WASHINGTON (AP) — An experimental drug is showing promise against an untreatable eye disease that blinds older adults — and intriguingly, it seems to work in patients who carry a particular gene flaw that fuels the damage to their vision.

Age-related macular degeneration, or AMD, is the leading cause of vision loss among seniors, gradually eroding crucial central vision. There are different forms but more than 5 million people worldwide, and a million in the U.S., have an advanced type of so-called "dry" macular degeneration that has no treatment. First patients may notice blurriness when they...