3-D movies are becoming more and more popular. Mainly because it gives you the feeling that you are actually in the movie, or maybe that the movie is in your life. But why do you need those goofy over sized glasses? How does 3-D work?
Unlike the eyes of the space aliens featured in some 3-D features, our two eyes are not positioned together, but lie approximately 3 inches apart. This separation causes each eye to see the world slightly differently. The brain fuses these two views together and uses them to calculate distance, creating our sense of depth.
In other words it makes the images that we see appear to be real and allows us to understand the amount of space that an object takes up.
3-D glasses work similarly, feeding different images into your eyes (thus the two different-colored lenses: one red, one blue). In a theater, the movie screen actually displays two images, and the glasses cause one of the images to enter one eye and the second image to enter the other.
Binocular Depth Perception
It may surprise you to learn that the ability to visually perceive three-dimensional space, called “binocular depth perception,” can be achieved without external aid. In fact, this ability is a way to measure parts of our vision: if you can successfully combine separate images from two eyes into one three-dimensional image in your brain, your binocular vision is working well.
Both eyes are working as a team.
Yet not all people have binocular depth perception. According to the Optometrists Network, up to 12 percent of the population has some type of binocular vision disability: the two most commonly known types are amblyopia and strabismus.
Amblyopia, from the Greek word amblys, meaning “blunt” or “dull,” is a condition in which one eye has lowered visual acuity and/or poor muscle control. Your eyes may be straight, but one eye doesn’t send the proper information to the brain, so your brain can’t perceive binocular depth. Amblyopia – more commonly known as “lazy eye” – affects approximately 2 or 3 out of every 100 children in the United States.
This condition may affect one or both of the eyes. The affected eye sends a blurry image to the visual cortex. The visual cortex is the part of the brain that that is used for detailed or critical seeing. This condition normally develops in childhood and is actually a neurological condition rather than an eye function issue. Even with corrective lenses the brain continues to receive a blurred image from the affected eye.
Conversely, strabismus, from the Greek word for “squint,” is a visual defect in which you may see clearly, but your eyes don’t line up – the two eyes point in different directions. One eye may turn in, out, up, or down, while the other eye looks straight ahead. That’s why strabismus is more commonly known as “walleye” or “wandering eye.” Strabismus affects approximately 4 out of every 100 children in the United States.
Besides the visible problems of the eyes not aligning properly, people suffering from strabismus may also be experiencing double vision. Many people believe that this condition is caused by weak muscles in the eyes. The problem is more complex than that. This condition is caused by the eye and the brain actually getting their signals crossed.
These conditions are not always easy to diagnose. With strabismus, particularly, the eye mis-alignments may not be obvious to the untrained observer unless it is severe. And it used to be that doctors thought lazy eye could only be treated in childhood, up to about 8 years old. Currently, treatment is given at any age.
Before starting any kind of eye treatment you should talk to your eye doctor.
In severe cases of strabismus it may be necessary to have surgery to correct the eyes alignment. However, in less severe cases you may be able to use eye exercises to correct or retrain the muscles in your eyes.
If you chose surgery to correct this problem be sure to talk to your vision specialist about orthoptics and treatment for any vision issues that are caused by the condition. Surgery is the fastest way to achieve a cosmetic change, but without proper treatment of visual problems associated with the condition, it only solves half of the problem.
Eye exercises, or orthoptics, may also be a good option to consider when treating amblyopia. Your ophthalmologist may even suggest that you use a patch over your good eye in order to train the lazy eye to function correctly. They may also recommend corrective lenses. Another newer form of treatment for this condition includes the use of special eye drops that produce a blurred image from the strong eye.
When the brain is receiving blurred images from both eyes it learns to interpret the information it receives correctly. The best results may combine a combination of eye patch, eye drops, and exercises designed to help the brain understand the images it is receiving.
So next time you’re watching a 3-D production, give your eyes a screening, too. You can test your binocular depth perception by first covering and then uncovering one eye: if the image floats out from the screen, your eyes are working in tandem. If the image remains flat, you may have a vision problem, so consult your ophthalmologist.
And if you see any space monsters coming for you, duck.