Many of the tabloid scares have quoted professor Martin Banks, head of the University of California Berkley Visual Space Perception Laboratory, but his tone is very different to the papers'.
"There are some issues to worry about, but in my opinion the most plausible ones concern people feeling bad, not having their health somehow adversely affected," he told us. Banks argues that the way we focus on 3D images can, in some cases, cause discomfort to people using 3D screens.
"The issue we know the most about is the so-called vergence-accommodation effect. Vergence is the way we direct our eyes to fixate a point in space. We converge our eyes to look at something near and diverge to see something far. Accommodation is the focusing response of the eyes. We change the shape of the lens inside the eye to bring images into sharp focus on the retinas."
With 3D, we're asking our eyes and brains to do strange things. "In the real world, the distances to which the eyes must converge and accommodate are the same, so those responses are coupled in the brain," Banks says.
"With stereo 3D displays (S3D), the eyes must converge to the distance of the content (sometimes in front of the screen, sometimes at the screen, sometimes behind) while always focusing at the screen where the light is coming from. This requires the brain to converge and accommodate at two different distances, and this is known to cause some discomfort, fatigue, and occasionally headache."
The good news is that not everybody suffers from the problem of eye strain. The bad news is that the younger you are and the closer to the screen you are, the more likely you are to encounter an issue.
"The problem decreases with age such that it's not an issue with 50-year olds or older," says Banks. "The problem also decreases with viewing distance. Thus, video gaming is indeed a prime target for problems due to this conflict because the viewing distance is short and the typical user is young."
Lying eyes
Dr Stephen Hicks of Oxford University's Department of Clinical Neurosciences thinks that any permanent effects are highly unlikely.
"Permanent changes to the visual system are very difficult to make," he says. For example, "Squint and amblyopia are common deficits in vision in children, where a weaker eye disrupts ordinary binocular vision. A common treatment is to patch the strong eye in order to encourage greater strength in the weaker one. This can require several hours of patching per day, sometimes for several months. This is a dedicated process that corrects a very slight defect - to produce an irregular mode of sight is likely to take orders of magnitude longer, and still may have no permanent effect."
Dr Hicks describes a well-known visual experiment, the inverted vision experiment, where "people discovered that if you put glasses on that flip the world upside down, you find things very difficult to do at first - but after a day or so, people report that the world seems the right way up again. The brain recodes the visual information to keep it in sync with your body and environment. When you take the glasses off, the world is again upside down and takes a short time - this time only about an hour or so - to correct itself."
As Dr Hicks explains, with 3D, "this suggests that any temporary changes that occur to your visual system as it adapts to even regular 3D movie or TV watching will be rapidly reset by a short period in the real world."
What about gaming, where a suitably involving game can keep you engrossed and immediately in front of a 3D screen for long periods? "It's possible that after several hours of exposure, the sense of depth will be slightly inaccurate. The difference here is that a video game is a consistent single point of view; there is rarely much editing and as such the effect is stronger, but also less fatiguing."
Our own anecdotal experiences of 3D suggest that there is some difference between two- and three-dimensional entertainment: we've found 3D quite tiring for adults and children alike, especially when it's 3D of the fast-edit, look-it's-coming-right-at-you variety.
"Many people have outlined reasons why 3D is more tiring than 2D, from poor quality glasses with grubby plastic, to lower light levels caused by polarised lenses, or the discord between apparent depth and focus - everything is in focus in 3D - but the arguments I find most convincing refer to the poor use of 3D by film-makers themselves,"
Dr Hicks says. "Every time we see a new 3D scene, we may be forced to reinterpret the world's depth. This can be exhausting if the director has chosen rapid edits, as they often do, which are tiring for children without the added burden of altered visual convergence."
It's not technology, but the way it's used - which explains why subtle 3D like that used in Toy Story 3 isn't as tiring to watch as an action film that's been given a speedy 3D makeover in postproduction.
"Over time this will be improved at the cinema," Dr Hicks predicts, "but I don't see 3D TV ever becoming consistent in depth. Think about what happens when a 3D ad comes on, and all of a sudden things are flying around in all sorts of eye-popping ways."
Thumbs up for 3D?
Rather than ruining our eyes, it seems that 3D might in fact be a useful tool for optometrists. That's the position of the American Optometric Association, which suggests that "3D viewing may actually help uncover subtle disorders that, left uncorrected, often result in learning difficulties."
"In this context," the AOA says, "it is not enough to have 20/20 visual acuity. Eye muscles must be co-ordinated well enough to experience single, clear and comfortable vision by maintaining alignment of both eyes. The brain must also match appropriate accommodative or focusing power with where the eyes are aimed. Often, subtle problems with these skills can lead to rapid fatigue of the eyes and loss of 3D viewing, but also loss of place when reading or copying, reduced reading comprehension, poor grades and increased frustration at school. Difficulties with appreciating 3D in movies, TV and Nintendo's 3DS, or discomfort when engaging in these activities, may be an important sign of undetected vision disorders."
That doesn't mean 3D is an unalloyed delight for young children. Optical experts and 3D manufacturers warn that children aged six or under shouldn't watch 3D content for long periods. The concern is that developing eye muscles may be susceptible to problems, and while there's no evidence that 3D does any damage to children's eyes - "studies on the effects of prolonged 3D viewing on young children remain to be done," the AOA admits.
As Dr Hicks points out, it's very difficult to make even a minor change to eyesight - the precautionary principle says that until more research has been carried out, it's better to be safe than sorry. It's unlikely that 3D will create eye problems in children, but it's possible that it could aggravate some existing conditions.
The eyes have it
"We don't know enough about the effect of age to make strong recommendations," Professor Banks says. "I'd suggest that you and others pay attention to how their kids are feeling and act accordingly."
In particular, parents should watch out for what the AOA calls "the three Ds of 3D" - discomfort, dizziness or lack of depth perception. If a child appears to be having difficulties with a 3D display, it's time to consult an eye expert - the sooner the better.
"Although success can be attained in treating conditions such as amblyopia (lazy eye) and strabismus (eye turn) beyond age six, the outcome is always better when children are treated as soon as signs of these problems are detected," the AOA recommends.
Variations in eyesight mean that for some people, 3D will never deliver a happy experience, but 3D is just the messenger, highlighting flaws that weren't apparent before. Nobody's brain is being rewired.
"Don't worry about brains," Dr Hicks says. "They're resilient, flexible and will always come back to the natural world." And turning up the 3D effect on a 3DS, wearing RealD glasses in the cinema or slumping in front of Sky 3D won't damage your eyes.
Like any other technology, 3D is fine in moderation, but overdo it and bits of you will start to complain.
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First published in PC Plus Issue 310
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