Astronauts’ Eyes Get Weaker When They Go On Long Missions To Space

After six to 12 months aboard the International Space Station (ISS), astronauts’ eyes and vision experience significant changes due to the low levels of gravity in space.
An ophthalmologist from the University of Montreal named Santiago Costantino found that at least 70 percent of astronauts on the ISS have been affected by SANS, spaceflight-associated neuro-ocular syndrome.
Costantino runs a biophotonics research unit at the Maisonneuve-Rosemont Hospital, which is affiliated with the university.
For the new study, he assembled a team of researchers to identify the changes that are responsible for this disorder.
They examined data collected on 13 astronauts who spent between 157 and 186 days on the ISS. The average age of the subjects was 48.
They came from the United States, European, Canadian, and Japanese space agencies. Of the astronauts, 31 percent were women, and eight percent were on their first space mission.
The researchers compared three ocular parameters before and after the astronauts’ space missions. The parameters included ocular rigidity, ocular pulse amplitude, and intraocular pressure.
They used optical coherence tomography to measure ocular rigidity. Tonometry was used to measure the other two parameters.
The study’s findings showed significant changes in the biomechanical properties of the astronauts’ eyes. There was a 33 percent decrease in ocular rigidity, a 25 percent decrease in ocular pulse amplitude, and an 11 percent reduction in intraocular pressure.

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These changes came alongside symptoms such as reduced eye size and altered focal field. In some cases, there was optic nerve edema and retinal folds.
In addition, the team found that five astronauts had a choroidal thickness greater than 400 micrometers. This did not align with gender, age, or previous experience in space.
“Weightlessness alters the distribution of blood in the body, increasing blood flow to the head and slowing venous circulation in the eye,” Costantino said. “This is probably what causes the expansion of the choroid, the vascular layer that nourishes the retina.”
The researchers suggest that the choroid’s expansion during weightlessness could stretch the collagen in the sclera, the white outer layer of the eye, leading to lasting changes in the eye’s mechanical properties.
They also believe that a water-hammer effect is created by blood pulsations under microgravity, during which sudden changes in blood-flow-pressure can cause a mechanical shock to the eye and result in the remodeling of tissue.
Generally, these ocular changes are not a cause for concern when the space mission lasts six to 12 months, according to the researchers.
Even though 80 percent of the astronauts they assessed developed at least one symptom, their eyes went back to normal once they had returned to Earth.
Wearing corrective eyeglasses was enough to fix the symptoms that were developed aboard the ISS in most cases. However, experts and international space agencies are concerned about the consequences of longer missions.
The effects of prolonged exposure to microgravity on eye health remain unclear. Currently, no preventive or proper protection measures exist. The research team will continue its investigations once they have received more data from NASA.
The study was published in the IEEE Open Journal of Engineering in Medicine and Biology.
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