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*!\
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Since then, astronauts aboard Skylab, the Shuttle, Mir, and the
International Space Station have all reported seeing these flashes. No
need to call the *Men in Black*, though: what the astronauts are
experiencing is space radiation. Like subatomic bullets, cosmic rays zip
through the eyes of astronauts. 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 lenses in their eyes.

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 (see journal references below). 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.\
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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? It\'s a mystery.

Cataracts on Earth are a bit of a mystery, too. The lens of the human
eye becomes cloudy, to a degree, as a natural result of aging. In some
cases it gets too cloudy to see through; cataracts can cause blindness
if left untreated. More than half of people older than 65 have
cataracts, yet no one is sure why the lens changes as we age.

There\'s an intriguing connection here between space travel and aging.
Both lead to cataracts. Understanding one might help with the other.

NASA-supported researcher Eleanor Blakely and colleagues at the Lawrence
Berkeley National Laboratory (LBNL) are working on it. \"We have to
decipher the basic biology,\" she says. How, exactly, does radiation
cause cataracts? \"That\'s what we\'re mapping out at the moment.\"

To understand her research, you must first understand some basic
eye-anatomy:

The lens of the human eye is a small bundle of transparent cells called
fibroblasts. This bundle, about the size of an M&M, sits in the opening
of the eye and focuses incoming light on the retina. Like a chocolate
M&M, which is encased in a thin skin of candy, the lens is encased by a
thin skin of \"epithelial\" cells. These epithelial cells not only
protect but also renew the lens. When needed, they can transform
themselves, flattening out, elongating, and shedding their nucleuses and
other internal structures to become transparent fibroblasts.

Blakely\'s group has shown that a radiation dose can alter the
transformation of eipithelial cells, thus interfering with the formation
of fresh fibroblasts that make up the body of the lens.

They didn\'t deliberately irradiate people\'s eyes to figure this out,
of course. Instead, they cultured human epithelial cells in petri
dishes. As some of the cells were beginning to turn into fibroblasts,
her team exposed the cells to controlled doses of radiation. Afterward,
they used modern genetics tools to find out how the cells\' genes and
proteins responded.\
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They\'ve found that a particular gene, Fibroblast Growth Factor 2
(FGF-2), jumps in activity eight-fold following a radiation dose. FGF-2
normally helps the cells respond to stress. In this case it boosts the
activity of two more genes called \"p21\" and \"p57.\"

These genes, in turn, influence the life cycle of the cell, controlling
crucial events such as when the cell divides to form two daughter cells.
Blakely suspects that an imbalance in p21 and p57 might derail the
normal life cycle of epithelial cells. Fewer fibroblasts are made to
replace old ones. The lens becomes cloudy.

Because the radiation in space is a mixture of various kinds of
high-speed particles and high-energy photons of light, her group did
separate tests using several kinds of radiation. For X-ray and proton
beam exposures, they used on-site facilities at LBNL. But to test the
effects of the most damaging form of space radiation \-- high-speed iron
nuclei produced by supernovas \-- her team had to go to the newly
constructed NASA Space Radiation Laboratory at the Brookhaven National
Laboratory in Long Island, New York.\
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Their research continues at both facilities. Although their discoveries
so far are tantalizing, there\'s more to learn. For instance, they still
need to confirm that the genes they suspect are indeed the culprits.
Blakely also wants to know why cataracts in astronauts appear so many
years after exposure to space radiation. Could sudden big doses of
radiation accelerate the process? Astronauts taking off on a 6-month
trip to Mars will want to know that!

The group recently won a three-year extension of their NASA research
grant. Stay tuned for updates.