Portland, Ore. ? In what may be an important step toward preventing blindness in old age, scientists have identified a gene believed to be responsible for a degenerative eye disease that could strike millions of baby boomers as they grow older.

The gene is suspected of being the main cause of some cases of age-related macular degeneration, or AMD, a complex disease triggered by various factors. It typically affects people 65 and older.

Researchers at Oregon Health & Science University were able to pinpoint the gene by tracking it through a large extended family with a history of the disease.

“We were really lucky to get a single family that large with 10 affected members,” said Dennis Schultz, an Oregon Health & Science University biochemist who led the research at the university’s Casey Eye Institute.

In age-related macular degeneration, the most sensitive area of the retina breaks down, robbing a person of the fine vision needed to read a book or recognize a face. In severe cases, it can lead to almost total blindness.

About 6 million Americans suffer from AMD, a number that is predicted to double by the year 2030 as the baby boomer generation ages. There are treatments for the disease, but the goal is prevention.

Dr. Johanna Seddon, a Harvard researcher, said more studies would have to be done to establish whether the gene is the single source of some cases of AMD. If the gene proves to be the source, it is possible gene therapy could be used to delay or even prevent the disease, she said.

“But I think that’s still quite a way off,” Seddon said.

The study was published Tuesday in the online version of the journal Human Molecular Genetics and will appear in print in the December issue.

Genes that play a role in forms of macular degeneration that affect younger people have been identified. But this is the first solid evidence of a genetic cause for the age-related form, researchers said.

But doctors warn there are many other factors that contribute to age-related macular degeneration, including other genes, as well as environmental factors, such as smoking.