Research team works to help prevent vision loss linked with space travel

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Researchers at the Medical College of Georgia at Augusta University, have teamed up with Polaris Dawn, the first of the Polaris Program’s 3 human spaceflight missions, to better understand how the eye changes many astronauts experience during spaceflight can ultimately leave them with multiple symptoms once they return to Earth — from a need for new eyeglasses to significant vision loss.

According to a Medical College of Georgia at Augusta University news release, the Polaris Program is a first-of-its-kind effort to advance human spaceflight capabilities while continuing to raise funds and awareness for important causes on Earth.¹

More than 70% of astronauts experience a phenomenon known as Spaceflight Associated Neuro-Ocular Syndrome, or SANS, according to NASA.²

The syndrome can have “a constellation of symptoms, including these changes in vision,” according to Matt Lyon, MD, who is director of the MCG Center for Telehealth.

Astronauts can experience other health issues when body fluids, such as cerebrospinal fluid, shift, which can lead to structural changes in the brain.

“The changes start happening on day one,” Lyon, who also is the J. Harold Harrison M.D. Distinguished Chair in Telehealth, said in the news release. “We are not entirely sure what causes these issues with vision, but we suspect it has to do with a shift in cerebrospinal fluid in the optic nerve sheath. On Earth, gravity pushes that fluid down and it drains out, but in space, it floats up and presses against the optic nerve and retina.”

Lyonn and his team of researchers use handheld ultrasound machines to be able to not only figure out the mechanism behind the changes, but be able to predict which astronauts are most likely to experience those issues.

According to the news release, MCG patented the concept of using portable ultrasound to rapidly visualize damage from pressure and fluid changes in the optic nerve sheath, the layers of protective membranes around the nerve. Lyon is studying how this part of the brain is impacted by increased cranial pressure and mild traumatic brain injuries. Like many other organs, when the brain sustains an injury, it swells and fills with fluid.

The researchers have partnered with URSUS Medical Designs LLC, a Pennsylvania-based biotech company with expertise in ultrasound, to build a 3-D ultrasound machine that could help. A 1-year $350,000 Small Business Innovation Research grant from the National Institutes of Health funded the project to build a device that added another dimension to 2-D transducers.¹

Lyon and members the MCG research team are using those ultrasound machines to screen astronauts and determine if any of them have incompetent or damaged optic nerve sheaths. This could determine whether those astronauts will be more susceptible to the vision changes associated with SANS.

Moreover, Lyon pointed out the research team discovered that when the cerebral spinal pressure goes up with mild traumatic brain injuries (TBIs), there is resulting damage to the sheath that is likely lifelong.

“We think that when astronauts who have experienced concussions or mild TBIs go into space and experience the low-gravity fluid shifts, the sheath dilates from the increase in volume,” he said in the news release. “It is like a tire — a normal tire remains its normal shape as it is filled with air, and the shape doesn’t change. When it’s damaged, like bulges on the side of a tire, the fluid fills the bulges up and the sheath expands. This can cause pressure on the nerve and retina. A damaged sheath is less of a problem on Earth, but in space, the excess fluid has nowhere to go.”

However, the researchers have yet to determine if the vision changes are caused by the sheer volume of fluid, by the associated pressure, or both. The researchers also are training Polaris Dawn crewmembers to use the portable ultrasound machines to measure fluid and pressure in real-time during spaceflight.¹

Lyon explained that if it is simply volume, the team suspects the cerebrospinal fluid goes up, fills this floppy bag and gets stuck.

“It’s almost like not flushing your toilets,” he explained. “You’re creating this toxic environment, because the cerebral spinal fluid (CSF) is what carries toxins away from your eyes and nerves, and instead the toxins sit against the optic nerve, killing it. But it could be that combined with the increased pressure that comes with increased CSF, which would be like getting intermittent hypertension in your eye.”

The next steps for the research include developing and fine-tuning countermeasures that would decrease fluid volumes in the head during spaceflight. For example, the United States space program as well as international space partners use a vacuum-pant device, called lower-body negative pressure, that pulls blood and other fluids down in the body.

Moreover, the researchers’ work will be a part of a range of science and research performed during the course of the mission. Polaris Dawn will also jointly work with 23 institutions, including MCG, on the experiments. Other participating institutions include the Translational Research Institute for Space Health (TRISH); University of Texas, Houston; University of Colorado, Boulder; Baylor College of Medicine; Pacific Northwest National Laboratory; and the U.S. Air Force Academy.¹

References:

1. MCG physicians working to help prevent vision loss associated with space travel. EurekAlert! Published August 22, 2024. Accessed August 23, 2024. https://www.eurekalert.org/news-releases/1055276

2. Risk of Spaceflight Associated Neuro-ocular Syndrome - NASA. NASA. Published March 21, 2023. Accessed August 23, 2024. https://www.nasa.gov/directorates/esdmd/hhp/risk-of-spaceflight-associated-neuro-ocular-syndrome/#:~:text=Contents&text=Exposure%20to%20altered%20gravity%20can