Eyesight is a very important factor in spaceflight. As the vestibular system is altered in microgravity, visual cues become dominant. The ability to read panels and instruction is critical to the success of a mission. Just recently, though, it has been discovered that spaceflight may cause permanent visual damage. Nearly half of the astronauts returning from the International Space Station suffer from intracranial pressure that can cause optic damage. This pressure arises within the fluid surrounding the brain, working its way down to the optic nerve and the back of the eyeball. Some have recovered from this damage, others have not. The impact has been seen to be more prevalent in men than women.
The causes behind this newly-discovered problem are still being researched, but researchers have already dubbed this new medical issue VIIP or Visual Impairment/Intracranial Pressure. It is speculated by some that the reason various individuals do not suffer vision loss is due to a variation in the internal jugular vein that allows continued blood flow. Men would suffer from optic damage more simply because they typically have thicker sternocleidomastoid muscles, which causes more pressure in this area. Overall, a wide variety of speculations have been made about this phenomenon.
With nutritional deficiencies ruled out, researchers have begun considering the possibility that polymorphisms, which may be part of the one-carbon pathway, could be the cause of vision loss in the astronaut population.
The fact that folate and metabolite variances were seen in the affected astronauts in preflight assessments has lent itself to a variety of theories. These individuals may be more prone to fluid shifts caused by micro-gravity. They may be negatively affected by slight changes in the spacecraft carbon dioxide levels, which are slightly higher relative to those on Earth– a factor that could cause intracranial pressure. But, other astronauts exposed to higher carbon dioxide levels did not have vision changes, weakening this possibility.
Thus, a variety of individualized factors could make certain astronauts more susceptible to intracranial pressure-induced vision loss. This is an obvious connection to the world of Astro-Omics and personalized medicine.
Currently, there are few countermeasures beyond monitoring, and research. Again, artificial gravity would be an applicable solution, likely lessening intracranial pressure. In addition, such research will shift into the realm of Astro-Omics, as we have seen certain individuals to be at higher risk for optic damage. Future research will need to identify possible risk factors, and assess possible individualized countermeasures.