View source for Blinking

{{short description|Rapid closing and opening of the eyelid}}
{{Use dmy|date=May 2023}}
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[[File:Eye opening and closing.gif|thumb|{{center|{{PAGENAME}}}}]]

'''Blinking''' is a bodily function; it is a [[autonomic nervous system|semi-autonomic]] rapid closing of the [[eyelid]].<ref name="d.umn.edu">{{cite web|url=http://www.d.umn.edu/~jfitzake/Lectures/DMED/Vision/Optics/Blinking.html|title=Blinking}}</ref> A single blink is determined by the forceful closing of the eyelid or inactivation of the [[levator palpebrae superioris]] and the activation of the palpebral portion of the [[orbicularis oculi]], not the full open and close.{{citation needed|date=February 2016}} It is an essential function of the [[eye]] that helps spread [[tears]] across and remove irritants from the surface of the [[cornea]] and [[conjunctiva]].

Blinking may have other functions since it occurs more often than necessary just to keep the eye lubricated. Researchers think{{weasel inline|date=January 2025}} blinking may help with disengagement of attention; following blink onset, cortical activity decreases in the dorsal network and increases in the default-mode network, associated with internal processing.<ref>{{cite journal |doi=10.1073/pnas.1214804110 |pmid=23267078 |pmc=3545766 |jstor=42553853 |title=Blink-related momentary activation of the default mode network while viewing videos |journal=[[Proceedings of the National Academy of Sciences]] |volume=110 |issue=2 |pages=702–6 |year=2012 |last1=Nakano |first1=T. |last2=Kato |first2=M. |last3=Morito |first3=Y. |last4=Itoi |first4=S. |last5=Kitazawa |first5=S. |bibcode=2013PNAS..110..702N |doi-access=free }}</ref> Blink speed can be affected by elements such as fatigue, eye injury, medication, and disease. The blinking rate is determined by the "blinking center", but it can also be affected by external stimulus.

Some animals, such as [[tortoise]]s and [[hamster]]s, blink their eyes independently of each other. Humans use [[wink]]ing, the blinking of only one eye, as a form of [[body language]].

==Function and anatomy==
[[File:Bird blink-edit.jpg|thumb|right|Birds, reptiles and sharks blink with a [[nictitating membrane]] from one side of the eye to the other.]]
Blinking provides moisture to the eye by irrigation using tears and a lubricant the eyes secrete. The eyelid provides suction across the eye from the tear duct to the entire eyeball to keep it from drying out.
[[File:Closed human eye, superior view.jpg|thumb|Closed eye of a human, displaying [[eyelashes]] which function to catch irritants when the eye is blinked.]]
Blinking also protects the eye from irritants. [[Eyelash]]es are hairs which grow from the edges of the upper and lower [[Eyelid|eyelids]] that create a line of defense against dust and other elements to the eye. The eyelashes catch most of these irritants before they reach the eyeball.

There are multiple muscles that control reflexes of blinking. The main muscles, in the upper eyelid, that control the opening and closing are the [[orbicularis oculi]] and [[levator palpebrae superioris muscle]]. The orbicularis oculi closes the eye, while the contraction of the levator palpebrae muscle opens the eye. The Müller's muscle, or the [[superior tarsal muscle]], in the upper eyelid and the inferior palpebral muscle in the lower 3 eyelid are responsible for widening the eyes. These muscles are not only imperative in blinking, but they are also important in many other functions such as squinting and winking.  The inferior palpebral muscle is coordinated with the inferior rectus to pull down the lower lid when one looks down.

The correlation between human eyelid blink behavior and [[psychological stress]] was also demonstrated by means of a laboratory study.<ref>N Reßut (2021): ''Das Lidschlagverhalten als Indikator psychischer Belastung'', Wiesbaden: Springer Vieweg, 2021. DOI: https://doi.org/10.1007/978-3-658-36052-8 – ISBN 978-3-658-36051-1</ref><ref>N Reßut & A Hoppe (2019): ''Erfassung von individuellem Beanspruchungserleben bei kognitiven Belastungssituationen mittels Mustererkennung im Lidschlagverhalten.'' In: Zeitschrift für Arbeitswissenschaft 65 (2019), S. 1–13. DOI: https://doi.org/10.1007/s41449-019-00165-y. – ISSN 0340-2444</ref> Lying may affect the rate of blinking.<ref>{{Cite journal|url=https://link.springer.com/article/10.1007/s10919-008-0051-0|doi = 10.1007/s10919-008-0051-0|title = Blinking During and After Lying|year = 2008|last1 = Leal|first1 = Sharon|last2 = Vrij|first2 = Aldert|journal = Journal of Nonverbal Behavior|volume = 32|issue = 4|pages = 187–194|s2cid = 43996756|url-access = subscription}}</ref> 

