Astronauts spending as little as 2 weeks in space may experience profound changes in eye structure and gene expression, U.S. researchers report.

A study of how low gravity and radiation and oxidative damage affected mice kept on the International Space Station examined eye-related gene expression and cell behavior after spaceflight, they said.

Researchers from Houston Methodist, NASA's Johnson Space Center and two other institutions reported their results in the journal Gravitational and Space Research.

"We found many changes in the expression of genes that help cells cope with oxidative stress in the retina, possibly caused by radiation exposure," Houston Methodist pathologist Patricia Chevez-Barrios, said.

Studies since 2001 have suggested astronauts are at increased risk of developing eye problems like premature age-related macular degeneration. High-energy radiation from the sun can cause damaging chemical reactions in cells, collectively called oxidative stress, and while Earth's atmosphere protects people on the ground, there's no such protection for astronauts.

Some changes in eye structure noted in the study "were partially reversible upon return to Earth," Chevez-Barrios said, but some optic nerve changes consistent with mechanical injury "did not resolve."

"And we saw changes in the expression of DNA damage repair genes and in apoptotic pathways, which help the body destroy cells that are irreparably damaged."

"We think our results are plausible based on what we know from previous studies of structural changes and damage caused by oxidative stress and changes in the eyes of astronauts returning to Earth, but additional experiments are needed to confirm what we are reporting about gene expression, cellular behavior and mechanisms of damage," she said.