Three million to nine million people in the United States have vision problems that keep them from enjoying such 3-D movies as Avatar and Toy Story 3, estimates the American Optometric Association (AOA).
What's more, "as many as 56 percent of people between 18 and 38 years of age suffer from symptoms related to depth-perception problems." A poll conducted by the AOA found that headaches, blurred vision, and dizziness are the most common side effects from 3-D movies for people who have binocular vision difficulties.

Today's films, like those of yore, are made by recording and projecting a separate pair of image-tracks for each eye. These are slightly offset from each other, giving what's called a binocular disparity cue, which in turn produces an illusion of depth.

Vision researchers have spent many years studying the discomfort associated with watching stereoscopic movies. Similar problems plague flight simulators, head-mounted virtual-reality displays, and many other applications of 3-D technology. There's even a standard means of assessing 3-D fatigue in the lab: The "simulator sickness questionnaire" rates subjects on their experience of 16 common symptoms—including fatigue, headache, eyestrain, nausea, blurred vision, sweating, and increased salivation.

Posted in: Depth perception