Mind Games: Tetris as a Tool for Neuroscience #3

tetris

From Penicillin to Pulsars, sometimes great discoveries come from the most unlikely of sources. Here are three neat little advances in neuroscience that are thanks to a clunky, classic videogame – Tetris

 

Part Three: Treating Lazy Eye

 

It’s a popular white lie to children that TV and computer screens will give you square eyes so that you need glasses. But now it seems that technology could actually be used to improve vision – such as correcting lazy eye.
Lazy eye, or Amblyopia, is the chronic blurring of vision in one eye, which cannot be corrected with glasses or contacts. Sometimes, the eye is also misaligned. Having poor vision in one eye also means that binocular vision – the ability of the eyes to work together – is also affected.

 

Normally, the eyes aim at the same object of interest, and send this image to the brain. As the eyes are in different positions, they have a unique perspective on the object and send two slightly different images to the brain, which must combine the images into one. This resulting image is three-dimensional due to this slight difference in perspective, and it is this image that allows us to perceive depth. For the person with Amblyopia however, the image from the lazy eye is too poor to be integrated, so depth perception is sketchy or even non-existent.

 

Lazy eye is conventionally treated by placing a patch over the working eye, to force the lazy eye to try harder, improving its power. But patching isn’t perfect. For one thing, its usually only effective in children under 12, as the adult visual system is assumed to be too rigid for any vision to recover. The child undergoing patching will need to cope with poor vision during treatment, and at a self-conscious age, the potential embarrassment of wearing a patch for months is likely to lead to poor compliance. There is also the risk of causing reverse Amblyopia, whereby the previously working eye then becomes lazy due to lack of use. Even if patching is successful in improving vision in the lazy eye, binocular vision may not be restored. For Robert Hess, a vision researcher at McGill University, Montreal, a better solution, which might also work for adults, was needed.

 

The predominant way of thinking about lazy eye is that the loss of binocular vision is a by-product of the loss of vision in the lazy eye. But, as Hess reasoned, perhaps the reverse were true. Perhaps the problem is in the brain, not the eye, so that the lazy eye’s lack of vision is a result of a failure of the brain to allow the eyes to work together – one eye then dominates, causing the surplus lazy eye to give up in an efficiency drive. If true, getting the eyes to work together should improve the lazy eye’s functioning when tested on its own.

 

From Hess’ perspective, lazy eye persists not because the cells that would pick up visual information from this eye die off or never fully develop, but because their activity is suppressed by the inputs from the other eye to the brain. This fits with research showing that people can not only see with their lazy eye but combine information from both their eyes if the visual picture is altered so that the working eye is no longer at an advantage. It would seem that the mechanisms for binocular vision were preserved in people with lazy eye, but they were not being used, perhaps because these mechanisms were being suppressed by the more functional tissues of the working eye.

 

With this in mind, Hess and his team developed a task that could only be completed if the eyes worked together – Tetris, but with a twist. In this version of the game, each eye only saw a part of the picture. The working eye only saw the Tetris blocks that were accumulating on the ground, whilst the lazy eye only saw the falling blocks which needed to be fitted into the blocks on the ground. In another version, the falling shapes were actually split between the eyes, so that both eyes needed to view the image in stereo to work out which shape they were seeing. This also provided a reference marker for the brain to line up the two images in the right place. In both versions, the lazy eye’s image was presented at a higher contrast than the working eye’s image, to remove the working eye’s advantage and lessen the brain’s suppression of input from the lazy eye.

 

The idea behind this was that, with practice, the eyes would start to work together with smaller and smaller differences in contrast, in line with other research, until eventually, stereo vision could be achieved in everyday life. Ergo, the exact contrasts required were different for each person undergoing the Tetris treatment.

 

To put the treatment to the test, Hess and colleagues recruited nine volunteers with lazy eye, who then played the modified Tetris game for around an hour each day. The volunteers varied in the severity of their lazy eye, but most of them had no depth perception whatsoever. Over a week of training, the contrast difference needed to play Tetris reduced dramatically for the volunteers, and the researchers noted substantial improvements in the ability of their lazy eyes to pick out details, such as letters of the alphabet. For around half of the volunteers, depth perception also improved, suggesting that the necessary neural capability for depth perception had been preserved, even though it was not being used.

 

Whilst Tetris seems a much more appealing (and less embarrassing) treatment than a patch, it has the added benefit of allowing opticians to test the severity of Amblyopia by checking the amount of contrast required for the lazy eye to see clearly. The researchers definitely deserve credit for thinking outside the blocks…

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