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On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 6 October, 1999 Next Week's Question
Eyes work together to produce 3-D images
Question
How come we have two eyes but see only one of everything?

Question
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.

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