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 the eyes
of astronauts 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 that focuses light on 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 (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.\
\
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. Diabetes,
physical injury and certain medications (especially steroids) increase
the risk. More than half of people older than 65 have cataracts, yet
researchers aren\'t sure\--at the genetic or cellular level\--what
causes them.

\"Studying cataracts in astronauts might help unravel the mystery of
cataracts in ordinary people, too,\" says Eleanor Blakely, a scientist
at the Lawrence Berkeley National Laboratory (LBNL). Supported by a NASA
grant, she and her colleagues are investigating what happens to human
eyes when they\'re zapped by space radiation.

\"For good vision, the lens of the eye must be crystal clear,\" says
Blakely. The lens is a small bundle of transparent cells called \"fiber
cells.\" When fiber cells become cloudy, you have cataracts.

In a normal human eye, new fiber cells are constantly manufactured to
replace old ones. They start out as \"epithelial cells,\" a type of stem
cell that coats the front of the lens. When needed, epithelial cells
flatten out and shed their nucleuses and other internal structures to
become transparent fiber cells. It\'s an amazing metamorphosis. \"During
the final stages,\" she says, \"all of the cell\'s organelles are
disposed of by the cell in a carefully orchestrated process that leaves
the cell alive, but basically a bag of crystalline proteins.\"

Blakely\'s group has shown that a radiation dose can upset this
metamorphosis.

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 fiber cells,
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.\
\
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 cells respond to stress. In this case, it appears to have
boosted two other genes called \"p21\" and \"p57.\"  These genes control
crucial events in the life cycle of a cell\--*e.g.,* when a cell divides
to form two daughter cells, or when an epithelial cell transforms into a
fiber cell.

Blakely suspects that an imbalance of p21 and p57 leads to the formation
of abnormal fiber cells and, possibly, the cloudiness of cataracts.

 \
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 \-- her team had to go to the newly constructed NASA Space
Radiation Laboratory at the Brookhaven National Laboratory in Long
Island, New York.\
\
Their research continues at both facilities. Although the discoveries so
far are tantalizing, there\'s more to learn. For instance, says Blakely,
\"we still need to confirm that the changes we saw in genetic activity
\[triggered by radiation\] are linked to the appearance of cataracts
many years later.\" Could sudden big doses of radiation accelerate the
process?  Astronauts taking off on a 6-month trip to Mars will want to
know.\
\
The group recently won a four-year extension of their NASA research
grant. Stay tuned for updates.