Would-be space tourists may be put off their galactic dreams by new research that shows time spent in space can cause eye damage.
Problems with astronauts’ eyesight have been reported for over a decade, prompting the research. For this study, published in the Journal of Engineering in Medicine and Biology, Université de Montréal ophthalmology experts analysed data from “26 eyes from 13 crew members who spent 157 to 186 days on the International Space Station”. The group studied comprised a range of nationalities, with astronauts hailing from Canada, Europe, Japan, and the US. Around a third were women, and, notably, eight were on their first mission.
Shrinking eyes, focal changes and optic nerve swelling
The researchers found that a huge proportion of the astronauts, over 70%, were suffering from spaceflight-associated neuro-ocular syndrome (SANS). Three eye-related factors in particular were looked at: ocular rigidity, intraocular pressure, and ocular pulse amplitude. All three factors were found to have declined, rigidity by as much as 33% – biomechanical changes that result in symptoms such as eyes getting smaller, focal field alterations, swelling of the optic nerve and retinal folds.
What’s more, five of the astronauts were found to have thickening of the middle layer of the eye (the choroid), which is filled with blood vessels that bring in oxygen and nutrients. There was no correlation between the thickening and age, gender or prior time spent in space. Instead, the way weightlessness affects and slows down blood flow is likely to be the culprit, the researchers say. This can stretch the eye’s collagen causing lasting changes.
Corrective glasses and mission length are key
Another worrying aspect of microgravity is what the team terms the “water-hammer effect” of sudden pressure changes which shock the eye and change its tissues significantly.
While these findings may be concerning to anyone with spaceflight ambitions, most space tourists will probably be safe from harm, unless they have designs on going long-haul to Mars. This is because, on missions with a duration of between six months and a year, 80% of astronauts suffer at least one of these problems, but wearing glasses on board helps to mitigate the issue and the eyes usually return to normal when the astronauts come back down to Earth.
