If you were eyeing a $200,000 Virgin Galactic ticket to the stars, you might want to read on. A new study from the University of Texas suggests that astronauts who spend more than 30 days in a weightless, outer-space environment encounter serious ocular problems. Here's what you should know:

How does outer space affect the human body?
Researchers already know that spending long periods of time in a zero-gravity environment — such as that inside the International Space Station (ISS) — results in loss of bone density and damage to the body's muscles. That's partly why stays aboard the ISS are capped at six months. And now, a number of NASA astronauts are reporting that their 20/20 vision faded after spending time in space, with many needing glasses once they returned to Earth.

What did researchers who examined the space-eyesight connection conclude?
The new study, published in the Journal of Radiology, examined the eyes and brains of 27 astronauts who had spent an average of 108 days in space. MRI scans showed that spending just 30 days in space resulted in a rare medical condition called intracranial hypertension — where "pressure inside the skull rises and presses on the brain and backs of the eyes," says Ian Sample at Britain's Guardian.

What kind of damage does that do?
For seven astronauts, intracranial hypertension flattened the backs of their eyeballs, resulting in more long-sightedness. In the case of four astronauts, the optic nerve, which transmits information between the eye's retina and the brain, was enlarged. It's not just eyesight that's affected: Three of the astronauts experienced pressure-related changes to the brain's pituitary gland, which manages a number of the body's functions, including the secretion of growth hormones. 

What does this mean for space travel?
Long-duration space travel, like a months-long mission to Mars, may be facing another "potential limitation," says study lead author Larry Kramer. For its part, NASA says these findings are inconclusive, though it has vowed to study the space-eyesight connection in the future.

Sources: ABC News, BBC News, Fox News, Guardian