Space travel is awesome, and sometimes the astronauts that go to space enjoy the experience so much that they really don't want to come back to the boring physics here on Earth. On the other hand, there are some drawbacks to long-term space travel.
One of those problems is vision impairment, which seems to be a common issue for astronauts that spend extended periods of time in space. Now, NASA seems to have an explanation for why this occurs.
As time is spent in space, an astronaut's cerebrospinal fluid, which is the fluid that protects the brain and spinal cord, can multiply in volume, which is generally a good thing in space, but probably isn't so when the astronauts come back to Earth.
All that fluid has to go somewhere, and once an astronaut comes back to Earth, physics tend to push that extra volume towards the eyes, which may flatten the back of the eyeball, changing the shape of the retina and impacting a long-term astronaut's vision in the process.
All that said, if you plan on being an astronaut and spending long periods of time in space, you might expect to have vision problems later on in life...