As the collective consciousness of the dreamy-eyed wanderers fantasizes about hurtling humans toward the red planet, we may need to think abiout things that are not necessarily addressed in books and films like The Martian.
Spaceflight-Associated Neuro-Ocular Syndrome (SANS) is an eye problem, or perhaps more correctly a constellation of eye problems, related to long duration space flight. This is currently poorly understood, but some of the problems include decreased ability to see up close, swelling of the optic nerve, and wrinkles/folds of the back of the eye.
What are the long term consequences of SANS, and how long does “long duration” space flight have to be to induce them? We don’t yet seem to have good answers to these questions, but it is definitely worth figuring out before people embark for other planets.