A mission with dozens of animals launched into space in a Russian satellite yielded clues to why astronauts' eyesight deteriorates in space, scientists say.

The experiment showed the capacity of the cerebral arteries was diminished in space, which accounts for the effect on vision, Vladimir Sychev of Russia's Institute of Medical and Biological Studies said.

"We used to think that in zero-gravity, fluid traveled upward and that the quality of [blood] improved, but it turns out that it is the other way around," Sychev told RIA Novosti. "The arteries of the brain come under duress and their capacity is reduced by 40 percent."

The "space ark" mission yielded useful information on the impact of space travel on the spinal cord, inner ear and processes at the genetic level, Sychev said.

Russia launched the Bion-1M satellite with its cargo of creatures on a 30-day mission in April to conduct research on changes to the body while in orbit.

Mice, geckos, gerbils, slugs and snails were onboard, along with containers of microorganisms and plants.

The mission was considered a success although few of the animals in the satellite returned from orbit alive, Sychev said.