pupillary reflex n the contraction of the pupil in response to light entering the eye
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the reflex change in the size of the pupil according to the amount of light entering the eye. Bright light reaching the retina stimulates nerves of the parasympathetic nervous system, which cause the pupil to contract. In dim light the pupil opens, due to stimulation of the sympathetic nervous system. See also iris.
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1. contraction of the pupil on exposure of the retina to light. Called also light r. and pupillary light r. 2. any reflex involving the iris, changing the size of the pupil in response to a stimulus, e.g., change in illumination, change in point of fixation, sudden loud noise, or emotional stimulus.Medical dictionary. 2011.