http://www.stuff.co.nz/technology/gadgets/4568782/3D-makes-people-sick
Based on an unscientific, online survey, the American Optometric Association estimates that 25 per cent of Americans have experienced headaches, blurred vision, nausea or similar problems when viewing 3D.
"We do not recommend watching 3D if you are in bad physical condition, need sleep or have been drinking alcohol," the site continues.
3D screens and glasses create the illusion of depth by showing different images to each eye. That simulates the way objects that are at different distances in real life appear in slightly different places in each eye's field of view.
That's enough for most of us to perceive a scene as having depth. But our eyes also look for another depth cue in a scene:
They expect to need to focus at different distances to see sharply.
More specifically, our eyes track an approaching object by turning inward, toward our noses. Bring something close enough, and we look cross-eyed. 3D screens also elicit this response when they show something approaching the viewer.
The problem is that as the eyes turn inward, they also expect to focus closer. But a screen isn't moving closer, so the eyes have to curb their hard-wired inclination and focus back out. This mismatch between where the eyes think the focus should be and where the screen actually is forces them to work extra hard.
