Afferent pupillary defect

The pupil (Latin pupilla "little doll" > pupa "doll") is the variable-sized, black circular or slit shaped opening in the center of the iris that regulates the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye.
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Pupil /pu·pil/ the opening in the center of the iris through which light enters the eye.pu´pillary Adie's pupil tonic p. [more]Afferent pupillary defect - Community and Resources