How Does Long-Term Spaceflight Affect Vision?

At least 60 percent of astronauts who spend at least a month in space experience negative changes to their bodies due to microgravity and other factors like increased radiation exposure. One potential effect is Spaceflight-Associated Neuro-Ocular Syndrome (SANS), a condition in the eye that can lead to decreased sharpness of vision and swelling and flattening of structures in the eye.

As NASA is gearing up for a return to the moon and eventually a mission to Mars (which would require humans to spend 1.5 to 2.5 years in space), solving this issue has become increasingly important. NASA has chosen researchers from the Texas A&M University College of Medicine to conduct an investigation on the effect of long-term spaceflight on the eyes and on the arteries, veins and lymphatic vessels that serve the eye and maintain vision.

“NASA is worried about the impact that long-term spaceflight will have on astronauts’ health and their ability to complete missions, because of the fact that their vision can be significantly impaired,” said David C. Zawieja, regents professor at the College of Medicine and lead investigator of the experiment. “Their vision can be impaired — it can be temporary, it can be permanent, it can be mild, it can be severe, it can be in one eye more than the other. There’s a lot that we don’t know, but what we do know is that this is a mission-critical problem.”

The project, also known as the Rodent Research 23 (RR-23) mission, launched a total of 20 animal models this past December to the International Space Station (ISS) for a duration of about five weeks. This week, the animal models returned to Earth, delivered to NASA’s Kennedy Space Center in Florida and then flown directly to College Station, where experiments are currently being conducted by specialized teams from the College of Medicine and colleagues.

This is the first time in history that live animals brought back from space are being researched at a non-NASA affiliated institution or group, an arrangement that was partly due to the COVID-19 pandemic’s social distancing measures necessitating more lab space.

Co-investigator teams on this project include those from the labs of Pooneh Bagher, Dr. Anatoliy Gashev, and Travis Hein from the Department of Medical Physiology;and Binu Tharakan from the Department of Surgery at the Morehouse School of Medicine. In addition, Farida Sohrabji and David Earnest from the Department of Neuroscience and Experimental Therapeutics are also helping their respective teams.

In 2017, Zawieja and his colleagues worked on a similar project, called the Rodent Research 9 (RR-9) mission, that studied the effects of long-term microgravity on eyesight. They studied the vascular dynamics in the brain and spinal cord and examined the potential impact of changes in cerebral spinal fluid pressure on animal models they launched to the ISS.

For this RR-23 mission, Zawieja and colleagues are taking a different approach. Instead of studying the micro vessels of the brain, this research focuses on the potential imbalance of the microcirculation in the eye itself, creating local edema particularly near the back of the eye.

“Since astronauts have been spending more than a few hours or even a day or two in space, there is a very well-defined redistribution of body fluids,” Zawieja said. “What happens is they kind of get chicken legs and buffalo torsos and a puffy head and neck because the fluids that will normally drain toward your feet and your legs on Earth now don’t have gravity pulling them down. A lot of fluids will get redistributed centrally and toward the head and neck which produces a number of issues for the astronauts — stuffy nose, puffy face, puffy neck and potentially SANS.”

Currently, the teams are dissecting and examining the various structures of the animal models’ eyes. They also are analyzing the models to see if the vessels are working normally. If they find that the vessels are working abnormally, they will further examine them to see if there is evidence of potential localized edema in the back of the eye that could be compressing the optic nerve and producing the pathology associated with SANS — loss of visual acuity. They will also compare the space animal model results to two other control groups that stayed on Earth.

The teams must dissect and examine the flight animal model within a short time frame before the effects of weightlessness start reversing.

“The idea is to try to catch whatever changes may have occurred before they start reversing,” Zawieja said. “The good thing is we know from other data that it takes probably a minimum of three to five days before these effects start reversing and going back to normal because the vessels will eventually adapt to the local environment that they’re in.”

The research conducted from RR-23 will allow scientists to better understand the impacts of long-term spaceflight on SANS and in the future, create countermeasures that will prevent astronauts from developing SANS. “We suspect that the final analyses from this project will also help determine the future success of longer space missions to destinations like Mars,” Zawieja said.

Zawieja anticipates that the final analyses and examinations of the RR-23 mission will conclude at the beginning of 2022.