Abnormal dilation or widening of the pupil. It can be caused by medications, drugs, trauma, or neurological conditions, and may be unilateral or bilateral.
From Greek 'mydriasis' meaning 'dilation,' possibly derived from 'mydros' (red-hot iron) referring to the enlarged appearance. The term has been used in medical literature since ancient Greek times to describe pupillary abnormalities.
Mydriasis can make someone look like they're perpetually surprised or frightened because their pupils are stuck wide open, unable to constrict even in bright light! This condition can be so severe that people become photophobic (light-sensitive) and need sunglasses indoors, and it's often one of the first signs emergency doctors look for in head trauma patients.
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