Space Agencies Are Trying to Keep Astronauts From Losing Their Sight

Published 10 August 2026 · science

The European Space Agency is trying to understand why astronauts lose their eyesight in space, in the hope they can figure out how to treat—or

The European Space Agency is trying to understand why astronauts lose their eyesight in space, in the hope they can figure out how to treat—or even prevent—the condition as looming longer spaceflights heighten the risk of permanent vision damage. The agency has commissioned British eye-scanning startup Siloton to develop a solution ahead of the international Artemis flights to the moon and other deep space missions. The health tech uses quantum technology to shrink core components used in eye-testing equipment found at optometrists to fit on a photonic chip smaller than a coin. Founded by physicists in 2020, Siloton is currently working with the UK’s Health Service to enable patients with retinal conditions to self-scan at home.

“The ESA pretty much has the same requirements,” says cofounder and chief technology officer Euan Allen. “It's just in a totally different environment.” Spaceflight-associated neuro-ocular syndrome (SANS) is a collection of eye and brain changes caused by spending prolonged periods in a low-gravity environment, and it impacts around 70 percent of astronauts on the International Space Station, according to NASA. One of the starkest cases is that of NASA astronaut John Phillips, who launched to the ISS in 2005 with 20/20 vision, and splashed down six months later with his vision at 20/100—what’s considered a moderate visual impairment. While he was in space, bodily fluid, uninhibited by gravity, built up in his head, squashing his eyeballs, swelling his optic nerve, and pushing his retina forward.

Courtesy of Siloton While returning to Earth can reverse some of the damage, space agencies are concerned by both the operational risk of astronauts losing their vision mid-mission, as well as the longer-term health impacts. “The eye condition SANS is a serious health risk facing astronauts on long missions,” says Rebecca Evernden, director of the UK Space Agency. Medical engineers want to develop their understanding of the condition and the factors causing it so that they can manage any ocular damage, and eventually treat it or even stop it from becoming a problem. Scientists are already monitoring how spaceflight impacts the human eye on the ISS using a modified version of the device found in optometry offices that measures the thickness of layers at the back of the eye.

However, the device is bulky and requires real-time remote guidance from experts on the ground. As astronauts journey further into deep space, lengthening communication delays with Earth will mean this is no longer feasible. Siloton’s device would allow astronauts to scan their retinas more frequently by automating some of the process so that examinations do not need ground support. The ESA hopes that will generate more data on any ocular degeneration, and possibly provide early warning signs that changes in the eye may be occurring—even before they result in vision change.