NASA’s Twins Study Indicates Multiple Spaceflights Compound Vision Problems

Some vision problems that occur in long-term spaceflight may persist from a previous mission and worsen in a subsequent mission, according to NASA’s Twins Study. The space agency released the results of the study April 11.

The study also suggests that genetics, when combined with lengthy space travel and relentless lack of gravity, may play a role in vision issues.

The Twins Study involved 10 research teams from around the US assembled to analyze physiological, molecular, and cognitive changes in astronaut Scott Kelly during a nearly year-long stay on the International Space Station. The teams compared his results with those of his identical twin brother, retired astronaut Mark Kelly, on Earth.

Scott Kelly showed signs of spaceflight-induced cephalad (headward) fluid shift, as measured by distension of and increased pressure in the internal jugular vein inflight at levels similar to those while lying face up on Earth. This vascular engorgement may contribute to congestion of the vasculature supplying the retina, researchers said.

Scott Kelly experienced increases in subfoveal choroidal thickness (primary vascular supply of the outer retina) and total peripapillary retinal thickness, indicating retinal edema formation.

He exhibited choroidal folds during preflight testing, and the severity of the choroidal folds increased during spaceflight in number and depth. Choroidal folds were not present at baseline for Mark Kelly.

In the weightlessness of space, astronauts often experience increased cranial pressure, headaches, swelling in the face, stuffiness, and changes in vision. NASA said that, as of May 2017, about 40 percent of astronauts have experienced one or more of the following ocular issues: optic disc edema, hyperopic shifts, globe flattening, cotton-wool spots, or choroidal folds. These changes have been termed spaceflight-associated neuro-ocular syndrome (SANS).

Scott Kelly was in space from March 27, 2015, to March 1, 2016, and circled the Earth 5,440 times. A veteran of three previous missions, Scott Kelly had seen his vision degrade during or after space travel, including experiencing poor intermediate vision after a 1999 trip. At the time of the mission, the 50-year-old wore glasses for distance, but said he had no serious vision problems.

Twins Study researchers also noted a decrease in urine leucine-rich alpha-2-glycoprotein (LRG1) levels in Scott Kelly inflight relative to those pre- and postflight. LRG1 has been reported to play a role in retinal vascular pathology.

Predisposition to develop these ocular changes during spaceflight has been associated with low serum folate levels, researchers said. Serum folate, a B vitamin, was low in Scott and Mark Kelly.

Predisposition also has been linked with the presence of specific single nucleotide polymorphisms (SNPs). Risk alleles in five SNPs predict incidence of ophthalmic issues, and six of the nine risk alleles are present in the twins.

The Twins Study will help NASA plan for a trip to Mars, which will require about three years of space travel (six months of travel time, plus time spent on the surface of Mars and orbiting the planet). The results also will aid research on traumatic brain injury, hydrocephalus, and other ailments related to increased intracranial pressure, as well as research on glaucoma and other ophthalmic diseases, NASA said.