About 5% of the global population has amblyopia that makes 3D vision impossible.
Several studies have shown that more than half of adults have binocular vision problems and therefore could have problems seeing 3D.
Many people see a two-dimensional or flat world without realizing it because they've never experienced the pleasure of seeing in 3D. Vision problems such as strabismus (crossed eyes), amblyopia (lazy eye), or poor binocular vision (eyes that turn away) can interfere with the ability to see in true 3D. To see in 3D, the eyes must work together to align the images from each eye; then the brain merges the images and converts them into a three-dimensional image.
Any movie in 3D version has two images projected on the screen, each image seen by one eye. The brain merges the images into one. If the eyes do not work together, it will be very difficult to merge the images so that it is possible to see them in 3-D.
These vision problems affect the view, beyond that to watch movies in 3D. They also affect depth perception, the ability to tell where objects are in space, eye-hand and eye-body coordination for driving and playing sports, and reading efficiency and comfort. Over time, if the eyes don't coordinate and work together, the brain ignores an image to avoid seeing double vision. This results in seeing a flat world.
But there is hope. Thanks to Dicopt 's vision therapy , people who previously couldn't see 3D are now enjoying all the special effects that 3D movies have to offer.