<Tr> <Th> MeSH </Th> <Td> D015878 </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> Mydriasis (/ mɪˈdraɪ. əsɪs /) is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response . Non-physiological causes of mydriasis include disease, trauma, or the use of drugs . </P> <P> Normally, as part of the pupillary light reflex, 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 . The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis . More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation . </P>

An agent that causes the pupil to dilate is called