Recently, a study showed that changes found in astronauts' eye tissue might cause vision problems, and possibly even blindness. As well as threatening the health of astronauts, this could influence long-distance missions into space. Larry Kramer of Texas Medical School in Houston and his colleagues carried out MRI scans on 27 NASA astronauts after they had spent an average of 108 days in space. About half of them had some problems in their optic nerve   or eyeball. The changes match those seen in people with idiopathic intracranial hypertension, a rare condition in which the pressure of blood is abnormally high in the brain. People with the condition experience headaches, nausea   and vision problems including blindness. In space, the changes are probably caused by living in free fall. "It is not because of the sunlight in space or the spacecraft's function," says Kramer. "One likely reason is that blood which normally pools in the legs is shifted toward the skull  , raising pressure."  The findings are similar to the results of a survey of 300 astronauts carried out in 2011. The damage in vision was reported by 29 percent of astronauts on short-term missions, and 60 percent on long-term missions. "If astronauts are exhibiting these changes after only 100 days in space, what will happen on a three-year flight to Mars?" asks Jason Kring, who studies human performance in extreme conditions at the Embry-Riddle Aeronautical University in Florida. "Deteriorating vision could seriously damage astronauts' ability to carry out routine mission tasks, including monitoring displays and navigating the rocky landscape of Mars," says Kring. "This possibility, combined with what we already know about how micro-gravity affects muscles and bones, paints a dark future for human space flight unless we start to develop effective measures." Kramer says that NASA has the matter in hand. In the wake of the study, all astronauts now have regular brain scans. This includes those yet to travel into space, providing a baseline   from which any changes would be obvious. He also believes it might be possible to identify astronauts' risk of eyesight damage from medical data before sending them into space. What can be inferred from the passage?
Staying for a long time in space will lead to blindness. Scientists' research in space will be banned soon. Space flight makes astronauts' bones function better. NASA has started to care for astronauts' eyesight.