Astronauts’ eyes weaken during long stays in space

The microgravity to which astronauts are subjected in space, when they stay 6 to 12 months on the International Space Station (ISS), makes their eyes more flexible and weaker.

This is what the results of a study led by Professor Santiago Costantino, from the Department of Ophthalmology at the University of Montreal, reveal, which appeared in the Journal of Engineering in Medicine and Biology.

Track the signs of a particular syndrome

Professor Costantino and his colleagues from the biophotonics research unit – of which he is the director at Maisonneuve-Rosemont hospital – had the mandate to uncover the biomechanical changes responsible for the neuro-ocular syndrome associated with spaceflight, which affects at least 70% of ISS crew members.

They therefore analyzed the data obtained by the Canadian NASA team, based on measurements taken from 13 astronauts who stayed 157 to 186 days on the ISS. The participants, 31% of whom were women, had an average age of 48 years and came from the American, European, Japanese and Canadian space agencies. Eight of them were on their first mission.

Based on data collected before, during and after the astronauts’ stay in orbit, the researchers measured three ocular parameters before and after spaceflight: ocular rigidity, intraocular pressure and ocular pulse amplitude.

To do this, they used optical coherence tomography with a personalized video module as well as a tonometer – a device that measures intraocular pressure.

Less rigid and less blood-supplied eyes

“The results show significant changes in the biomechanics of the eyes of astronauts subjected to microgravity: ocular rigidity decreases by 33%, intraocular pressure decreases by 11% and ocular pulse amplitude is reduced by 25%,” write the signatories of the study.

Symptoms commonly seen in astronauts include a decrease in eye size, change in focal field, and in some cases, swelling of the optic nerve and the appearance of folds in the retina. The researchers also noted that five astronauts had choroidal thickness greater than 400 micrometers, an observation that is not correlated with age, gender, or previous space experience.

“Zerogravity changes the distribution of blood in the body, causing blood to rise to the head and slow venous circulation in the eye, and this change likely leads to swelling of the choroid, the vascular layer that nourishes the retina,” underlines Santiago Costantino.

According to him and the members of his team, the expansion of the choroid during weightlessness “could stretch the scleral collagen, lastingly modifying the mechanical properties of the eye and the blood pulsations in microgravity could also create a “hammer effect”. water” leading to remodeling of ocular tissues.

Long-term missions to monitor

For stays of six months to a year, these changes are generally not of concern, according to the study authors. In fact, 80% of astronauts had presented at least one of the symptoms listed, but their eyes returned to normal after their return to Earth. Wearing fitted glasses is enough to correct the symptoms on board the ISS in most cases.

The research community and international space agencies are, however, cautious about the consequences of future long-duration missions, particularly to Mars, since the effects of prolonged exposure to microgravity on eye health remain unknown and no preventive or palliative measure currently exists. The team is also awaiting new data from NASA to evaluate other proposed measures to better understand these symptoms.

“The observed changes in the mechanical properties of the eye could serve as biomarkers to predict the development of the syndrome and could potentially help identify astronauts at risk before they suffer serious eye problems during prolonged missions,” concludes Santiago. Costantino.