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The first three-dimensional movies came out in the 1950s, and over the past 60 years they have continually risen and fallen in popularity. With the success of Avatar in 2009, it looked like 3D would become the default for mainstream film. While 2D remains popular, many modern movies offer a 3D option, either because they were filmed specifically in 3D or were edited in post-production.

Seeing a film in 3D gives the viewer an enhanced experience, as you completely immerse yourself in the world on the screen. However, for some people, the effect is less than thrilling. Some people purchase the 3D ticket, put on the glasses, and spend the next two hours watching a flat, unfocused, two-dimensional movie, while possibly suffering from nausea or headaches.

If you can’t see movies in 3D, you aren’t alone. Around 12 percent of the population struggles with depth perception, also known as stereoblindness. For this segment of the population, 3D movies are nothing special.

Many people with stereoblindness don’t recognize the condition, since they have never seen the world in any other way. However, as you walk out of a 3D screening with your friends feeling underwhelmed, you may want to know why you see differently, how it affects your perception of the world, and if there’s anything you can do about it.

What is Stereoblindness?

Human eyes are set up so that each eye perceives a slightly different image.  The disparities between the two images are processed by the brain to provide depth perception, which allows people to gauge distances and how objects relate to each other in space.

Those with stereoblindness have eyes that are either dysfunctional or misaligned. For example, if you have a lazy eye or are cross-eyed, your eyes struggle to focus in the same direction, meaning that your brain is receiving different pictures entirely, instead of the same image perceived from two different angles.

How Does Stereoblindness Affect Your View of the World?

Those who were born with stereoblindness likely don’t realize that they see the world differently from others with stereo vision. Your mind learns to adapt to make sense of the world around you as best it can, and you can still perform most daily tasks, including driving a car in some cases, without a problem.

However, there are certain situations where lacking depth perception can be a problem. Many people with stereoblindness confess to being bad at sports that require an ability to properly see distances, such as tennis or basketball. They may also have difficultly pouring liquids into a glass or threading needles, and they likely can’t become a pilot or surgeon because these jobs require strong depth perception.

Of course, the most readily noticeable side effect of stereoblindness is the inability to see 3D movies, games, or pictures.

How Do 3D Films Work?

Three-dimensional films work by tricking your eyes into thinking they’re staring at an object with depth, not a flat screen. Movies filmed in 3D are usually shot by two cameras, placed at about the same distance apart as human eyes. The two images are then superimposed on each other, mimicking the process of stereo vision in the brain.

If you look at a 3D film, or other form of media, without any additional instruments, the image looks flat and blurry, which is why you need a pair of 3D glasses. Older 3D films relied on color systems to achieve the 3D effect. One camera would have a blue filter, and the other a red filter, and the audience would receive a pair of 3D glasses with one blue lens and one red lens. The different colors mimic the image disparity of looking at real-world objects, which creates a sense of depth.

Modern 3D entertainment relies on polarization, not color. One lens of the polarized glasses views vertical light waves, while the other views horizontal light waves.  Again, the image disparity between the right eye and light eye mimics real vision, making the flat image on the screen appear to have depth.

If you have stereoblindness, you can’t see the slight image disparity in the first place, so putting on the glasses simply brings the movie into focus, while remaining flat.

Can You Cure Stereoblindness?

The possibility of treatment depends on what causes your stereoblindness, how long you’ve had it, and how severe it is. Children born with lazy eyes or crossed eyes can receive surgery to strengthen the muscles and hopefully bring the eyes back into alignment, but this doesn’t always work, and probably won’t help adults who have been stereoblind for years.

There isn’t one solid technique used to treat stereoblindness, nor do experts have a way to predict with 100 percent certainty that a technique would work. Some doctors recommend surgery, regardless of age, while others find vision therapy helpful. Neuroscientist Susan Barry, who had been stereoblind her whole life, practiced eye exercises to train herself to see depth and successfully developed stereo vision.

For at least one person, psychology professor Bruce Bridgeman, watching a 3D movie actually corrected his stereoblindness. It’s not a scientifically proven cure, and might not even work for another person, but it might give you a good reason to go to the newest 3D movie with your friends—just in case.

If you’re comfortable with your current sight, it’s possible to live a complete and fulfilling life without striving for stereo vision. However, if you want to try and understand what all this 3D hype is about, visit All About Eyes for a comprehensive eye exam and some expert advice.

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