All astronauts have perfect eyesight before traveling to outer space, but some years ago medical tests revealed that their vision is severely impaired when they return. The exact cause of this problem is yet to be determined.

In 2005, about halfway through his mission working on the International Space Station, astronaut John Phillips looked out the window at Earth and noticed something strange. Although his vision had always been perfect, our planet seemed blurry and he had problem focusing on it. He didn’t report his problem to ground control thinking it was just temporary and would go away after a while, only it didn’t. When he returned to Earth, rigorous tests revealed that his eyesight had gone from 20/20 to 20/100.

To shed some light on this issue, NASA put Phillips through a series of procedures, including MRIs, retinal scans, neurological tests and a spinal tap. They found that not only had his vision deteriorated, but his eyes had changed as well – his optic nerves were inflamed, the back of his eyes had become flatter and his eyeballs had choroidal folds, which are like stretch marks. After six months, Phillips’ eyesight improved to 20/50, but remained there for the last 11 years. He went from being the guy with the best vision, the first one in the car to read a street sign to not being able to pass a DMV exam without glasses.

Photo: NASA

His was the first confirmed case of a mysterious syndrome that affects about 80 percent of astronauts on long missions in space. It was named Visual Impairment Intracranial Pressure Syndrome (VIIP), after the leading theory to explain it. On Earth, bodily fluids are pulled down towards the feet by gravity, but that doesn’t happen in space, and scientists believe that the extra fluids in the skull increase pressure on the brain and the back of the eye. This theory makes sense, but actually confirming it is an even bigger problem.

The only proven methods of measuring intracranial pressure are the spinal tap or drilling a hole in the back of the skull, both of which are invasive. “There’s the risk for infection and just doing the procedure, quite frankly, in space is difficult,” said J.D. Polk, a senior flight surgeon at NASA. “Having to anchor somebody and do a spinal tap in space is not something we would relish.”

Photo: NASA

However, VIIP could pose a big problem in the advent of a trip to Mars, so scientists are scrambling to learn more about what’s causing it. Karina Marshall-Goebel at the Institute of Aerospace Medicine in Germany is trying a head-down tilt test in which participants’ bodies are tilted slightly to simulate the fluid shift in space, but the test is affected by gravity and they can’t keep people tilted for nearly as long as astronauts live in space. “It’s a unique environment; you can’t replicate it without going into space,” she told the Washington Post.

Others are looking at less invasive ways of accurately reading intracranial pressure, which Eric Bershad, an intensive-care neurologist at the Baylor College of Medicine, says may become viable in the next five years. Ross Ethier, a biomedical engineer at Georgia Tech, is working on a device that could draw fluid back down to the legs in space, but it might prove uncomfortable to use, and nobody knows exactly how long a person would have to wear it to prevent VIIP. “Right now, there’s a million things you could measure, and you kind of don’t even know where to start,” he says.

Photo: DLR

To make matters worse, scientists aren’t even sure Visual Impairment Intracranial Pressure Syndrome is caused by high intracranial pressure, or that zero gravity conditions cause pressure to rise. A study of intracranial pressure during a parabolic flight, which achieves zero gravity for around 25 seconds, revealed an initial spike in pressure during ascension, but at zero gravity intracranial pressure went down. It was the exact opposite result that everybody expected.

Mihael Barrat, an astronaut and the former head of NASA’s human research program, also suffers from VIIP after a six-month mission on the space station in 2009. He thinks measuring intracranial pressure in space is critical to solving this mystery, even if it involves an invasive procedure. One way to do this would be to surgically implant intracranial probes that could monitor pressure at different points throughout the mission.

Barrat also added that this vision impairment syndrome could be just one of many dangers posed to the human body by living in microgravity. “We’re seeing the visual and neural, ophthalmic manifestations of it,” Barratt said. “I’m fairly certain this is a bit more global than that.”