Traveling in space has many odd effects on the human body. One of the strangest has to do with vision.
After spending some time on the International Space Station, many astronauts discover that they cannot see as well as they do on Earth. The effect is so well known that members of the crew routinely pack “space glasses” to correct their vision in orbit.
Researchers still aren’t sure
Lack of gravity causes a shift in bodily fluids to the head. This puts pressure on the eyes and optic nerve, making vision blurry. So may astronauts wear glasses.
But a trip to Mars will be so long that we simply do not yet know what the long term effects on vision will be. It kind of makes travel moot if the astronauts end up blind.
Image: NASA on The Commons