[top photo: Screenshot of video game Call of Duty 2]

CHICAGO (Reuters) - Adults who play a lot of action video games may be improving their eyesight, U.S. researchers said on Sunday.

They said people who used a video-game training program saw significant improvements in their ability to notice subtle differences in shades of gray, a finding that may help people who have trouble with night driving.

"Normally, improving contrast sensitivity means getting glasses or eye surgery -- somehow changing the optics of the eye," said Daphne Bavelier of the University of Rochester in New York, whose study appears in the journal Nature Neuroscience.

"But we've found that action video games train the brain to process the existing visual information more efficiently, and the improvements last for months after game play stopped."

For the study, the team divided 22 students into two groups. One group played the action games "Call of Duty 2" by Activision Blizzard Inc and Epic Games' "Unreal Tournament 2004." A second played Electronic Arts Inc's "The Sims 2," a game they said does not require as much hand-eye coordination.

The two groups played 50 hours of their assigned games over the course of nine weeks. At the end of the training, the action game players showed an average of 43 percent improvement in their ability to discern close shades of gray, while the Sims players showed none.

Bavelier found very practiced action gamers became 58 percent better at perceiving fine differences in contrast.

"When people play action games, they're changing the brain's pathway responsible for visual processing. These games push the human visual system to the limits and the brain adapts to it," Bavelier said in a statement.

She said the findings show that action video-game training may be a useful complement to eye-correction techniques.

(Editing by Mohammad Zargham)