Article Highlights

• SANS is a microgravity-specific condition caused by upward fluid shifts in space that increase pressure in the head and eyes.
• The syndrome leads to optic nerve swelling, choroidal folds and a hyperopic shift requiring stronger corrective lenses.
• Symptoms typically develop after weeks to months in space and generally resolve after return to Earth, though some structural changes may persist.
• Risk appears dose-dependent, with longer-duration missions posing greater concern for neuro-ocular changes.
• Ongoing Houston Methodist-NASA research is focused on improving in-flight diagnosis, monitoring and care using portable, real-time medical technologies.

A new video from neuro-ophthalmologist Dr. Andrew G. Lee, the Herb and Jean Lyman Centennial Chair of Ophthalmology at Houston Methodist Hospital and the Blanton Eye Institute, explores a medical phenomenon unique to space travelers: spaceflight-associated neuro-ocular syndrome (SANS).

Dr. Lee is an internationally recognized expert in SANS, a condition that causes temporary vision degradation while in space.

The syndrome occurs exclusively in the microgravity environment of space, where the absence of gravitational forces causes fluid to accumulate in astronauts' heads, resulting in significant changes to the eyes.

"Under normal conditions on Earth, gravity pulls down on our bodily fluids, keeping them aligned with our heart, lungs and legs," Dr. Lee explains in the video. "But in zero gravity, fluids shift upward, causing increased pressure in the head and eyes."

Manageable but concerning

This fluid shift can lead to a range of eye-related symptoms, including swelling of the optic nerve, choroidal folds (wrinkling of the eye tissue) and a hyperopic shift that necessitates stronger glasses.

While the symptoms of SANS, such as blurred vision and optic nerve swelling, typically resolve upon astronauts' return to Earth, structural changes to the eye sometimes persist. Fortunately, no astronaut has experienced permanent vision loss due to the condition.

“The insights gained from studying SANS could help us better understand similar conditions on Earth, such as fluid buildup and optic nerve swelling seen in neuro-ophthalmology patients”

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Dr. Andrew G. Lee
Herb and Jean Lyman Centennial Chair of Ophthalmology at Houston Methodist Hospital and the Blanton Eye Institute

SANS usually develops after a few weeks to months in microgravity and poses a significant concern for long-term space missions, such as establishing a lunar base or sending a crewed mission to Mars.

"It's important to figure this out because spaceflight-associated neuro-ocular syndrome is a dose-dependent phenomenon, meaning the longer you're in space, the more substantial the risk," says Dr. Lee. "A round-trip crewed mission to Mars is likely to take upwards of two years, much longer than the typical six-month tour of duty on the International Space Station. We don't know the impact of such a long deployment."

Houston Methodist-NASA connection

Ongoing research into SANS, a joint venture by Houston Methodist and NASA, aims to predict, monitor, treat and prevent the syndrome. Despite the challenges of studying a condition that occurs only in microgravity, Dr. Lee is leading efforts to better understand SANS. Tests such as MRI and spinal tap, while useful, are difficult to safely perform in space, complicating research efforts.

However, Houston Methodist and NASA are collaborating on developing innovative solutions, including artificial intelligence-enabled portable, lightweight, wearable medical consultation devices. These devices aim to provide real-time diagnostic capabilities, a necessity given the substantial 20-minute communication delay between Earth and Mars.

The goal is to ensure that astronauts receive timely care and monitoring for SANS and other related conditions, representing a landmark in long-distance telemedicine.

Dr. Lee concludes the short whiteboard video with a nod to Houston's storied connection to space exploration.

"Houston was the first word spoken from the moon, and I, for one, am looking forward to hearing our city's name again when we reach the surface of Mars," he concludes.