TWO EYES ONE IMAGE

The human visual system is a complex network including the eyes, the ocular nerves, and specific areas in the brain that process visual information. Because the eyes are side by side on the face, they see slightly different images of the same object, or the same object from slightly different perspectives, although the images overlap to some extent. These are transmitted via the optic nerve to the brain which synthesises them to create a single visual image. This ability to converge information from both eyes is called binocular vision and is essential for three-dimensional (3D) or stereoscopic vision. It allows us to perceive depth and judge distances and relationships between objects. Without it the world around us would appear flat like a two-dimensional picture.
 
So many of the day to day activities we take for granted and perform without a second thought depend on stereoscopic vision. Pouring a glass of water, parking a car, threading a needle, walking up or down stairs, catching or hitting a ball, even reaching out to shake someone's hand would be more difficult and less accurate without our ability to judge depth. It would be impossible to pursue certain professions and challenging to play certain sports.
 
The eyes and the brain need to work together in order for us to experience the world in three dimensions. The eyes are responsible for receiving a clear focused image which the brain is required to process and interpret, helping us to make sense of what we see. Light bouncing off objects passes through the cornea, and the pupil expands or contracts to control the amount of light entering the eye. It then travels through the lens and finally focuses on the retina at the back of the eye, where it is converted to electrical impulses which are sent via the optic nerve to the brain. Having gone through other areas of the brain, the impulses end up in the visual cortex where the perception of the visual images occurs. Here the brain may rely on visual memory to assist in the interpretation of the visual stimulus it has received.
 
Unfortunately, not everyone has stereoscopic vision, or the ability to see in 3D. This always occurs in people with only one functional eye and can occur to some extent in people who have two eyes that do not work together effectively. Whether someone was born with one eye or has lost an eye for whatever reason, they will be unable to perceive depth because they are unable to see an object from two different angles.
 
Binocular vision problems are among the most common visual disorders. The symptoms may include headaches, eye strain, blurred vision, light-headedness, neck and shoulder discomfort and double vision. Some people experience difficulty with balance, particularly on getting up too quickly, motion sickness and sensitivity to glare. Others may feel insecure driving as they are sometimes unable to judge the speed or distance of oncoming cars. Reading problems associated with binocular vision problems include skipping lines or words while reading, losing the place frequently, comprehension difficulties and fatigue after reading. Many people with binocular vision problems report having poor coordination especially in sports which require catching or hitting a ball.
 
Fortunately, there are a number of treatment options for most cases of binocular dysfunction. Glasses with specially prescribed lenses, filters or prisms can help to correct eye alignment. A course of vision therapy to improve eye coordination and eye teaming is generally successful. In certain cases, surgery is necessary to realign the eyes, and this may be followed by a course of vision therapy and/or the prescription of glasses. Your optometrist will guide you towards making the most appropriate decisions in terms of treatment. As with most problems, the earlier the problem is diagnosed and managed, the more successful the outcome, especially during childhood while the visual system is developing.
 
While the eyes and brain perform 3D processing automatically, film makers work at using the same principle to create movies which make the audience feel that the scenes they are watching are happening right in front of them and they are part of the action. Just as our view of the world would be flat without stereoscopic vision, so too would all the movies we see appear two dimensional on a flat screen, but more and more 3D films are being produced giving us an alternative.
 
The first 3D film was made in 1922. Since then, with the technological advances over the years, 3D movies have become extremely sophisticated and hugely popular worldwide. There are several different types of 3D technology used today to achieve a 3D image on the screen. One of these uses two cameras to film two versions of the same image to mimic the exact angle as the eyes would see it. By wearing specially designed 3D glasses, the two images taken at slightly different angles come together in a single cohesive image. Depending upon the exact type of technology used, 3D glasses will either use special shutters, color filters, or polarised lenses to receive the images. As with human vision, the final process occurs in the brain.