A class of drugs used for three decades by people infected with the virus that causes AIDS may be effective in treating a leading cause of blindness among the elderly.

HIV drugs called nucleoside reverse transcriptase inhibitors (NRTIs), including AZT and three others, blocked age-related macular degeneration in mice and worked well in experiments involving human retinal cells in the laboratory, researchers said Thursday.

In HIV-infected people, NRTIs block an enzyme the virus uses to create more copies of itself. The new research shows the drugs also block the activity of a biological pathway responsible for activating inflammatory processes in the body.

It is that previously unrecognized quality that makes NRTIs promising for treating macular degeneration as well as graft-versus-host disease, a rarer ailment that can occur after a stem cell or bone marrow transplant, the researchers said.

University of Kentucky ophthalmologist Dr. Jaya-krishna Ambati, who led the study, published in the journal Science, said macular degeneration affects an estimated 50 million people worldwide.

Macular degeneration causes cells to die in the macula, a part of the eye located near the center of the retina that permits vision in fine detail.