Mydriasis

Mydriasis /mɨˈdraɪ.əsɪs/ is a dilation of the pupil, usually defined as when having a non-physiological cause, but sometimes defined as potentially being a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment and is sometimes colloquially referred to as a "blown pupil". More generally, mydriasis refers to the dilation of pupils, for instance in low light conditions or under sympathetic stimulation. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis.