Cataracts - Blinding Flashes

Years after exposure to space radiation, many astronauts' vision becomes clouded by cataracts. Understanding why may shed light on cataracts suffered by elderly people.

Gazing out of their space capsules, Apollo astronauts witnessed sights that humans had never before seen. They saw the breathtaking view of the Earth's bright blue disc against the inky black of space. They saw the far side of the Moon. They also saw strange flashes of light inside their eyeballs!

Since then, astronauts aboard Skylab, the Shuttle, Mir, and the International Space Station have all reported seeing these flashes. No need to call Agents Mulder and Scully of The X Files, though: what the astronauts are experiencing is space radiation zipping through their eyes like subatomic bullets. When a "bullet" strikes the retina, it triggers a false signal that the brain interprets as a flash of light.

Needless to say, this is not good for your eyes. Years after returning to Earth, many of these astronauts developed cataracts - a clouding of the lens, which focuses light onto the retina.

At least 39 former astronauts have suffered some form of cataracts after flying in space, according to a 2001 study by Francis Cucinotta of NASA's Johnson Space Center. Of those 39 astronauts, 36 had flown on high-radiation missions such as the Apollo Moon landings. Some cataracts appeared as soon as 4 or 5 years after the mission, but others took 10 or more years to manifest.

Astronaut Joseph Tanner photographed during a 1997 spacewalk.

Scientists have long known of this link between radiation and cataracts, but they've never fully understood it. What exactly does radiation do to the lens of the eye to make it cloudy? Are astronauts' genes involved? Which ones?

Solving this puzzle might help people on Earth. Without ever traveling through space, more than half of people older than 65 get cataracts; cloudy lenses seem to be a natural result of aging. These old-age cataracts, some of them, resemble the cataracts astronauts get. If researchers can figure out what's happening inside astronauts' eyes, they might be able to develop medicines to stop the process.