When you watch a 3D movie there is a difference between where your eyes are focusing and the triangulation that your brain uses to perceive depth correctly. Strabismus or lazy eye is what this is called when you can’t bring both factors into alignment. Some people have trouble with this and there is concern that the new in home 3d televisions may hamper the development of these linked sense in children
Anyone who learned the technique that allows them to peer into stereograms has taught themselves a temporary form of lazy-eye. Stereograms are those pictures that look like confetti but transform into three-dimensional images if you stare into them long enough. They’re popular with college kids experimenting with Escher.
The modern digital 3D effect using glasses makes this same effect effortless. Your eyes are invited or forced not to properly focus in order to get the full effect of eye-popping 3D.
Allegedly the 3d headset that Sega was working on years ago was shelved because of this potential problem.
While going to see a 3d movie once in a while probably isn’t going to ruin your eyesight, there is concern about using the technology constantly in the home–especially use by children.