美国国家公共电台 NPR Doctor Launches Vision Quest To Help Astronauts' Eyeballs（在线收听）

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You would expect a trip into space would change a person - their heart, their soul, but their eyeballs? For years, a north Texas doctor has been trying to find out what causes this vision change among astronauts. Her latest research may provide some clues. Lauren Silverman from member station KERA in Dallas reports.

LAUREN SILVERMAN, BYLINE: After spending six months on the International Space Station, Michael Barratt had a strange request when he finally stepped foot on Earth. He wanted a spinal tap.

MICHAEL BARRATT: Yep, it ranked right up there with a hot shower.

SILVERMAN: Barratt isn't a masochist. He's a NASA astronaut who, while flying hundreds of miles above the Earth in 2009, noticed his vision was changing. He was struggling to read checklists.

BARRATT: When you're reading in Russian, in small print, in a dark place and your visual acuity starts to tank, I mean, you notice it (laughter).

SILVERMAN: Barratt is also a curious physician, which brings us back to his request for a spinal tap to check the pressure in his brain. He knew he wasn't the first astronaut whose vision had changed while in space. And he hoped sticking a needle into his back might provide a clue to his vision loss. The theory - micro-gravity raises pressure in the head and reshapes the eyeballs.

BARRATT: This is a medical issue that affects a large percentage of people who fly in space and for which we are now making very expensive mission decisions - how we're going to go to Mars and whatnot - so the stakes are extremely high.

SILVERMAN: Scientists know that when people go into space, the fluid normally below their hearts goes into their heads. But is it creating enough pressure to damage the eyes, to squish them and affect the optic nerve? Dr. Benjamin Levine has been on a mission to find out at UT Southwestern Medical Center and Texas Health Resources in Dallas. Instead of sticking needles in astronauts' backs, though, he wanted to stick them inside people's brains.

BENJAMIN LEVINE: Basically - and that's what we did. We didn't actually do the drilling, but we found people who'd had holes put in their brain.

SILVERMAN: Levine found eight healthy cancer survivors who already had ports in their heads - once used to deliver chemotherapy. Then he convinced them to get on a plane for a sort of extreme rollercoaster ride to simulate zero gravity.

UNIDENTIFIED MAN #1: (Unintelligible).

SILVERMAN: You know that feeling of weightlessness when you drop on a roller coaster?

UNIDENTIFIED MAN #2: Woo.

SILVERMAN: Well, these folks did that except they plunged 8,000 feet in 30 seconds, dozens of times, all in the name of science.

TRENT BARTON: I enjoyed each and every rotation that we did.

SILVERMAN: Trent Barton, a lymphoma survivor from Dallas, went on the wild trip above the Texas-Mexico border. Here he is talking during the car ride after the flight.

BARTON: And that was a lot gadgets on me. I had things hooked up to both arms. This blood pressure on my finger that was literally tracking blood in and out of my finger.

SILVERMAN: Most importantly, he had a needle in that port in his head monitoring the pressure in the fluid surrounding his brain. Remember, they're testing the hypothesis that pressure inside the brain at zero gravity is so high it damages the eyes and...

LEVINE: The main idea is wrong.

SILVERMAN: Turns out, Levine says, spaceflight doesn't cause pressure to be that much higher than it is when you or I are standing up. But it is a little higher. The research is published in The Journal of Physiology.

LEVINE: We now think that perhaps this mild but persistent pressure may be the thing that's stimulating remodeling behind the eye and causing the visual impairment.

SILVERMAN: See, unlike us earthlings, astronauts never get to rest their brains in lower pressure. When they're standing up, the fluid won't go to their feet. So researchers like Levine are now trying to find a way to give these astronauts' brains a rest.

LEVINE: We've been working with Under Armour, the garment company, to come up with a soft, almost like a sleeping sack or a pair of trousers, that you can put on at night, hook up to a vacuum cleaner, suck the blood and the fluid into the feet and unload the heart and the brain while you're sleeping.

SILVERMAN: Astronaut and doctor Mike Barratt says he'd be willing to try the sleeping sack, but he also wants to do more tests on the International Space Station to better understand intracranial pressure, especially before we send astronauts deeper into space. As for his eyesight six years post-fight...

BARRATT: It's my right eye that has apparently been permanently remodeled. Other than that, I'm totally normal.

SILVERMAN: He's still the same curious doctor. He just sees things a bit differently since returning to Earth. For NPR, I'm Lauren Silverman in Dallas.