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According to one NASA survey of about 300 astronauts, nearly 30 percent of those who have flown on space shuttle missions – which usually lasted two weeks -- and 60 percent who've completed six-month shifts aboard the station reported a gradual blurring of eyesight.
Williams put the figure lower -- at roughly 35 percent for station crew -- but did not dispute the severity of the problem, nor the mystery surrounding it. The disorder, similar to an Earth-bound condition called papilledema, is believed to be caused by increased spinal-fluid pressure on the head and eyes due to microgravity, although the exact cause is uncertain.
Oftentimes, the problem goes away once an astronaut returns to Earth. But a recent study by the National Academies noted there had been "some lingering substantial effects on vision," and that astronauts were "not always able to re-qualify for subsequent flights" -- at least not immediately.
Williams declined to discuss specific cases, but acknowledged at least one astronaut never regained normal vision.
"When they [NASA] start going [to] long-distance [destinations] like Mars, you can't end up having a bunch of blind astronauts."
While blindness is the worst-case scenario, the threat of blurred vision is enough that NASA has asked scores of researchers to study the issue and has put special eyeglasses on the space station to help those affected see what they're doing.
Originally posted by Afterthought
reply to post by Grifter81
Well, at first, I wasn't considering that the greys have biology similar to ours since I was assuming that their eyes were constructed similarly to insects' eyes. Think of the preying mantis and how their eyes are.
Now that I've learned that space travel may inhibit eyesight, I'm leaning more towards the idea that the large black eyes aren't eyes at all, but may be large balck lenses designed to protect their eyes or help them see better.
Originally posted by seabhac-rua
, their big bug eyes.....wrap around shadesedit on 20-9-2011 by seabhac-rua because: (no reason given)