Sight for sore eyes? (Image: Ekaterina Nosenko/Getty)

Children under six should be banned from stereoscopic technology such as 3D movies, computers and video games, says France’s health and safety agency, ANSES. It is also calling for children up to 13 to moderate their use of the technology.

The call follows recommendations by the agency’s Italian counterpart last year and cites “pioneering analysis” of scientific research into the possible effect of 3D viewing on the developing visual system.

So is its recommendation reasonable? Not if it’s based on existing evidence. Crucially, the agency’s report is unclear about what exactly this “pioneering analysis” is. However, what is clear is that there is no published research, new or old, showing evidence of adverse effects from watching 3D content other than the short-term discomfort that can be experienced by children and adults alike. Despite several years of people viewing 3D content, there are no reports of long-term adverse effects at any age. On that basis alone, it seems rash to recommend these age-related bans and restrictions.


Visual concerns

Why might 3D viewing have raised concerns in the first place? The human visual system changes significantly during infancy, particularly the brain circuits that are intimately involved in perceiving the enhanced depth associated with 3D viewing technology. Development of this system slows during early childhood, but it is still changing in subtle ways into adolescence. What’s more, the visual experience an infant or young child receives affects the development of binocular circuits (Science, DOI: 10/ctvk2c). These observations mean that there should be careful monitoring of how the new technology affects young children.

Two properties of binocular vision seem to be at the heart of French concerns – vergence and accommodation – and the conflicts that arise between them with 3D viewing. These conflicts can cause discomfort. In the natural world, we shift gaze from one object to another. To look at an object means to direct both eyes to it. When the eyes are directed accurately, vergence is said to be accurate, and the viewer sees one image rather than two.

At the same time we also focus the eyes to form sharp images of the object on the retinas. Focus is adjusted by changing the curvature of the lens within each eye. We call this accommodation. When focus is accurate, retinal images are sharp; when it is inaccurate, images are blurry. Normally, vergence and accommodation are to the same distance, but in 3D viewing that is often not the case. Vergence involves the distance to the “3D” image, which could be in front of the screen or behind the screen. Accommodation remains fixed to the distance of the screen because that’s where the light actually comes from, and is where you need to focus to generate sharp retinal images.

Conflict

When vergence and accommodation distances differ in this way a conflict occurs. This is known to cause discomfort, more in some people than in others (Journal of Vision, DOI: 10/cq7h22). I know of no data, however, that show that this has long-term effects on vision. It seems that the discomfort dissipates when you stop viewing 3D content. Interestingly, the discomfort is known to be greater in adolescents and young adults than in middle-aged and elderly adults (Optometry and Vision Science, DOI: 10/xcf).

Admittedly, health risks are always possible with the introduction of new technologies and it is prudent to look carefully for adverse effects. We might not know all of the consequences of 3D technology for viewers of different ages, but there is no “smoking gun” to suggest harm is being caused. A ban for young children would be unnecessarily harsh.

Profile: Martin Banks is professor of vision science at the University of California at Berkeley