Editing Pupil (section)

==Clinical significance==
{{further|Pupillary response}}

===Effect of drugs===
If the drug pilocarpine is administered, the pupils will constrict and accommodation is increased due to the parasympathetic action on the circular muscle fibers, conversely, atropine will cause paralysis of accommodation (cycloplegia) and dilation of the pupil.

Certain drugs cause constriction of the pupils, such as [[opioids]].<ref>{{Cite journal|last=Larson|first=Merlin D.|date=2008-06-01|title=Mechanism of opioid-induced pupillary effects|journal=Clinical Neurophysiology|volume=119|issue=6|pages=1358–64|doi=10.1016/j.clinph.2008.01.106 |pmid=18397839|s2cid=9591926}}</ref> Other drugs, such as [[atropine]], [[LSD]], [[MDMA]], [[mescaline]], [[psilocybin mushrooms]], [[cocaine]] and [[amphetamines]] may cause pupil dilation.<ref>{{Cite journal|url=https://www.csam-asam.org/sites/default/files/pdf/misc/Howtospot.pdf|title=How to spot illicit drug abuse in your patients|last=Johnson|first=Michael D.|date=October 1, 1999|journal=Postgraduate Medicine|volume=106|issue=4|pages=199–200, 203–6, 211–4 passim|doi=10.3810/pgm.1999.10.1.721|pmid=10533519|access-date=March 22, 2018}}</ref><ref>{{Cite journal|last1=Alderman|first1=Elizabeth M.|last2=Schwartz|first2=Brian|date=1997-06-01|title=Substances of Abuse|url=https://pedsinreview.aappublications.org/content/18/6/204|journal=Pediatrics in Review |volume=18|issue=6|pages=204–215|doi=10.1542/pir.18-6-204 |s2cid=73382801 }}</ref>

The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation.  In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited.  The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle.

Another term for the constriction of the pupil is [[miosis]]. Substances that cause miosis are described as miotic.  Dilation of the pupil is [[mydriasis]].  Dilation can be caused by mydriatic substances such as an eye drop solution containing [[tropicamide]].

=== Diseases ===
A condition called ''bene dilitatism'' occurs when the optic nerves are partially damaged.  This condition is typified by chronically widened pupils due to the decreased ability of the optic nerves to respond to light.  In normal lighting, people affected by this condition normally have dilated pupils, and bright lighting can cause pain.  At the other end of the spectrum, people with this condition have trouble seeing in darkness.  It is necessary for these people to be especially careful when driving at night due to their inability to see objects in their full perspective.  This condition is not otherwise dangerous.

=== Size {{anchor|Diameter}} ===
{{Main|Mydriasis|Miosis|Pupillary response}}
The size of the pupil (often measured as [[diameter]]) can vary between 8 and 1.5&nbsp;mm.<ref name=":1">{{Cite journal |last=McDougal |first=David H. |last2=Gamlin |first2=Paul D. |year=2015 |title=Autonomic Control of the Eye |journal=Comprehensive Physiology |volume=5 |pages=439–473 |doi=10.1002/cphy.c140014|pmc=4919817 }}</ref> Pupil size can be a [[symptom]] of an underlying disease. Dilation of the pupil is known as [[mydriasis]] and contraction as [[miosis]].
[[File:Voluntary pupil dilation.gif|thumb|A human adult exhibiting voluntary control over his iris muscles, which grants him the ability to dilate and constrict his pupils on command]][[File:Human eye in dim light.jpg|thumb|260x260px|Pupil dilated naturally to 9 mm due to dim light. The subject is an extreme case, as most individuals are not able to naturally dilate their pupils to that extent]]
[[File:Human eye in bright light.jpg|thumb|260x260px|Pupil constriction can be in response to negative emotional states]]
Not all variations in size are indicative of disease however. In addition to dilation and contraction caused by light and darkness, it has been shown that solving simple multiplication problems affects the size of the pupil.<ref>{{Cite journal|last1=Hess|first1=Eckhard H.|last2=Polt|first2=James M.|date=1964-03-13|title=Pupil Size in Relation to Mental Activity during Simple Problem-Solving|journal=Science |volume=143|issue=3611|pages=1190–2|doi=10.1126/science.143.3611.1190 |pmid=17833905|bibcode=1964Sci...143.1190H|s2cid=27169110}}</ref> The simple act of recollection can dilate the size of the pupil,<ref>{{Cite book|title=Psychophysiology: Human Behavior and Physiological Response (Psychophysiology: Human Behavior & Physiological Response) |edition=5th |last=L. Andreassi|first=John|publisher=Psychology Press|year=2006|isbn=978-0805849516}}</ref> however when the brain is required to process at a rate above its maximum capacity, the pupils contract.<ref>{{cite web|url=https://prezi.com/e00bcswh1fhp/my-brain-is-overloaded/|title=My Brain is Overloaded|website=prezi.com |access-date=2017-02-28}}</ref> There is also evidence that pupil size is related to the extent of positive or negative emotional arousal experienced by a person.<ref name="Partala and Surakka (2003)">{{cite journal|author1=Partala, T.  |author2=Surakka, V. |name-list-style=amp |title=Pupil size variation as an indication of affective processing|journal=International Journal of Human-Computer Studies|volume=59|issue=1–2|pages=185–198|doi=10.1016/S1071-5819(03)00017-X|year=2003|s2cid=7007209 }}</ref>

[[Near-sightedness|Myopic]] individuals have [[Mydriasis|larger]] resting and dark dilated pupils than [[Far-sightedness|hyperopic]] and [[Emmetropia|emmetropic]] individuals, likely due to requiring less accommodation (which results in pupil constriction).<ref>{{Cite journal |last1=Cakmak |first1=Hasan Basri |last2=Cagil |first2=Nurullah |last3=Simavlı |first3=Hüseyin |last4=Duzen |first4=Betul |last5=Simsek |first5=Saban |date=February 2010 |title=Refractive Error May Influence Mesopic Pupil Size |url=http://www.tandfonline.com/doi/full/10.3109/02713680903447892 |journal=Current Eye Research |language=en |volume=35 |issue=2 |pages=130–136 |doi=10.3109/02713680903447892 |pmid=20136423 |s2cid=27407880 |issn=0271-3683}}</ref>

Some humans are able to exert direct control over their [[Iris (anatomy)|iris]] muscles, giving them the ability to manipulate the size of their pupils (i.e. dilating and constricting them) on command, without any changes in lighting condition or eye [[Accommodation (vertebrate eye)|accommodation]] state.<ref>{{Cite journal |last1=Eberhardt |first1=Lisa V. |last2=Grön |first2=Georg |last3=Ulrich |first3=Martin |last4=Huckauf |first4=Anke |last5=Strauch |first5=Christoph |date=2021-10-01 |title=Direct voluntary control of pupil constriction and dilation: Exploratory evidence from pupillometry, optometry, skin conductance, perception, and functional MRI |url=https://www.sciencedirect.com/science/article/pii/S0167876021008448 |journal=International Journal of Psychophysiology |volume=168 |pages=33–42 |doi=10.1016/j.ijpsycho.2021.08.001 |pmid=34391820 |issn=0167-8760}}</ref> However, this ability is likely very rare and its purpose or advantages over those without it are unclear.