Long space missions harm astronauts' eyes and vision, casting doubt on travel to Mars

Microgravity has deep and surprising effects on the human body, particularly on the eyes and vision of astronauts.

Long-duration space travel has been linked to changes in ocular health that astronauts experience after six to twelve months on the International Space Station (ISS).

These changes, associated with a condition called spaceflight-associated neuro-ocular syndrome (SANS), have alarmed researchers and space agencies.

Impact of microgravity on eyes

The study’s lead researcher, Santiago Costantino, is an ophthalmologist at the Université de Montréal. He discovered that over 70% of astronauts on the ISS are affected by a condition known as spaceflight-associated neuro-ocular syndrome or SANS.

Leading a team at the UdeM-affiliated Maisonneuve-Rosemont Hospital, Costantino embarked on a mission to pinpoint the biomechanical changes that are to blame for this particular disorder.

The group analyzed data from 13 astronauts who had spent a period between 157 to 186 days on the ISS. These astronauts ranged in age, nationality, gender, and space mission experience – providing a diverse group for the study.

Astronauts’ eyes change due to microgravity

The researchers compared three important ocular parameters before and after the space missions.

They looked at ocular rigidity, intraocular pressure, and ocular pulse amplitude. To obtain these data, the team used optical coherence tomography and tonometry.

The findings were nothing less than astonishing. The astronauts’ eyes showed a 33% decrease in ocular rigidity, an 11% decrease in intraocular pressure, and a reduction of 25% in ocular pulse amplitude.

Coupled with these changes, symptoms such as altered focal field, reduced eye size and – in some exceptional cases – optic nerve edema and retinal folds were identified.

The role of weightlessness

Costantino explained the fundamental reason behind these changes. “Weightlessness alters the distribution of blood in the body, increasing blood flow to the head and slowing venous circulation in the eye,” he noted.

This is likely what leads to the expansion of the choroid layer, responsible for nourishing the retina of the eye.

The journey back to normal

While these changes might sound alarming, they are generally not a cause for concern. Even though 80% of the studied astronauts exhibited at least one symptom, their eyes returned to normal once they were back on Earth.

In most cases, simply wearing corrective eyeglasses was enough to address the symptoms developed during the time aboard the ISS.

However, there is an air of caution about future long-duration missions, such as a flight to Mars.

Prolonged microgravity and eye health

Understandably, the impact of prolonged exposure to microgravity on eye health remains a mystery. Currently, no known preventive or palliative measures exist.

For this reason, the research team at Maisonneuve-Rosemont eagerly awaits more data from NASA to continue investigating.

“The observed changes in the mechanical properties of the eye could serve as biomarkers to predict the development of SANS,” said Constantino.

Such findings could be instrumental in identifying astronauts at risk before they develop severe eye problems during long-duration missions.

Preparing for the Mars challenge

As the space community sets its sights on missions to Mars, understanding and addressing the effects of microgravity on astronauts’ vision becomes increasingly critical.

A mission to Mars could last between two and three years, significantly exceeding the six to twelve months that astronauts currently spend aboard the ISS.

This extended duration in microgravity introduces a host of unknowns regarding the progression of SANS and its potential long-term impact on vision and overall eye health.

One promising avenue for mitigating these risks lies in technological advancements and preemptive measures.

Researchers are exploring innovative solutions, such as wearable devices that regulate intracranial pressure or techniques to simulate Earth-like gravitational forces.

Additionally, dietary interventions or pharmaceutical approaches targeting the choroidal expansion and venous circulation in the eye may offer new preventive strategies.

Moreover, this study emphasizes the importance of developing diagnostic tools to monitor ocular health in real-time during spaceflight.

Protecting astronauts’ well-being

Enhanced imaging technologies and portable devices could help astronauts and mission control teams identify early signs of SANS, enabling timely intervention.

The collaboration between researchers, space agencies, and medical professionals will be crucial in paving the way for safer long-duration missions.

As Santiago Costantino and his team continue to analyze new data from NASA, their work represents a significant step forward in safeguarding astronaut health and ensuring the success of humanity’s ambitious journey to Mars and beyond.

The full study was published in the journal Open Journal of Engineering in Medicine and Biology.

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