Astronauts’ vision deteriorates during long flights

Scientists have investigated how long stays in space affect astronauts’ vision. It turned out to be getting worse. This could seriously affect plans for a human mission to Mars, as it should last several months.

Astronauts’ vision gets worse. Source: www.forbes.com

Microgravity affects vision

Low gravity (microgravity) in space causes significant changes in astronauts’ eyes and vision after 6-12 months aboard the International Space Station (ISS), according to a study published in the IEEE Open Journal of Engineering in Medicine and Biology.

University of Montreal ophthalmologist Santiago Costantino found that at least 70 percent of astronauts on the ISS suffered from spaceflight-associated neuro-ocular syndrome, or SANS.

In the biophotonics department he heads at Maisonneuve-Rosemont Hospital, part of the UdeM, Costantino gathered a team of researchers to identify the biomechanical changes responsible for the disorder. 

They analyzed data collected by NASA’s Canadian team on 13 astronauts who spent between 157 and 186 days on the ISS. The average age of the study subjects was 48, and they represented space agencies from the United States, Europe, Japan, and Canada; 31% were women; eight were on their first mission.

Three ocular parameters

The researchers compared three ocular parameters before and after astronauts’ space missions: ocular rigidity, intraocular pressure, and ocular pulse amplitude.

They measured the rigidity of the eye using optical coherence tomography with a special video module to improve the quality of images of the ocular vasculature. The other two parameters, intraocular pressure and ocular pulse amplitude, were measured by tonometry.

The study revealed significant changes in the biomechanical properties of the astronauts’ eyes: a 33% decrease in ocular rigidity, an 11% decrease in intraocular pressure, and a 25% decrease in ocular pulse amplitude. These changes were accompanied by symptoms such as decreased eye size, focal field changes, and in some cases, optic nerve edema and retinal creases.

The researchers also found that five astronauts had eye vasculature thicknesses greater than 400 micrometers, which did not correlate with age, gender or previous space experience. 

Long-term changes

According to the researchers, the expansion of the vasculature during weightlessness could stretch the collagen in the sclera, the white outer layer of the eye, causing long-term changes in its mechanical properties.

They also believe that blood pulsations in microgravity can create a water hammer effect, where sudden changes in blood flow pressure cause a mechanical shock to the eye, resulting in significant tissue remodeling.

Eye condition recovers

According to the researchers, these eye changes are generally not a concern if the space mission lasts six to twelve months. Although 80% of the astronauts they studied developed at least one symptom, their eyes returned to normal after returning to Earth.

In most cases, corrective eyewear was sufficient to manage the symptoms that developed aboard the ISS.

However, the research community and international space agencies are cautious about the implications of longer missions, such as a mission to Mars. The effects of long-term exposure to microgravity on eye health remain unknown, and preventive or palliative measures do not exist yet.

“The observed changes in the mechanical properties of the eye could serve as biomarkers to predict the development of SANS (spaceflight-associated neuro-ocular syndrome),” said Costantino. “This would help identify at-risk astronauts before they develop serious eye problems during long-duration missions.”

According to phys.org

Advertising