The Art Of Seeing - How The Eye Works: The Aging Eye Preventing And Treating Eye Disease

Content provided by the Faculty of the Harvard Medical School

The art of seeing

Sight is not fully developed at birth; the brain and eyes have to learn to work together in the first months of life. Once sight is well developed, eyes and brain team up to provide virtually instantaneous visual information.

Consider what happens when you walk through a parking lot and spot your car. First, you are not actually seeing the automobile, but rather the light reflected off it that enters your eye. There must always be some light present in order to see.

If the image is clear, it means that light thrown off every surface of the automobile hits your cornea, where it is refracted, or bent, inward and is then sent through the aqueous fluid until it reaches the lens. The light rays are then bent further, passed through the vitreous fluid, and projected onto the retina as a flat, upside-down image.

The light is absorbed by the retina and turns into electrical energy, which the optic nerve then conveys to the visual area of the brain. Data about your car — its size, shape, color, and position — are sent along the optic nerve as impulses, a sort of neurologic code that the brain deciphers. The image is actually upside down on the retina, but the brain learns to automatically turn it right side up.

Though it is possible to see with only one eye, you generally rely on binocular vision — vision with both eyes — for depth perception. You get a complete, three-dimensional view of your vehicle because the brain interprets what is seen from your two eyes (each with a slightly different perspective) as a single image.

If the flashy car nearby catches your attention, you instantly shift your gaze without a thought. The external muscles of the eyes are synchronized to keep the eyes aligned and to coordinate their movement.

Last updated:	June 19, 2007