Blinking is used for communication in humans,<ref name="p574">{{cite journal |last1=Hömke |first1=Paul |last2=Holler |first2=Judith |last3=Levinson |first3=Stephen C. |date=2018 |title=Eye blinks are perceived as communicative signals in human face-to-face interaction |journal=PLOS ONE |volume=13 |issue=12 |page=e0208030 |doi=10.1371/journal.pone.0208030 |issn=1932-6203 |doi-access=free|pmid=30540819 |pmc=6291193 |bibcode=2018PLoSO..1308030H |hdl=21.11116/0000-0002-7F3D-D |hdl-access=free }}</ref> some primates,<ref name="o381">{{cite journal |last1=Tada |first1=Hideoki |last2=Omori |first2=Yasuko |last3=Hirokawa |first3=Kumi |last4=Ohira |first4=Hideki |last5=Tomonaga |first5=Masaki |date=2013 |title=Eye-Blink Behaviors in 71 Species of Primates |journal=PLOS ONE |volume=8 |issue=5 |page=e66018 |doi=10.1371/journal.pone.0066018 |issn=1932-6203 |doi-access=free|pmid=23741522 |bibcode=2013PLoSO...866018T }}</ref> in human interactions with cats,<ref name="e356">{{cite journal |last1=Humphrey |first1=Tasmin |last2=Proops |first2=Leanne |last3=Forman |first3=Jemma |last4=Spooner |first4=Rebecca |last5=McComb |first5=Karen |date=2020-10-05 |title=The role of cat eye narrowing movements in cat–human communication |journal=Scientific Reports |volume=10 |issue=1 |page= 16503|doi=10.1038/s41598-020-73426-0 |issn=2045-2322 |doi-access=free|pmid=33020542 |pmc=7536207 |bibcode=2020NatSR..1016503H }}</ref>  and by female concave-eared torrent frogs to initiate mating with males.<ref name="s453">{{cite journal |last1=Chen |first1=Pan |last2=Liu |first2=Shuwen |last3=Wu |first3=Yatao |last4=Liu |first4=Guoqing |last5=Jin |first5=Yingying |last6=Zhang |first6=Fang |year=2024 |title=Female frogs communicate with males through blinking |journal=Current Biology |volume=34 |issue=5 |pages=R191–R192 |doi=10.1016/j.cub.2024.01.023 |pmid=38471444 |bibcode=2024CBio...34.R191C |issn=0960-9822}}</ref> 

===Central nervous system's control===
Though one may think that the stimulus triggering blinking is dry or irritated eyes, it is most likely that it is controlled by a "blinking center" of the [[globus pallidus]] of the [[lenticular nucleus]]—a body of nerve cells between the base and outer surface of the brain.  Nevertheless, external stimuli can contribute. The orbicularis oculi is a facial muscle; therefore its actions are translated by the [[facial nerve]] root. The levator palpebrae superioris' action is sent through the [[oculomotor nerve]]. The duration of a blink is
on average 100–150 milliseconds according to UCL researcher<ref>{{cite web|url=https://www.ucl.ac.uk/news/2005/jul/blink-and-you-miss-it|title=Blink and you miss it|date=2005-08-03}}</ref> and between 100 and 400 ms according to the Harvard Database of Useful Biological Numbers.<ref>{{cite web|url=http://bionumbers.hms.harvard.edu/bionumber.aspx?s=y&id=100706&ver=0|title=Average duration of a single eye blink – Human Homo sapiens – BNID 100706}}</ref> Closures in excess of 1000 ms were defined as [[microsleep]]s.

