“There is an inherent mismatch between 3D cues, says Alan Sullivan, a senior research scientist at the Mitsubishi Electric Research Laboratories in Cambridge, MA, who has worked on 3D technologies. “Your eyes must remain focused on the display, but must converge at the depth–either in front or behind the display–where the image from each eye overlaps correctly.”

Many people can view 3D without experiencing any strain at all, but Rosenberg believes that minor eye problems might be amplified slightly by watching 3D. If children experience eye strain while watching 3D, he says, “it may be an indication that they should see an ophthalmologist to see if they have an underlying problem.”

The vergence-accommodation conflict may be worse on the small screen. “As you go farther away [from the screen], the consequences of the conflict are going to be less,” says Banks. I’m not worried about the cinema situation because the distance is long.” But he recently conducted a survey suggesting that users are more likely to experience problems when they are less than a meter from a screen.

Banks’s group has developed a device designed to avoid vergence-accommodation conflict when viewing 3D. A lens in front of each eye focuses the images for the viewer to resolve the discrepancy. “Because the user’s position is known in the setup, the device can optically correct the focus accurately. In tests on 17 volunteers, users reported significantly fewer symptoms related to eye tiredness, vision clarity, and headaches than when not using the device to view 3D images. While it the setup is too cumbersome and expensive to be used for consumer products, Banks suggests that it could be used for specialized 3D applications in surgery or computer design.

Sullivan says the unconscious mental effort of reconstructing artificial 3D objects isn’t the only thing that can produce headaches and other negative symptoms. He says such problems can also be caused by mistakes in content–even small differences in sizes between the left and right images or any other kind of misalignment. “These things are easy to control with CG movies but quite hard with real scenes like football,” which has to be turned into 3D rapidly, says Sullivan. “I predict these problems will start to appear when we see 3D infomercials and low-quality content produced with less attention to detail.”