TORONTO -- Patching has long been used to treat a lazy eye in children, although the therapy has limited success and doesn't work at all in adults with the condition formally known as amblyopia.

Now researchers at McGill University in Montreal are testing an innovative means of improving visual function in adults with lazy eye -- a puzzle video game that forces both eyes to work together to overcome the common condition.

In a study published Monday in the journal Current Biology, the researchers compared the use of the online video game Tetris with patching, a treatment in which the "good" eye is covered for a lengthy period of time. The idea is to make the weak eye do all the visual work in the hope of strengthening its acuity.

The patients treated using Tetris showed a four-fold improvement in vision in their lazy eye compared with those who were patched, said ophthalmologist Dr. Robert Hess, director of McGill's vision research unit and principal investigator of the study.

Tetris is an early video game that involves manipulating shapes made of small squares -- moving them side-to-side or rotating them -- as they fall to the bottom of a background grid of same-sized squares. The goal is to connect different shaped blocks, putting them together in an integrated whole before they fall to the bottom.

"The game itself is sort of incidental in a way," Hess explained Monday from Montreal. "It just provides us with a platform to administer this training that we need to do in a way that's enjoyable.

"The game itself is not so important as the principle behind how we manipulate the game to do some good."

About three to four per cent of the population develops a lazy eye in very early childhood, making it the most common cause of vision problems in children. A lazy eye, which is unable to see details in sharp focus, has a number of causes, including having misaligned eyes (being cross-eyed) or having a congenital cataract that clouds the lens.

The eye itself is usually otherwise normal, as is the optic nerve that transfers visual information to the brain. The problem is with the brain's visual cortex, which has learned to suppress the information from the weak eye in favour of the other eye, leading to single-eye or monocular vision.

"We know the eye itself is fine; we know it's all in the brain," said Hess. "We're now beginning to realize that it's just the software that's gone wrong."

Typically, people with amblyopia also have little or no 3D vision, because it takes both eyes working together to provide depth of vision.

"It looks flat and boring. If you ever try walking around with a patch over one eye, the world looks miserable," Hess said of having inadequate three-dimensional depth of field.

"It's getting the brain to get out of this learned suppressive mode that we're trying to do with this game."

In the study of 18 adults with amblyopia, half played the game Tetris an hour a day for about six weeks, while the other half had a patch put over their good eye and played the game with just their bad eye.

For the first group, the idea was to make the lazy eye focus on the falling shapes, which the researchers made high contrast, and to have the dominant eye focus only on the background grid, which was rendered in low contrast.

"Using head-mounted video goggles, we were able to display the game dichoptically, where one eye was allowed to see only the falling objects and the other eye was allowed to see only the ground-plane objects," said Hess.

"And it turns out the more they do that, the more the two eyes work together for the first time ever for them, the stronger it becomes and the more we can increase the contrast in the good eye, higher and higher, and bring it all the way up so the contrast is the same.

"We know they're doing it because they're playing a video game, where to increase the contrast, they need to get a good score. And to get a good score, they need to have combined the information in two eyes."

Hess believes binocular training like this should become standard treatment for adults with amblyopia. McGill holds a patent on the technique and hopes to commercialize it for use by health professionals.

The game-based procedure also is being tested in children by researchers at the Retina Foundation in Dallas, Texas, one part of a worldwide clinical trial that will compare the video game technique against patching to see which is superior.

Finding a treatment other than patching the stronger eye would be a huge step in dealing with amblyopia, Hess said.

"It's hated. It's universally hated because kids firstly don't want to be condemned to the poor vision of their amblyotic eye. They don't want to be teased. And it's annoying to have on," he said, noting that some kids are told they need to wear an eye patch for months or even years.

"So there's lots of psychological and social reasons that have led to a low compliance."

In any case, patching is no panacea, even for kids, whose brains have more plasticity than those of adults, he said.

"It does improve vision a little bit in the younger age group, but it's never been as successful as it should be."