Brain scans revealed that seven of the 27 astronauts had a flattening of the back of one or both eyes. By making the eyeball shorter, this made the astronauts more long-sighted, which in some cases had the effect of reducing or correcting their short-sightedness…

“There are major political, social and individual ramifications relative to this thought alone,” Dr Kramer said. “Consider the possible impact on proposed manned missions to Mars or even the concept of space tourism. Can risks be eventually mitigated? Can abnormalities detected be completely reversed? The next step is confirming the findings, defining causation and working towards a solution based on solid evidence.”

Four of the astronauts had swelling around the optic nerve, which could affect the transmission of signals from the eye to the brain and, in the longer term, cause nerve fibres to die off. Three of the astronauts had slightly deformed pituitary glands, though this was not thought to be harmful.