A few days ago I found an odd package waiting in my mailbox. One of the commercial TV networks got my postie to deliver a pair of 3D glasses - very old school, with separate red and blue lenses. I spent a few moments assembling them, and presto! I looked like I'd just walked out of a showing of 1954's Creature From the Black Lagoon.

Now that James Cameron's Avatar has become the highest-grossing film in history, 3D is very hot. The hottest new toys unveiled at this year's Consumer Electronics Show were 3D television sets, 3D Blu-Ray players, and comfortable 3D glasses for the lounge room. At least three US-based cable networks have promised 3D broadcasts will begin sometime this year - for the few people who have 3D television sets. Everyone in the consumer electronics industry sees this as the Next Big Thing: now that everyone has purchased big, flat-screen TVs, 3D is the next logical step, the necessary upgrade that keeps us all on the treadmill of progress. The movie studios have also gotten behind 3D in a big way. Just last week Warner Brothers announced that the two final Harry Potter films will be shot in 3D.

Is this the decade of 3D? It might look that way, but we'd all better hope it turns out quite differently. You see, 3D is not good for you.

How can this be? Isn't the real world in 3D? Yes, the real world of objects is definitely three-dimensional. But that's where the similarity ends. What you're shown on a movie screen - or soon, a television - is not true 3D. That's the source of the problem.

Back in the 1990s I did a lot of development work in virtual reality - another technology destined to be the Next Big Thing. I helped Sega develop a head-mounted display (fancy VR headgear) that could be plugged into the Sega Genesis (known as the Mega Drive in Australia). Everything was going swimmingly, until we sent our prototype units out for testing.

Virtual reality headsets use the same technique for displaying 3D as we find in movies or 3D television sets - parallax. They project a slightly different image to each one of your eyes, and from that difference, your brain creates the illusion of depth. That sounds fine, until you realize just how complicated human depth perception really is. The Wikipedia entry on depth perception (an excellent read) lists ten different cues that your brain uses to figure out exactly how far away something is. Parallax is just one of them. Since the various movie and television display technologies only offer parallax-based depth cues, your brain basically has to ignore several other cues while you're immersed in the world of Avatar. This is why the 3D of films doesn't feel quite right. Basically, you're fighting with your own brain, which is getting a bit confused. It's got some cues to give it a sense of depth, but it's missing others. Eventually your brain just starts ignoring the other cues.

That's the problem. When the movie's over, and you take your glasses off, your brain is still ignoring all those depth perception cues. It'll come back to normal, eventually. Some people will snap right back. In others, it might take a few hours. This condition, known as 'binocular dysphoria', is the price you pay for cheating your brain into believing the illusion of 3D. Until someone invents some other form of 3D projection (many have tried, no one has really succeeded), binocular dysphoria will be part of the experience.

This doesn't matter too much if you're going to see a movie in the theatre - though it could lead to a few prangs in the parking lot afterward - but it does matter hugely if it's something you'll be exposed to for hours a day, every day, via your television set. Your brain is likely to become so confused about depth cues that you'll be suffering from a persistent form of binocular dysphoria. That's what the testers told Sega, and that's why the Sega VR system - which had been announced with great fanfare - never made it to market.

Video games are one of the great distractions of youth. Children can play them for hours every day, and our testers realized that children - with their highly malleable nervous systems - could potentially suffer permanent damage from regular and extensive exposure to a system which created binocular dysphoria in its users. This is the heart of my concern, because 3D television is being pitched as an educational medium - Discovery Channel has announced 3D broadcasts will begin mid-year - and that medium could damage the growing minds it is intended to enlighten.

All of this is rolling forward without any thought to the potential health hazards of continuous, long-term exposure to 3D. None of the television manufacturers have done any health & safety testing around this. They must believe that if it's safe enough for the cinema, it's fine for the living room. But that's simply not the case. Getting a few hours every few weeks is nothing like getting a few hours, every single day.

One of two things is about to happen: either 3D television will quickly and quietly disappear from the market, from product announcements, and from broadcast plans, or we'll soon see the biggest class-action lawsuit in the planet's history, as millions of children around the world realize that their televisions permanently ruined their depth perception. Let's hope 3D in the home dies a quiet death.