CHICAGO - Our eyes are moving constantly, and it now appears this motion helps to refine and sharpen the images we see, US researchers said on Wednesday.

"It's impossible to keep your eyes perfectly still," said Michele Rucci, director of the Active Perception Laboratory in Boston University's Department of Cognitive and Neural Systems.

Rucci said researchers have long believed these rapid movements help refresh images we see, but his work shows they do something more.

"It tells us these very small eye movements, which are always there and which we almost always ignore, are rather important. They actually provide useful information," said Rucci, whose work appears in the journal Nature.

"These are very tiny eye movements. We perform them without being aware of doing so," he said in a telephone interview.

To study this phenomenon, he and colleagues asked people with good vision to report which direction an image tilted after it was briefly flashed on a computer screen.

Next, they simulated what the image would look like if the eyes were fixed, moving the image on the monitor in concert with their eyes.

"We removed the effect of these small eye movements," Rucci said.

What they found is that subjects were significantly more efficient at discriminating fine patterns when their eyes flitted around than when the image remained fixed.

He said the results explain the function of our constantly roving eyes, which may be part of a strategy used by the brain to extract useful visual information.

His work may also have some implications for people with certain eye problems, such as nystagmus, a condition characterized by involuntary eye movements that can impair vision.

"Our results may help explain the reasons behind part of these visual deficits and may contribute to the development of treatments," he said.