Published: 6 October, 1999

Eyes work together to produce 3-D images

How come we have two eyes but see only one of everything?

Although we see with two eyes, we do not see double images. The muscles that control our eyes work automatically to focus both eyes on the same spot. The image of an object is focused on corresponding points of the retina for each eye. (The retina is located at the inner back surface of the eyeball and serves a purpose similar to that of film in a camera.) Nerve impulses sent to the brain from light falling on the retina result in a single image.

When a person has two eyes that do not track together correctly, crossed eyes result and double vision becomes a problem. An eye with poor vision can become 'lazy' and not track with the good eye. Then the image of an object is formed at non-corresponding points on the retinas of the two eyeballs, and nerve impulses sent to the brain are interpreted as two different images.

By having two eyes, we do see a single scene or object from two slightly different angles. This gives depth to a scene and we see in three dimensions. A View-Master viewer works with the same principle by having two photos of the same scene. Each photo alone shows a flat, two-dimensional picture but one photo shows a little more of the scene on the right and less on the left and the other photo reverses the process. When both photos are viewed simultaneously by a pair of eyes, the three dimensional aspect is restored.