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Why Astronauts Develop Bad Eyesight After Long-Duration Missions

Why do astronauts have vision problems after spending too much time in space? The answer might be lying in the fluid bathing the brain and the spinal cord, says a new study that attempts to shed light on the topic; the paper has recently been presented at Radiological Society of North America‘s (RSNA) annual meeting.

International Space Station and astronaut in outer space over th

Being an astronaut might be one of the most awesome jobs ever, but as with everything awesome, it comes with a heavy price. Humans are created such that Earth is in synchrony with their very life—conversely, they are not made to live beyond the planet. This is why astronauts spending a prolonged amount of time in space will most likely have to endure painful health consequences, one of which is visual impairment. A form of this predicament is called the visual impairment intracranial pressure (VIIP).

Researchers have attempted to delve into the intricacies of the mechanisms that lead to VIIP, and the team has shown a (possible) reason behind this defect. The new findings suggest that the visual problem is associated with changes in the volume of cerebrospinal fluid (CSF), the fluid bathing the brain and the spinal cord.

VIIP is characterised by blurry vision, and structural changes like flattened eyeballs and optic nerve inflammation. It has been diagnosed in around 66% of astronauts who have previously been on long-duration missions in space onboard the International Space Station (ISS). Research conducted in recent years has shown that some of the astronauts affected by this condition have had irreversible structural modifications upon returning home, explains the lead author of the study, Noam Alperin from the University of Miami Miller School of Medicine. Alperin and his team found a possible source of the anomaly: the CSF. It is to be noted that other scientists have, in the past, identified another probable origin of the problem, namely an upward movement of vascular fluid in the bodies of the astronauts.

Alperin explains that the microgravity of space might be impacting negatively on the CSF.

“On earth, the CSF system is built to accommodate these pressure changes, but in space the system is confused by the lack of the posture-related pressure changes,” says Alperin.

The team made their evaluation of the matter by comparing the high-resolution orbit and brain MRI scans of 7 long-duration-missions astronauts and those of the latter’s counterparts engaged in short-lasting missions. This shows that the former group had a significant increase in both the flattening of their eyeballs and optic nerve protrusion after their flight into space. Furthermore, they displayed significantly larger increases in the volume of the CSF surrounding the optic nerves, and in the volume of ventricular CSF, found in cavities of the brain. The ocular changes that resulted from the flights were linked with greater increases in intraorbital and intracranial CSF volume.

“The research provides, for the first time, quantitative evidence obtained from short- and long-duration astronauts pointing to the primary and direct role of the CSF in the globe deformations seen in astronauts with visual impairment syndrome,” says Dr. Alperin.

The author justifies their work by explaining how these findings will assist researchers in finding protective measures for astronauts who are exposed to microgravity for long amounts of time to prevent irreversible deformations in the eye.

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