The study by The Eyecare Trust (via Eurogamer) finds that "more than one in ten of [UK residents] (12%) has a visual impairment that means our brains are unable to correctly process the individual images that are transmitted to it via our left and right eyes," leading to an "inconsistency in viewing the three spatial dimensions (height, width and depth) required to enjoy 3-D films."
If you cannot see the effect of stereoscopic 3D or get headaches during viewing, it could mean you have poor binocular vision. The Eyecare Trust recommends that you "pop along to your local optician for a sight test." The findings might not be unbiased as this establishment exists to "raise awareness of all aspects of eye health and the importance of regular eyecare" and probably has a vested interest in encouraging people to visit the doctor.
I, personally, have problems with stereoscopic 3D. I get headaches after a bit of viewing. If these conclusions are valid, it could mean that around 30 million people in the US could be affected. Take the results with a shaker of salt, but people have been experiencing problems.