A comprehensive National Aeronautics and Space Administration (NASA) study has found that space missions of six months or more result in significant alterations to astronauts' eyes and vision, posing a considerable challenge to the intended mission to Mars.
The condition, known as Spaceflight-Associated Neuro-Ocular Syndrome (SANS), is a top priority for NASA's Space Medicine team.
Scientific studies that included close studies of astronauts identified structural and visual defects in all the participants.
The most frequent ones are flattening of the posterior surface of the eyeball, changes in the retina, and changes in the optic nerve.
These changes may persist for many years after astronauts return to Earth. In a larger study (300 astronauts), the best results were that almost half of long-duration mission astronauts had problems with both near and far vision.
The central issue NASA faces is that a round-trip to Mars would take three years, which may cause irreversible sight damage or blindness that cannot be corrected in space.
The most popular theory posits that fluid shifts toward the head under prolonged exposure to microgravity may cause these eye problems.
To become more familiar with SANS, astronauts on the International Space Station (ISS) are currently undergoing frequent eye exams, including ultrasound and intraocular pressure tests.
Although the underlying cause is not yet known, it is thought to pose a high risk to deep space mission planning, as scientists are in a hurry to develop ways to prevent astronauts' eyesight on the way to Mars.