Last Friday, March 27, NASA and Roscosmos sent two astronauts for a one-year space mission. The aim of this expedition is to investigate how being in space for such a long time can affect the human body and behaviour. Consequences of space flight environment in human physiology and psychology are already known, from common half-year missions. The point is to understand if these consequences are aggravated by a longer journey, as for a travel to Mars which would last about three years. According to the National Space Biomedical Research Institute, some of the body reactions to lack of gravity include loss of calcium in bones, loss of muscles mass (especially those used for posture), redistribution of fluids throughout the body, and changes in the balance system. Scientists are particularly interested in the effects of such environment in vision, since some astronauts have been reporting vision impairment, namely degradation of near vision, during and after space missions.
As a review by Marshall-Bowman and colleagues suggests, the causes of this vision deterioration are not yet fully understood, but they have been hypothesized to be based on the redistribution of body fluids. In a microgravity environment fluids are not pulled down by gravity and a greater amount is distributed in the upper body, including the head. Consequently, intracranial pressure increases, affecting the optic nerve, which swells due to difficult venous circulation. The eyeball becomes flatter, and shorter, leading to the hyperopic vision reported by the long-duration astronauts. However, the influence of other factors must be evaluated, like higher levels of carbon dioxide, the duration of the vision impairment after the space mission, and individual predisposition. This new expedition will be important to better understand these effects, also considering that one of the astronauts has a twin who will serve as a “Earth- control” to evaluate his brother’s body changes.