Nearly two-thirds of astronauts, after returning from space, have reported having vision problems. UT Southwestern researchers may have found the cause.
A team from UT Southwestern recently discovered that damage to eyesight may be due to the absence of a changing, day-to-night cycle of skull pressure in space. The team published their findings on Jan. 16 in the Journal of Physiology.
Deemed the most critical health problem for astronauts in space, the study linked the mysterious vision problem to structural changes in astronauts’ eyes, said Benjamin Levine, UT Southwestern professor of internal medicine and last author of the study.
“If you look behind (astronauts’) eyes...there’s evidence that there’s damage,” Levine said. “It looks like it’s getting squashed from behind.”
The researchers had previously noted that astronauts have similar symptoms to those caused by elevated pressure inside the brain and set out to study how zero-gravity affects this pressure, called intracranial pressure.
During this study, eight volunteers, assisted by NASA, were subjected to simulated zero-gravity and low gravity conditions. Researchers measured the pressure in volunteers’ brain tissue as they stood up or laid down, and compared the measurements to those taken on earth at normal gravity.
In earth conditions, intracranial pressure is higher when lying down, and decreases after sitting up. The researchers found that low or zero-gravity conditions in space prevented a decrease in intracranial pressure from occurring, keeping intracranial pressure relatively high at all times. These results imply that day-to-night cycles on earth protect brains from illness caused by high intracranial pressure, according to the study.
“You spend most of your days hopefully upright and not (lying down),” Levine said. “The human body is use to 16 hours a day of low pressure and 8 hours a day of higher pressure. In space, you can’t stand up, so the pressure is not pathologically elevated, but the brain can never get a rest.”
However, scientists need to conduct further research to fully understand how zero-gravity affects eyesight, said Rong Zhang, UT Southwestern associate professor of internal medicine and co-author of the study. Intracranial pressure may affect the shape of eyes or cause swelling, but the mechanism is not clear, Levine added.
“We do not know the magnitude and potential impact of this problem, which may depend on the duration of space travel, individual tolerability, as well as the severity of the damage and the underlying pathophysiological mechanisms,” Zhang said.
In order to solve this problem, researchers hope to design devices that will simulate the pressure from standing upright during the day. Levine and colleagues are currently working with a garment company to create a negative pressure sleeping bag, which works by drawing blood away from the brain and lowering intracranial pressure.
“Now can we lower the pressure inside the brain and it give it a rest,” Levine said.