The reason appears to relate to subtle changes to bodily fluids, where prolonged exposure in zero-gravity leads to physiological changes taking place. The research findings have been reported in a conference paper, titled “Role of Cerebrospinal Fluid in Spaceflight-Induced Visual Impairment and Ocular Changes.”
It has been known for a while, website Mental Floss summarizes, that a prolonged time in orbit can shrink astronauts’ hearts and stretch their spines; it also affects their vision. This is noted with astronauts returning to the Earth needing glasses to read or to drive after being back on terra firma for a short period of time.
The reason, following an in-depth study of eight astronauts (who agreed to undergo extensive medical tests), is due to a condition called visual impairment intracranial pressure. Here increased pressure inside astronauts’ heads affects the structure of the eye and the ability to focus unaided. Specifically, the optic nerves of astronauts show more swelling that would occur on Earth, and the alterations are irreversible. The findings have been reported to the annual meeting of the Radiological Society of North America.
Such results are important if humans are ever to embark on deep space missions, such as reaching Mars, and to do so while remaining relatively healthy. In light of this, Digital Journal reported earlier that an instrument aboard the spaceship that carried Curiosity to Mars has found that deep space travelers would face worrying levels of radiation. These health concerns need to be considered along with the more obvious technological issues of space craft design and fuel consumption.
