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The eyeball lies nestled in fat within the orbital cavities (two bony sockets) of the skull, where it is situated above and lateral to the center. Of all the senses, eyesight is often considered most important. According to one estimate, four-fifths of everything we know reaches the brain through our eyes. The eyes transmit constant streams of images to the brain by electrical signals. The eyes receive information from light rays. The light rays are either absorbed or reflected. Objects that absorb all of the light rays appear black, whereas those that reflect all the light rays appear white. Colored objects absorb certain parts of the light spectrum and reflect others. When you look at something, the light rays reflected from the object enter the eye. The light is refracted by the cornea and passes through the watery aqueous humor and pupil to the lens. The iris controls the amount of light entering the eye. Then the lens focuses the light through the vitreous humor onto the retina, forming an image in reverse and upsidedown. Light-sensitive cells in the retina transmit the image to the brain by electrical signals. The brain 'sees' the image right side up.
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