Paolo Rossi Castelli 13 January 2022 6 min read

A cure for astronauts’ eyes

Experiments have been successfully carried out in the U.S. using a special sleeping bag that helps transfer bodily fluids towards the feet, to stop them accumulating in the skull and damaging the eyeballs in the absence of gravity.

Spaceflight Associated Neuro-ocular Syndrome (SANS) has long worried those studying astronauts' who stay in orbit in micro or zero gravity environments, both for a long or short amount of time.

The syndrome typically causes the eyes to swell, and progressive loss of the balanced proportions of the eyeball volume, loosening the optic nerve and causing impaired vision: all due to a reduction in normal intracranial pressure caused by less, or no, gravity.

The phenomenon has been known for at least a decade. It starts to occur after just a few hours in orbit, and gets worse when astronauts are asleep, as when the body is lying on its back fluids tend to distribute everywhere, compressing cerebral tissue and everything else inside in the skull, which then affects vision.

The consequences can also be very serious, because significantly impaired vision can jeopardise how tasks are performed in the spacecraft. This visual impairment can continue even after astronauts return to earth. According to NASA, more than half of those who have spent over three months on the International Space Station have suffered from SANS, so a cure needs to be found.

 A range of solutions have been suggested in the past to remedy the problem, but none have proved truly effective, or they have only prevented and not cured the effects. Now, however, a negative pressure sleeping bag developed by a team at Southwestern University in Dallas (Texas), headed by Benjamin Levine, which has been working on aerospace medicine for years, could be a real step in the right direction. This has been demonstrated by data obtained from ten volunteers who used it.

Three days lying in a simulator
The scientific journal JAMA Opthalmology reports that ten volunteers (half of whom were women), aged between 18 and 55 and with an average age of 29, lay in a space simulator for three days to measure test parameters, both while awake and asleep. None of the volunteers suffered from any heart, kidney or eye diseases. For the following three days, they spent eight hours a day in a special sleeping bag which exerted a negative pressure equal to 20 millimetres of mercury on the lower part of their bodies, preventing fluids moving to the skull and causing them to flow towards the feet instead.

So the device, which is an optimised version of similar solutions tested over the years, worked and appears to prevent neuro-ocular syndrome.

An aid for trips to Mars
Further studies need to be carried out on the negative pressure sleeping bag, to understand, for example, the optimal amount of time to spend in the bag and the best pressure conditions. But it could be used in space missions (especially those that will take humans to Mars - a journey expected to last around two years), to prevent the long-term consequences of SANS, which are currently unknown.

This new type of sleeping bag could also reduce the risks of other negative effects associated with microgravity. For example, irregular heartbeats or the state of mental confusion experienced by several astronauts (which they call space stupidity), whose origin is unknown but may also be produced by changes in fluids inside the skull.


Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.