New research could lead to the creation of equipment designed to reduce the deterioration of astronaut vision over the course of prolonged trips beyond Earth's protective atmosphere. According to the newly published study, the root cause of the degradation of vision is a lack of pressure variation in an astronaut's cranium.

NASA and its partners are actively seeking to address the effects of microgravity on the human eye as part of a more comprehensive effort to advance its ability to maintain an astronaut's physical health in the space environment in preparation for the next phase of manned space exploration. The push comes as NASA advances towards its grand ambition of sending a crewed mission to Mars.

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The new study, which was carried out by an international team of researchers, asserts that a serious factor in vision loss could be the steady intracranial pressure experienced by an individual in the zero-gravity environment of space.

In order to determine the effect that a lack of significant gravity has on the human cranium, the team recruited eight volunteers who had received a specific form of treatment for brain cancer known as an Ommaya reservoir. The intraventricular catheter system, also referred to as a port, allowed the researchers to measure the intracranial pressure of the study participants.

To mimic the microgravity environment, the volunteers were subjected to a series of parabolic flights, allowing the participants to repeatedly experience 20 seconds of weightlessness as the aircraft executed a number of controlled dives.

Cancer patient and volunteer Trent Barton imaged lying down during the parabolic flight (Credit: David Ham)

The intracranial pressures recorded during the flights were then compared to measurements taken while the volunteers were either sitting, lying facing upward and lying with their heads tilted downwards here on the ground. It was discovered that, during periods of weightlessness, the intracranial pressure of the volunteers remained steady at a level slightly below that which would be expected of an individual who had assumed the supine position on Earth.

Ordinarily, the back of a person's eye would experience a range of pressures over the course of a standard day on Earth. Periods of standing coincide with the lowest levels of intracranial pressure, as blood is drawn away from the head by Earth's gravity. The highest levels of intracranial pressure are normally experienced when a person lays down to rest for the night in the supine position.

The parabolic flights showed that individuals living in very low gravity environments such as that prevailing aboard the International Space Station (ISS) do not experience these pressure cycles. Instead, the team believe that the constant levels of relatively high intracranial pressure are responsible for somehow remodeling the back of astronauts' eyes.

The researchers are now working to establish whether a negative pressure device, if worn while an astronaut sleeps, could be used to mitigate the intracranial pressure and reestablish a more ordinary pressure cycle.

One method by which this could be achieved is with the use of a negative pressure box. The box is placed around the lower body of an astronaut, and a negative pressure device draws the individual's blood away from the head and below the heart, mimicking the gravity effect of standing on Earth.

A paper detailing the study has been published online in The Journal of Physiology.

Source: University of Texas Southwestern Medical Center

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