Going to space is a dream for many, but it doesn’t come without serious health risks. Our body has a fantastic ability to adapt to the extreme environment, but microgravity leads to several conditions, especially during long flight.
One of them is called visual impairment intracranial pressure (VIIP), which causes astronauts to have impaired vision, with about two-thirds of astronauts on long-term missions reporting the condition. An analysis showed that the astronauts’ eyeballs had become flattened at the back, which in turn was responsible for inflaming the optic nerve.
The cause of VIIP has puzzled scientists for years, but a new study has finally pinpointed the cause of this condition. The scientists think the culprit is changes in the volume of cerebrospinal fluid (CSF), which is found in the brain and spinal cord. Their finding was presented at the annual meeting of the Radiological Society of North America.
"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," lead author Dr Noam Alperin, professor of radiology and biomedical engineering at the University of Miami, said in a statement.
A before and after MRI image of an astronaut's eyes. Alperin et al.
On Earth, the CSF balances out the different pressures the eye might experience when we change posture. But in space, due to microgravity, the eye doesn’t know up from down and it slowly deforms as the fluid becomes equally distributed around the nervous system.
The team took before and after high-resolution MRI scans of astronauts from seven long-duration missions and nine short-duration ones.
Long-duration astronauts had an increased flattening of the eye and a higher volume of CSF behind the bulb compared to short-duration crews. The analyses also showed that the higher the volume of CSF, the larger the deformation observed.
"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," said Dr Alperin.
The team is looking to simulate the conditions that lead to the effect and then plan some countermeasures. This would be useful for astronauts, as they risk these effects becoming irreversible during long missions.
The eye flattens and the optic nerve is bent by the CSF. Alperin et al.