To look at a three-dimensional object in real life, a set of eyes must do two things. Firstly they must "verge"--rotate slightly inward or outward so that the projection of an image is always in the center of both retinas. Secondly, the eyes must "accommodate"--change the shape of each lens to focus the image on the retinas. "Without appropriate vergence, you would see double, and without appropriate accommodation, you'd see blurry," says Martin Banks, a professor of optometry at the University of California at Berkeley who is researching the effects of 3D on the visual system.
Artificial 3D causes "vergence-accommodation conflict," according to Banks, because viewers must focus at one distance (where light is emitting from the screen) but verge at another distance (wherever the 3D object appears to be in space). This difference in distance in 3D viewing may be the source of headaches and other discomforts, he says. "In 3D, the natural linkage between vergence and accommodation is broken."
Technology Review: Is 3D Bad for You?
