BSIP, CHASSENET / SCIENCE PHOTO LIBRARY BSIP, CHASSENET / SCIENCE PHOTO LIBRARY
Dilated pupil. Man with an dilated (enlarged) pupil. This effect, called mydriasis, is a normal response to dim lighting. The enlarged aperture allows more light into the eye, improving sensitivity but reducing depth of focus. It also occurs in response to adrenalin (the 'fight, fright, flight' response), sexual arousal or the use of stimulant drugs such as amphetamine. Abnormal dilation of one or both pupils sometimes results from injury to the eye or damage to the optic nerve. For the same eye with a contracted pupil, see P420/539.
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