Astronaut Mark Vande Hei during a spacewalk. Credit NASA

Space flight-associated neuro-ocular syndrome (SANS) is a known phenomenon impacting astronauts who spend time aboard the International Space Station, which has been studied by NASA eye health professionals from several years.

In the latest study, published in JAMA Ophthalmology, optometrist Nimesh Patel, assistant professor at the University of Houston, quantified some of the changes using customised optical coherence tomography imaging.

"We studied pre-flight and post-flight data from 15 astronauts who had spent time aboard the space station and detected changes in morphology of the eyes. All of them had good vision before and after the flight, but many had a change in the structures of their eyes.”

A/Prof Patel’s algorithms showed that following prolonged space flight, three major changes occur: a change in the position of the Bruch membrane opening; an increase in retinal thickness closer to the optic nerve head rim margin; and an increase in the proportion of eyes with choroidal folds.

While some of these changes would be expected in patients with elevated intracranial pressure, there are also significant differences, he said, for example, choroidal folds are not as prevalent in individuals with intracranial hypertension. Although the exact cause of the changes remains unknown, A/Prof Patel hypothesized that they are a result of microgravity-associated orbital and cranial fluid shifts.

Because some astronauts included in the study had previous spaceflight experience, the pre-flight data was first compared with healthy control subjects before comparisons with post-flight scans.

"The results of these investigations suggest that, although there may be resolution of structural changes, there could be long-term ocular anatomical changes after extended-duration space flight," said A/Prof Patel.