Space Agencies Race to Understand Why Astronauts Are Losing Their Eyesight

The European Space Agency (ESA) is investigating why astronauts experience vision loss during spaceflight, hoping to find ways to treat or even prevent the condition as future missions grow longer and the risk of permanent eye damage rises.

ESA has commissioned British startup Siloton to develop a solution using quantum technology that shrinks the core components of standard optometry equipment onto a photonic chip smaller than a coin. Founded by physicists in 2020, Siloton already works with the UK's National Health Service, letting patients with retinal conditions scan themselves at home.

A widespread problem

Spaceflight-associated neuro-ocular syndrome (SANS) affects roughly 70 percent of astronauts aboard the International Space Station. It occurs when bodily fluid, no longer controlled by gravity, accumulates in the head, compressing the eyeballs, swelling the optic nerve, and pushing the retina forward. One notable case involved NASA astronaut John Phillips, who launched to the ISS in 2005 with 20/20 vision but returned six months later with vision measured at 20/100, a moderate visual impairment.

While some damage reverses after returning to Earth, space agencies remain concerned about both the operational risk of vision loss during a mission and the longer-term health consequences.

Automated scanning without ground support

Astronaut eyes are currently monitored on the ISS with a bulky device that requires real-time guidance from experts on Earth. As missions venture farther into deep space, growing communication delays will make that approach impractical. Siloton's device would let astronauts scan their retinas more often without needing ground support, generating more data that could reveal early signs of eye changes.

Engineers still face technical hurdles, including avoiding batteries due to fire risk aboard spacecraft and finding ways to keep an astronaut's head steady without gravity. Siloton notes that adapting the technology for elderly patients with existing vision problems is actually more challenging than the work planned for young, healthy astronauts, and that the space research is expected to improve the device's eventual use in everyday healthcare as well.