The Pupil

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An interactive Flash diagram of the pupil, and the part it plays in the human eye. When light enters the eye, the iris around the pupil uses its two muscles (the sphincter pupillae and the dilator papillae) to change the size of the iris, and the amount of light it receives—a change in light level causes both pupils to react the same way, regardless if only one eye is affected by the light. Observe this reaction by using a virtual flashlight, or click through a slideshow and roll-over individual segments to learn about these parts of the pupil, and their specific functions.