Recently I came across an interview female astronaut Karen Nyberg gave to CNN. I was struck by some remarks concerning long term vision problems astronauts are having.
KN: This week we've been doing a lot of experiments on our ocular health. We've noticed some problems over the past several years with many of our astronauts.
They come back to Earth after three to six months in space and have long term vision problems, changes in their vision. We are trying to figure out what exactly is causing that.
Luca (Parmitano) and I have been involved in numerous tests. We're doing tonometry -- we are looking at the pressure of the eye. We are doing ultrasounds to look at the morphology of the eye, we are doing fundoscopy to take images of the retina, vision tests.
We are hoping that we can determine exactly what is causing this and hopefully mitigate the problem, especially if we start longer duration missions going to Mars ... we really need to understand this so we don't degrade the vision of every astronaut that is going into space.
I have a theory. After an extended period without gravity the brain adapts to the new situation. So when coming back to earth the vestibular system, which is intricately linked to the visual system, isn't used to gravity anymore. Vision doesn't happen in the eyes, it happens in the brain. The long term vision problems experienced after their prolonged stay in space can be resolved by aiding the brain to readjust to gravity through Vision Therapy.
As a matter of fact, some vision therapy procedures exploit the relationship between balance and vision. Every one of my sessions includes walking over a beam using, each in turn, 4 different kind of prism glasses. This creates a totally new situation for my vestibulo-ocular system to which I am forced to adjust while balancing. It's a good exercise to create some flexibility in the visual system and readjust it's relationship to the vestibular system.
Other exercises combine visual tasks while jumping on a trampoline or using a bongo board.