Greater activation of  dopaminergic pathways dopamine production in the [[striatum]] is associated with a higher rate of spontaneous eye blinking.<ref>{{cite journal | last1 = Taylor | first1 = JR | last2 = Elsworth | first2 = JD | last3 = Lawrence | first3 = MS | last4 = Sladek Jr | first4 = JR | last5 = Roth | first5 = RH | last6 = Redmond Jr | first6 = DE | title = Spontaneous blink rates correlate with dopamine levels in the caudate nucleus of MPTP-treated monkeys | journal = Experimental Neurology | volume = 158 | issue = 1 | pages = 214–20 | year = 1999 | pmid = 10448434 | doi = 10.1006/exnr.1999.7093 | s2cid = 43504305 | doi-access = free }}</ref><ref>{{cite journal | last1 = Colzato | first1 = LS | last2 = Van Den Wildenberg | first2 = WP | last3 = Van Wouwe | first3 = NC | last4 = Pannebakker | first4 = MM | last5 = Hommel | first5 = B | title = Dopamine and inhibitory action control: evidence from spontaneous eye blink rates | journal = Experimental Brain Research. Experimentelle Hirnforschung. Experimentation Cerebrale | volume = 196 | issue = 3 | pages = 467–74 | year = 2009 | pmid = 19484465 | pmc = 2700244 | doi = 10.1007/s00221-009-1862-x }}</ref> Conditions in which there is reduced dopamine availability such as [[Parkinson's disease]] have reduced eye blink rate,<ref>{{cite journal | last1 = Deuschl | first1 = G | last2 = Goddemeier | first2 = C | title = Spontaneous and reflex activity of facial muscles in dystonia, Parkinson's disease, and in normal subjects | journal = [[Journal of Neurology, Neurosurgery, and Psychiatry]] | volume = 64 | issue = 3 | pages = 320–4 | year = 1998 | pmid = 9527141 | pmc = 2169979 | doi=10.1136/jnnp.64.3.320}}</ref> while conditions in which it is raised such as [[schizophrenia]] have an increased rate.<ref>{{cite journal | last1 = Freed | first1 = WJ | last2 = Kleinman | first2 = JE | last3 = Karson | first3 = CN | last4 = Potkin | first4 = SG | last5 = Murphy | first5 = DL | last6 = Wyatt | first6 = RJ | title = Eye-blink rates and platelet monoamine oxidase activity in chronic schizophrenic patients | journal =[[Biological Psychiatry (journal)|Biological Psychiatry]] | volume = 15 | issue = 2 | pages = 329–32 | year = 1980 | pmid = 7417620 }}</ref> Blink rate is associated with dopamine-related executive function and creativity.<ref>{{Cite journal|last1=Jongkees|first1=Bryant J.|last2=Colzato|first2=Lorenza S.|date=December 2016|title=Spontaneous eye blink rate as predictor of dopamine-related cognitive function—A review|url=https://linkinghub.elsevier.com/retrieve/pii/S0149763416302846|journal=Neuroscience & Biobehavioral Reviews|language=en|volume=71|pages=58–82|doi=10.1016/j.neubiorev.2016.08.020|pmid=27555290|s2cid=25094074|url-access=subscription}}</ref><ref>{{Cite journal|last1=Chermahini|first1=Soghra Akbari|last2=Hommel|first2=Bernhard|date=2010-06-01|title=The (b)link between creativity and dopamine: Spontaneous eye blink rates predict and dissociate divergent and convergent thinking|url=https://www.sciencedirect.com/science/article/pii/S0010027710000715|journal=Cognition|language=en|volume=115|issue=3|pages=458–465|doi=10.1016/j.cognition.2010.03.007|pmid=20334856|s2cid=14791691|issn=0010-0277|url-access=subscription}}</ref><ref>{{Cite journal|last1=Kuwamizu|first1=Ryuta|last2=Suwabe|first2=Kazuya|last3=Damrongthai|first3=Chorphaka|last4=Fukuie|first4=Takemune|last5=Ochi|first5=Genta|last6=Hyodo|first6=Kazuki|last7=Hiraga|first7=Taichi|last8=Nagano-Saito|first8=Atsuko|last9=Soya|first9=Hideaki|date=July 2021|title=Spontaneous Eye Blink Rate Connects Missing Link between Aerobic Fitness and Cognition|url=https://journals.lww.com/10.1249/MSS.0000000000002590|journal=Medicine & Science in Sports & Exercise|language=en|volume=53|issue=7|pages=1425–1433|doi=10.1249/MSS.0000000000002590|pmid=33433152|s2cid=231585782|issn=1530-0315|url-access=subscription}}</ref>

