Long-term space travel presents numerous challenges for astronaut health, and vision impairment is one of the most significant concerns. A recent study has revealed that 70% of astronauts who spent between six and 12 months aboard the International Space Station (ISS) experienced notable changes in their vision due to a condition known as Spaceflight-Associated Neuro-ocular Syndrome (SANS). This syndrome, which was first officially identified by NASA in 2011, could have serious implications for deep-space missions, including future crewed expeditions to Mars.
What is SANS?
SANS is caused by fluid shifts in microgravity, which increase pressure on the eyes and brain. This pressure leads to several physiological changes, including:
🔹 Swelling of the optic nerve
🔹 Flattening at the back of the eye
🔹 Altered focal field and vision changes
While most astronauts experience temporary vision changes that often reverse after returning to Earth, the long-term effects of prolonged microgravity exposure remain unclear. Given that a round-trip mission to Mars could take two to three years, space agencies are working urgently to find countermeasures to prevent irreversible eye damage.
Early Observations and NASA’s Response
The first indications of SANS were observed in Russian cosmonauts who spent extended durations aboard the Mir space station in the 1990s. However, at the time, SANS was not yet identified as a distinct medical condition. In 2011, NASA formally classified it as a neurological and ocular syndrome based on distinct findings in astronauts’ eye structure and brain pressure dynamics.
The primary suspected cause of SANS is fluid displacement in microgravity. On Earth, gravity naturally pulls bodily fluids downward, but in space, fluids redistribute toward the head, leading to increased ocular and intracranial pressure. However, the exact mechanisms behind SANS remain under investigation.
“Several theories have been suggested, such as hemodynamic fluid shift, exposure to CO₂, and exercise in microgravity conditions,” stated Santiago Costantino, lead author of the new study from the Université de Montréal.
New Research Sheds Light on SANS
Costantino’s team conducted a study involving 13 astronauts who spent five to six months aboard the ISS. The research team examined three key eye measurements before and after spaceflight:
1️⃣ Ocular Rigidity – Reflects the stiffness of eye tissues
2️⃣ Intraocular Pressure (IOP) – The fluid pressure inside the eye
3️⃣ Ocular Pulse Amplitude (OPA) – The variation in eye pressure with each heartbeat
Using advanced imaging techniques, including tonometry to measure eye pressure and imaging of the choroid (the eye’s vascular layer), the study found significant changes:
🔸 33% decrease in ocular rigidity
🔸 11% drop in intraocular pressure
🔸 25% reduction in ocular pulse amplitude
These changes were linked to decreases in eye size, optic nerve swelling, and in some cases, retinal folds. Additionally, five astronauts had a choroidal thickness exceeding 400 micrometers, well above the normal range of 200–300 micrometers in healthy adults. Notably, these changes were independent of age, gender, or prior spaceflight experience.
Implications for Mars Missions
With NASA and other space agencies aiming for human missions to Mars, the risk of permanent vision damage due to prolonged microgravity exposure is a serious concern. Unlike ISS missions, which allow for relatively quick medical interventions, a Mars-bound crew will be isolated for years with limited access to Earth-based healthcare.
Without proven preventive treatments, astronauts on long-duration missions could face progressive vision impairment, potentially affecting mission safety and crew performance.
Potential Solutions and Countermeasures
To address the risks of SANS, researchers and space agencies are working on multiple countermeasures, including:
✅ Pharmaceutical interventions – Medications that may regulate intraocular pressure and fluid dynamics
✅ Nutritional strategies – Adjusting diet to counteract fluid shifts
✅ Negative pressure devices – Specialized suits or tools that draw bodily fluids toward the lower body, relieving head pressure
Future studies aim to refine these solutions and identify biomarkers that could predict astronauts at higher risk of developing severe vision impairment.
“The observed changes in the mechanical properties of the eye could serve as biomarkers to predict the development of SANS,” said Costantino. “This would help identify at-risk astronauts before they develop serious eye problems during long-duration missions.”
The Road Ahead
As space agencies continue to push the boundaries of human spaceflight, understanding and mitigating SANS will be crucial for enabling deep-space exploration. Missions to Mars and beyond will depend on keeping astronauts healthy and operational in challenging environments.
With further research and innovative countermeasures, humanity may soon overcome one of the most significant physiological challenges of long-term space travel. 🚀👨🚀👩🚀
