Understanding vision problems in space

Houston-Astronaut Scott Kelly’s recent return to Earth after a yearlong stay on the International Space Station provided an interesting opportunity to study the effects of microgravity on the body-including the eyes and vision.

Kelly experienced vision problems on his previous, shorter missions. According to Air & Space, Kelly suffered “bad middle vision” for a while during his mission in 1999; he wore reading glasses during his mission in 2007; and during his 2010-2011 mission, his eyesight “generally changed in a negative way,” but corrected three months after his return to Earth.

Kelly told Optometry Times (Editor’s note: Yes, we actually spoke to him. It was awesome.) that his vision problems this time around were similar to what he experienced on previous missions.

“I would say it was very consistent with my last flight from a subjective point of view,” Kelly says. “We were collecting more data this time on board, so we’ll have a little better insight into when those changes occurred and how they were in flight vs. how they were on the ground. But I don’t think that-at least subjectively-it was very different from my last experience, which in the beginning you notice some changes and then it levels off. And in this case, stayed that same way the whole flight.”

Optometry Times interviews Scott Kelly

Today, we had the honor of participating in a press conference with astronaut Scott Kelly, who recently returned from a year-long mission aboard the International Space Station. Check out what he had to say about the vision changes he experienced during this mission (and stay tuned for our story-we also got to talk to the leading scientists for the ISS-it was AWESOME.)

Posted by Optometry Times on Friday, March 4, 2016

Scott Kelly and his identical twin brother, Mark, who is also an astronaut, participated in array of studies while Scott was in space and Mark was on Earth. This is the first study of its kind that will be able to compare the health effects of being in space for an extended period of time on two individuals who are nearly genetically identical. According to NASA, researchers will continue to track the health of the brothers over the next year before making those findings available to the public.

Check out all of our coverage from SECO 2016

Vision problems-commonly hyperopia-are one of many concerns for astronauts both while in space and after their return to Earth. According to NASA, about three quarters of International Space Station astronauts experience changes in the structure or function of their eyes during and/or after their mission. Some of these problems do not correct themselves upon return to Earth.

Vision is so often impaired that the International Space Station reportedly stocks a supply of reading glasses with different prescriptions (sounds like they could use a good OD on board, right?). Air & Space recently reported one terrifying incident of an astronaut experiencing vision problems at the worst possible time:

“The highest-priority problem, however, is impaired vision, a condition that returning crew members have reported with increasing frequency,” writes Guy Gugliotta in Air & Space. “One U.S. astronaut discovered during reentry that he couldn’t read the checklist for landing. (Fortunately, crew members know the procedures virtually by heart.)”

Next: Shifting fluids within the body

Shifting fluids within the body

One theory about the reason so many astronauts experience vision problems is that shifting fluids within the body are causing the eye to change shape.

The ongoing Fluid Shifts Study (details available HERE) is investigating these vision problems in space. During space travel, the fluids of the body shift toward the head and move across blood vessel and cell membranes differently than they do on Earth. Researchers think that this shifting of fluids toward the head causes increased pressure in the brain, pushing on the back of the eye and causing a change in shape. Due to this shape change, the retina swells and the entire globe slightly flattens, resulting in hyperopia.

From SECO 2016: Glaucoma and space: What's the connection?

This study aims to:

• Fully characterize this fluid shift

• Determine the relationship between the fluid changes and its impact on the visual problems using tonometry, ocular ultrasounds, and OCT

• Determine individual susceptibility to these problems

To find out how these fluid shifts are affecting vision as well as other things in the body, researchers are collecting a number of measurements at different points throughout an astronaut’s mission including:

• Saliva, urine, and blood tests

• Intracranial pressure

• Intraocular pressure (IOP)

• Ocular structure

• Blood pressure

• Heart rate

• Ultrasound measurements of fluid shifts

The hope is that a special suit designed in Russia called a Chibis suit, or a lower-body negative pressure suit, will help keep the body’s fluids where they need to be. Russian astronauts have long used these suits during the last three weeks of their mission in preparation for their return to Earth; however, studies have not yet evaluated the suits’ effect on fluid shifting and the eye. If the suit is found to have a positive impact on astronauts’ health, astronauts may use the suit earlier or more often during their missions.

John Charles, PhD, human research program associate manager for the International Space Station, told Optometry Times (Editor’s note: Yes, we talked to him, too. It was also awesome.) that while the Russian crew members are required to use this suit in intervals throughout their missions, the American astronauts have never been required to do so. 

“The last time that anybody has done lower-body negative pressure for research purposes was just about 20 years ago, and then before that there were several investigations using lower-body negative pressure as a potential counter measure on several shuttle missions,” says Dr. Charles. “The difference is that this is one of the first times in recent memory that lower-body negative pressure has been done for research purposes. We had to get clearance from the Russian medical community because using this piece of end-of-mission medical hardware for research purposes necessarily reduces its lifetime, its continued usefulness, and the number of times you can decompress in it for future end-of-mission preparations.

“The Russians agreed with us that the investigation was interesting enough and potentially significant enough that it was worth the expenditure of a limited number of runs of the Chibis device,” says Dr. Charles. “It was intended to understand how the fluid shifting that occurs may influence the changes that occur in the ocular system, especially in the shape of the globe of the eye, as well as the pressure inside of the head and the distribution of the fluids throughout the body.”

Dr. Charles says he has not yet seen the results from this investigation, but because Kelly received only six combined total hours using the Chibis, he does not believe that it will have enough of an impact to reverse the fluid shift.

“I’m thinking of it more as an acute, brief, transient intervention to answer a specific question relating to intracranial pressure and the shape of the eye, but the results that come back from that should be very enlightening and illuminating in that regard,” says Dr. Charles.

For more, principal investigator Michael B. Stenger, PhD, of Wyle Science, Technology, and Engineering Group in Houston discusses the study in this video.

Next: Why genetics and nutrition may play a role

Why genetics and nutrition may play a role

In January 2016, NASA announced researchers found a possible link between nutrition, genetics, and the vision problems experienced by astronauts in space. The study was published in published in The FASEB Journal.

Blood samples collected on board the International Space Station suggested chemical differences between astronauts who experienced vision problems and those who did not.

Researchers identified genetic markers that help code the pathway of one-carbon metabolism and a series of chemical reactions at the molecular level that involves several enzymes and requires B vitamins, including folate, vitamin B12, and vitamin B6. The body doesn’t manufacture B vitamins and must obtain them through food.

The results documented significant polymorphisms. Everyone with the “minor” form of that polymorphism developed vision or eye problems to some degree. However, those who did not develop eye problems did not have that form of the polymorphism. For another polymorphism, all but one individual with the “major” form of the polymorphism developed eye problems.

The results suggest that astronauts with these genetic differences and lower B-vitamin status are at a greater risk for vision and other ocular changes while in space.

Scott Smith, PhD, nutritionist at NASA’s Johnson Space Center in Houston and co-author of the paper, calls the results of the study “striking” and says that the results may have significant implications for NASA and future astronauts.

“We’ve identified an associated genetic link in some astronauts who have the vision issues,” Dr. Smith says in the NASA release. “We still don’t know the mechanism, or what is causing the vision issues, but being able to narrow down some of whom to study should help refine research and hopefully will speed finding the cause, and a way to treat, or ideally to prevent these problems from happening.”

NASA says that additional work is needed to determine the mechanism and then to develop at treatment or a way to prevent these problems.

Want to know more about the studies conducted during Kelly’s one-year mission? Click here to check out all of NASA’s research.