3D May Be Unhealthy
By forcing the eyes to focus on things at varying distances, 3D can cause a problem called vergence accommodation conflict. Explained Martin Banks, professor of optometry: "You have to concentrate your eyes to something near, but focus your eyes on something far. So you have to break that normal coupling between avergence and accommodation." See Voice of America.
There may also be a hygiene risk. The Italian ministry of health says that reused 3D glasses may cause outbreaks of herpes on the forehead. The ministry confiscated 7000 pairs of 3D glasses from theaters, including the Vatican IMAX theater. Some speculate that the move came suspiciously soon after the announcement that softcore filmmaker Tinto Brasso would undertake a racy remake of Caligula. See Movieline.