Traveling in space has many odd effects on the human body. One of the strangest has to do with vision.

After spending some time on the International Space Station, many astronauts discover that they cannot see as well as they do on Earth. The effect is so well known that members of the crew routinely pack "space glasses" to correct their vision in orbit.

Researchers still aren't sure what causes the problem, but they would like to solve it before humans travel beyond low-Earth orbit. A trip to Mars could take at least three years - five times as long as a mission to the station. So it's important to learn about the adverse effects of microgravity on vision and develop ways to counter them.

Christian Otto of the Universities Space Research Association in Houston, Texas, is one of the researchers trying to get a clearer understanding of "space vision." He is the Principal Investigator of the Ocular Health study now underway on the space station.

An accomplished off-road triathlete with an interest in human performance in extreme environments, Otto is well-suited to this PI role. He once toted an ultrasound machine up Mount Everest to study the effects of oxygen deprivation on intracranial pressure. Now, with the Ocular Health study, he's remotely conducting similar tests on astronauts.

"Testing astronauts before, during, and after their missions to the station shows us their status preflight and helps us identify changes that result from the environment and microgravity on the station," explains Otto.

On the space station, the body's fluids, particularly the blood supply, shift toward the head much like what happens on Earth when you lie down. Therefore, it is hypothesized that the pressure inside the skull increases. That increase in intracranial pressure is believed to be transmitted to the eye and optic nerve, leading to changes in eye structure and visual acuity.

Optic Disc Edema (ODE) - swelling of the optic disc - is the most critical change. If it persists, it can lead to a loss of peripheral vision and eventual blindness. Astronauts have experienced only mild ODE to date, but no one knows how severe it could become on a Mars expedition.

"Data from this study will help researchers develop countermeasures for and reduce susceptibility to issues like ODE," says Otto. "It will help us develop targeted treatments to prevent problems."

Adding preliminary data from the Ocular Health study to data from previous Vision Impairment and Intracranial Pressure (VIIP) studies, Otto and his team have made some interesting discoveries.

"Around 70% of 33 International Space Station crewperson subjects have experienced mild VIIP, and we are finding that men are affected about twice as severely as women.

ODE is measured on a scale of 0-5, with 1 being the least effected and 5 being the most. Six out of seven subjects with ODE were grade 1, while the 7th subject had a grade 3 eye. All seven subjects that developed clinical grade ODE were men.

Results from the Ocular Health study will help doctors better understand disorders such as glaucoma and Idiopathic Intracranial Hypertension (IIH) that can plague people back on Earth. The latter is a condition in which cerebrospinal fluid pressure rises and remains elevated for a long time, causing severe headaches that even the strongest pain medications can't touch. Like glaucoma, the condition sometimes leads to vision loss and blindness.

Says Otto,"This study will tell us more about noninvasive measurement of intracranial pressure. The way doctors measure it now is through a spinal tap or making a burr hole in the skull and inserting an intraventricular monitor."

"We are pushing the envelope in several areas of terrestrial clinical medicine. NASA's Ocular Health study is providing new insights in neurology, neurosurgery, ophthalmology, and cardio-vascular physiology. The clinical community is very excited."