===Evolutionary origins===
Blinking is present in all major [[tetrapod]] [[crown group]]s. The soft tissues involved in blinking have not been preserved in the fossil record, but study of [[mudskipper]]s (a group of amphibious fish species that evolved blinking [[Convergent evolution|independently]] from other tetrapod species, but for similar purposes), suggest that blinking (which involves the eye retracting in mudskippers) may have arose in response to [[Natural selection|selective pressures]] upon species shifting from aquatic to terrestrial habitats. For example, compared to an aquatic environment, in a terrestrial environment, the corneal cells must be kept moist such that vital substances like oxygen can more easily diffuse into them, detritus may adhere to the eye in dry conditions, and objects may move towards the eye at faster and more dangerous speeds in air than in water. Additionally, when at their fully aquatic juvenile stage of development, their eyes are not in the positioning with which they blink, but as adults, their eyes elevate to a position that can blink, which they do when they are not submerged or bump into a surface, suggesting blinking emerged as an adaptation to terrestrial life as opposed to aquatic life.<ref name="mudskipper">{{cite journal |last1=Aiello |first1=Brett R. |last2=Bhamla |first2=M. Saad |last3=Gau |first3=Jeff |last4=Morris |first4=John G. L. |last5=Bomar |first5=Kenji |last6=da Cunha |first6=Shashwati |last7=Fu |first7=Harrison |last8=Laws |first8=Julia |last9=Minoguchi |first9=Hajime |last10=Sripathi |first10=Manognya |last11=Washington |first11=Kendra |last12=Wong |first12=Gabriella |last13=Shubin |first13=Neil H. |last14=Sponberg |first14=Simon |last15=Stewart |first15=Thomas A. |date=April 24, 2023 |title=The origin of blinking in both mudskippers and tetrapods is linked to life on land |journal=[[PNAS]] |volume=120 |issue=18 |pages=e2220404120 |doi=10.1073/pnas.2220404120 |pmid=37094121 |pmc=10160996 |doi-access=free|bibcode=2023PNAS..12020404A }}</ref>

Early tetrapods in the transition to land, which would later yield all non-mudskipper blinking species, possessed similar characteristics regarding eye positioning that suggest blinking arose in response to aerial vision and terrestrial lifestyle.<ref name="mudskipper" />

==Types of blinking==
There are three types of blinking.

===Spontaneous blink===
Spontaneous blinking is done without external stimuli and internal effort. This type of blinking is conducted in the pre-motor brain stem and happens without conscious effort, like [[breathing]] and [[digestion]].

===Reflex blink===
A [[Corneal reflex|reflex blink]] occurs in response to an external stimulus, such as contact with the [[cornea]] or objects that appear rapidly in front of the eye. A reflex blink is not necessarily a conscious blink either; however it does happen faster than a spontaneous blink.<ref name="d.umn.edu"/> Reflex blink may occur in response to [[Touch|tactile]] [[Stimulus (physiology)|stimuli]] (e.g., [[corneal]], [[eyelash]], skin of [[eyelid]], contact with [[eyebrow]]), [[optical]] stimuli (e.g. [[dazzle reflex]],<ref>{{cite journal |doi=10.1111/j.1475-1313.2006.00350.x |pmid=16684158 |title=The dazzle reflex: Electrophysiological signals from ocular muscles reveal strong binocular summation effects |journal=Ophthalmic and Physiological Optics |volume=26 |issue=3 |pages=318–25 |year=2006 |last1=Plainis |first1=S. |last2=Murray |first2=I. J. |last3=Carden |first3=D. |s2cid=27075991 }}</ref> or [[menace reflex]]) or [[Hearing|auditory]] stimuli (e.g., [[menace reflex]]).

===Voluntary blink===
A voluntary blink is a conscious blink, with the use of all 3 divisions of the [[orbicularis oculi]] muscle.

==Blinking in everyday life==

===Children===
Infants do not blink at the same rate of adults; in fact, infants only blink at an average rate of one or two times in a minute.<ref>Zametkin, Alan J., Janice R. Stevens, and Richard Pittman (1979). "Ontogeny of spontaneous blinking and of habituation of the blink reflex." ''Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society'' 5.5 (1979): 453-457. https://doi.org/10.1002/ana.410050509</ref><ref>Val Danilov I, Mihailova S. (2025). "Reflexes and Shared Intentionality in the Origins of Emotions Development: A Scoping Review of Studies on Blinking in Infants". ''OBM Neurobiology'' 2025; 9(1): 263; https://doi:10.21926/obm.neurobiol.2501263.</ref> The reason for this difference is unknown, but it is suggested that infants do not require the same amount of eye lubrication that adults do because their eyelid opening is smaller in relation to adults. Additionally, infants do not produce [[tears]] during their first month of life. Infants also get a significant amount more sleep than adults do and, as discussed earlier, fatigued eyes blink more. However, throughout childhood the blink rate increases, and by adolescence, it is usually equivalent to that of adults.<ref>{{cite web|url=https://www.theregister.co.uk/2006/06/30/the_odd_body_blinking/|title=Why do babies blink less often than adults?|date=30 June 2006|first=Stephen|last=Juan|website=[[The Register]]}}</ref>

