See 'Avatar,' Diagnose Your Vision Problems
Anyone who has yet to see the movie has probably heard five or six (thousand) times that it's best seen in IMAX or 3-D. Problem is, once they get to the theater, they might not understand what all the fuss is about, because they find they can't see 3-D but never knew.
This can cause a degree of discomfort, such as headaches, because the version of the film being seen was meant to be viewed in 3-D. And the vision problems are more widespread than one might think: 56 percent of people aged 18 to 38 have problems that could make it difficult to view 3-D properly. Another 5 percent of the population have problems that make it impossible to view in 3-D.
Apparently, however, there are therapeutic exercises that can be prescribed that enable some people to gain the ability to see in 3-D. It won't work for everyone, but perhaps the most famous instance of such exercises working is that of neuroscientist Sue Barry, who wrote Fixing My Gaze about her experiences of going from a two-dimensional to a three-dimensional world.

Others go to see Avatar and can see just fine in three dimensions, but get dizzy and feel as if they need to vomit. They're likely the same people who felt that way while watching movies such as "The Blair Witch Project" and "Cloverfield." That's called visual motion hypersensitivity and for some can be resolved through other therapeutic means.