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Its caused by the iris. The iris contains two muscles that control the siz of the pupil. The circular, or sphincter, muscle contracts in response to parasympathetic stimuli or excessive light on the retina causing a constricted or small pupil. Under the Sypathetic nervous system control, the radial muscled of the iris, when contracted, cause the pupil to dialate open. This function is easier to remember because it is associated with stress or the fight or flight response. Sypathetic stimulation leads to pupil dialation and lets us see better images. your eyes Dialate, pupils get bigger and you wont be able to read things up close for a while. it goes away after a few hours, its not painfull or anything. Its like putting eye drops in your eye.

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16y ago

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