===Adults===
There have been mixed results when studying gender-dependent{{dubious|reason=author may be describing a biological thing, not how societal role affects blinking|date=January 2021}} differences in blinking rates, with results varying from the women's rate nearly doubling the men's to no significant difference between them.<ref>{{cite journal |pmid=12137399 |year=2002 |last1=Doughty |first1=M. J. |title=Further assessment of gender- and blink pattern-related differences in the spontaneous eyeblink activity in primary gaze in young adult humans |journal=[[Optometry and Vision Science]] |publisher=[[American Academy of Optometry]] |volume=79 |issue=7 |pages=439–47 |doi=10.1097/00006324-200207000-00013|s2cid=24140202 }}</ref><ref>{{cite journal |doi=10.1111/j.1475-1313.2008.00577.x |pmid=18565090 |title=Spontaneous blinking in healthy persons: An optoelectronic study of eyelid motion |journal=Ophthalmic and Physiological Optics |volume=28 |issue=4 |pages=345–53 |year=2008 |last1=Sforza |first1=Chiarella |last2=Rango |first2=Mario |last3=Galante |first3=Domenico |last4=Bresolin |first4=Nereo |last5=Ferrario |first5=Virgilio F. |s2cid=542559 }}</ref>  In addition, women using [[oral contraceptives]] blink 32% more often than other women on average for unknown reasons.<ref name="pmid7822673">{{Cite journal
| last1 = Yolton | first1 = D. P.
| last2 = Yolton | first2 = R. L.
| last3 = López | first3 = R.
| last4 = Bogner | first4 = B.
| last5 = Stevens | first5 = R.
| last6 = Rao | first6 = D.
| title = The effects of gender and birth control pill use on spontaneous blink rates
| journal = [[Journal of the American Optometric Association]]
| volume = 65
| issue = 11
| pages = 763–70
| year = 1994
| pmid = 7822673
}}</ref> Generally, between each blink is an interval of 2–10 seconds; actual rates vary by individual, averaging around 17 blinks per minute in a laboratory setting. However, when the eyes are focused on an object for an extended period of time, such as when reading, the rate of blinking decreases to about 4 to 5 times per minute.<ref>{{Cite journal|last1=Bentivoglio|first1=A. R.|last2=Bressman|first2=S. B.|last3=Cassetta|first3=E.|last4=Carretta|first4=D.|last5=Tonali|first5=P.|last6=Albanese|first6=A.|s2cid=12607655|date=November 1997|title=Analysis of blink rate patterns in normal subjects|journal=Movement Disorders|volume=12|issue=6|pages=1028–1034|doi=10.1002/mds.870120629|issn=0885-3185|pmid=9399231}}</ref> This is the major reason that eyes dry out and become fatigued when reading.

When the eyes dry out or become fatigued due to reading on a computer screen, it can be an indication of [[computer vision syndrome]]. Computer vision syndrome can be prevented by taking regular breaks, focusing on objects far from the screen, having a well-lit workplace, or using a blink reminder application. Studies suggest<ref>{{Cite journal|last1=修|first1=福島|last2=正男|first2=斎藤|date=1998-03-31|title=バイオフィードバック法による瞬目の訓練|journal=バイオフィードバック研究|language=ja|volume=25|doi=10.20595/jjbf.25.0_17|issn=0386-1856}}</ref> that adults can learn to maintain a healthy blinking rate while reading or looking at a computer screen using [[biofeedback]].

Eye blinking can be a criterion for diagnosing medical conditions. For example, excessive blinking may help to indicate the onset of [[Tourette syndrome]], [[stroke]]s or disorders of the [[nervous system]]. A reduced rate of blinking is associated with [[Parkinson's disease]].

==See also==
* [[Corneal reflex]]
* [[Reflex]]

==References==
{{reflist|35em}}

== External links ==
* {{commons category-inline}}

[[Category:Eye]]