Question: How can you become blind from spaceflight?

Adrianos Golemis answered on 26 Jan 2016:

We are not sure yet, as eyesight problems because of spaceflight is a relatively new issue. However, no one has become blind so far, some Astronauts have merely returned home with less keen eyesight. This could be because in space there is no gravity and thus all the liquids in your body tend to accumulate in the upper part, including the head – in this way liquid also gathers behind your eye and might slightly harm the optical nerve. It is all still under investigation, though.