Prolonged periods of time in space may cause brain and optical abnormalities similar to those that can occur in intracranial hypertension of unknown cause, a potentially serious condition in which pressure builds within the skull, according to a study appearing online Tuesday in the journal Radiology.

A team of researchers performed magnetic resonance imaging (MRI) and analyzed the data on the 27 astronauts, each of whom were exposed to microgravity, or zero gravity, for an average of 108 days while on space shuttle missions and/or the International Space Station (ISS). Eight of the 27 astronauts underwent a second MRI exam after a second space mission that lasted an average of 39 days.

"The MRI findings revealed various combinations of abnormalities following both short- and long-term cumulative exposure to microgravity also seen with idiopathic intracranial hypertension," said Larry Kramer, professor at The University of Texas Medical School at Houston, in a statement.

Findings included expansion of the cerebral spinal fluid space surrounding the optic nerve in nine of the 27 (33 percent) astronauts, flattening of the rear of the eyeball in six (22 percent), bulging of the optic nerve in four (15 percent) and changes in the pituitary gland and its connection to the brain in three (11 percent) of the astronauts. The pituitary gland secretes and stores hormones that regulate a variety of important body functions.

The same types of abnormalities are observed in cases of intracranial hypertension where no cause can be found for increased pressure around the brain. The pressure causes swelling of the juncture between the optic nerve and the eyeball which can result in visual impairment.

Bone mineral loss and muscle atrophy are some of the known effects of zero gravity on astronauts. With the onset of longer excursions in space afforded by the ISS, visual changes have also been observed and are now being studied.

"Microgravity-induced intracranial hypertension represents a hypothetical risk factor and a potential limitation to long- duration space travel," Kramer said.

VietNamNet/Viet Nam News