News that long-term space travel can risk causing damage to vision may dampen enthusiasm for future trips.

The University of Texas Medical School in Houston has run MRI scans on 27 astronauts who’ve been on either the International Space Station (pictured), a NASA shuttle, or both.

The scans found that:

• with nine astronauts, the cerebospinal fluid space around the optic nerve had expanded;
• six had flattening at the back of the eyeball;
• in four cases, the optic nerve itself has bulged; and
• three astronauts had experienced changes in both the connection between the pituitary gland and the brain, and in the gland itself (though not to the extent of causing physical harm).

It appears any effects usually wear away after a few weeks back on Earth.

The symptoms are all reminiscent of a condition known as idiopathic intracranial hypertension (IIH) , which means there is pressure around the brain without an obvious medical cause such as a tumor. As well as leading to headaches and nausea, the condition can cause visual problems and, if untreated, eventually to vision loss.

Nasa has recorded vision changes with some astronauts, but hasn’t yet found cases where it has been so severe that it has affected their ability to travel or work in space. Medical staff will now take a closer examination of whether IIH may be the cause and has added vision damage to its list of potential human risks in space travel that need to be studied and monitored.

While the sample group for the study, led by Dr Larry Kramer, was inevitably small, there are at least indications of a link between the time spent in space (specifically in zero or low gravity) and the likelihood and extent of vision damage. That could be problematic for manned missions to Mars that would take at least twice as long as a stay on the International Space Station.

The Guardian notes that bodily fluid is known to move in the direction of the head in space when gravity is no longer a factor, “giving astronauts puffed-up faces and scrawny legs.” It may be that space travel leads to excess production of cerebospinal fluid that is unable to escape through the skull and thus puts pressure on the back of the eyeballs.