Under pressure

A lack of circadian rhythm in the skull has been pinpointed as the cause of vision problems in space


“And the stars look very different today,” the famous David Bowie song goes, “For here am I sitting in a tin can far above the world.” Researchers may have discovered the reason for this particular space oddity.

Skull pressure has been pinpointed as the cause of vision deterioration among astronauts who spend lengthy periods in space.

A new study published in The Journal of Physiology suggests the reason many space explorers experience vision problems is because of the constant intracranial pressure experienced at zero-gravity, compared to a variation in pressure between day and night on earth.

University of Texas Southwestern Professor of Internal Medicine, Dr Benjamin Levine, told OT that a change in vision was the number one health risk for astronauts who spent extended periods of time at the International Space Station. The new research shows that intracranial pressure in zero gravity conditions is higher than when people are standing or sitting on earth, but lower than when people are sleeping.

The study reports that this constancy of pressure on the back of the eye causes the vision problems that astronauts experience over time.

Eight volunteers were flown by NASA flight crews through steep parabolic flights that created 20-second intervals of weightlessness. The volunteers all had ports capable of measuring intracranial pressure permanently placed in their heads as part of cancer treatment.

The researchers measured intracranial pressure during the zero-gravity intervals and compared these with intracranial pressure during standard times of sitting, lying face upward and lying with the head inclined downward.

Researchers are hopeful that now they have isolated the cause of eye problems in space, they can begin work on preventing the vision changes.  

One solution would be to use a vacuum device to lower pressure for part of each day.

Researchers have previously shown that a negative pressure box that snuggly fits the lower body can lower intracranial pressure when applied for 20-minute periods. They hope to test whether the same effect is seen over an eight hour period.

UT Southwestern Instructor in Internal Medicine, Dr Justin Lawley, explained that astronauts were supine for the entire time that they were in space.

“The idea is that the astronauts would wear negative pressure clothing or a negative pressure device while they sleep, creating lower intracranial pressure for part of each 24 hours,” he told OT.