Editing Epicanthic fold

{{Short description|Skin fold of the upper eyelid}}
{{Use British English|date=November 2022}}
{{Use dmy dates|date=November 2022}}
{{Infobox anatomy
| Name        = Epicanthic fold
| pronunciation = {{IPAc-en|,|ɛ|p|ɪ|ˌ|k|æ|n|θ|ɪ|k|_|ˈ|f|oʊ|l|d}}<ref>{{cite book|last=Wells|first=John|author-link=John C. Wells|title=Longman Pronunciation Dictionary|publisher=Pearson Longman|edition=3rd|date=3 April 2008|isbn=978-1-4058-8118-0}}</ref>
| synonyms    = Epicanthal fold, epicanthus, eye fold,<ref>{{cite web |title=Eye fold |url=http://www.thefreedictionary.com/eyefold}}</ref> [[Mongoloid]] fold,<ref name="Anthropology">{{cite book |first=Ram Narayan |last=Das |title=Sterling Dictionary of Anthropology |publisher=Sterling |year=1997 |url=https://books.google.com/books?id=AkH911DbJf4C |isbn=9788173590689 }}</ref> palpebronasal fold<ref>{{cite dictionary |url=http://www.medilexicon.com/medicaldictionary.php?s=palpebronasal+fold |title= Palpebronasal Fold - Medical Dictionary Search | dictionary=[[Stedman's Medical Dictionary]] |year= 2006 |access-date=1 October 2009}}</ref>
| Image       = Epicanthic KR02.jpg
| Caption     = A [[Koreans|Korean]] girl with the skin fold of the upper eyelid covering the inner angle of the eye
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| Latin       = plica palpebronasalis<ref>{{cite news|url=http://health.allrefer.com/health/epicanthal-folds-info.html |title=AllRefer Health – Epicanthal Folds (Plica Palpebronasalis) |publisher=AllRefer.com |access-date=1 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100112093315/http://health.allrefer.com/health/epicanthal-folds-info.html |archive-date=12 January 2010 }}</ref>
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| Precursor   =
| System      =
| Artery      =
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An '''epicanthic fold''' or '''epicanthus'''<ref>{{cite web|url=https://medical-dictionary.thefreedictionary.com/epicanthus|title=Epicanthus {{!}} definition of epicanthus by Medical dictionary|access-date=21 July 2020}}</ref> is a [[skin fold]] of the upper [[eyelid]] that covers the inner corner (medial [[canthus]]) of the [[Human eye|eye]].<ref name="Anthropology"/> However, variation occurs in the nature of this feature and the presence of "partial epicanthic folds" or "slight epicanthic folds" is noted in the relevant literature.<ref>Powell, M. L. (1981) ''Assessment and management of developmental changes and problems in children'', Mosby, Incorporated, p. 38 {{ISBN|9780801615207}}</ref><ref>U. Schilbach, U. and Rott, H-D. (1988) ''Ocular Hypotelorism, Submucosal Cleft Palate, and Hypospadias: A New Autosomal Dominant Syndrome'', American Journal of Medical Genetics 31, pp. 863–870</ref><ref name="Berel2000">{{cite book|editor-last=Lang |editor-first=Berel |year=2000 |title=Race and Racism in Theory and Practice |url=https://books.google.com/books?id=VOtU0FzgFPUC&pg=PA10|publisher=Rowman & Littlefield|page=10 |isbn=9780847696932}}</ref> Various factors influence whether epicanthic folds form, including ancestry, age, and certain medical conditions.

The primary cause of the epicanthic fold is the [[hypertrophy]] of the preseptal portion of the orbicularis oculi muscle.<ref>{{Cite journal |title= A comparative retrospective analysis: Myocutaneous flap versus skin flap in V-Y medial epicanthal fold reconstruction|date=2024 |doi=10.3389/fsurg.2024.1335796 |doi-access=free |last1=Wang |first1=Bulin |last2=Zhang |first2=Shengchang |last3=Chen |first3=Yi |last4=Liu |first4=Zhihong |last5=Yu |first5=Jiangang |last6=Zhou |first6=Huimin |last7=Pan |first7=Er |journal=Frontiers in Surgery |volume=11 |pmid=38486795 |pmc=10937365 }}</ref><ref>{{Cite journal |title= Reconsideration of the Epicanthus: Evolution of the Eyelid and the Devolutional Concept of Asian Blepharoplasty|date=2015 |pmc=4536067 |last1=Kwon |first1=B. |last2=Nguyen |first2=A. H. |journal=Seminars in Plastic Surgery |volume=29 |issue=3 |pages=171–183 |doi=10.1055/s-0035-1556849 |pmid=26306084 }}</ref><ref>{{Cite book |title= Textbook of Aging Skin|chapter=Update on Asian Eyelid Anatomy and Periocular Aging Change |date=2015 |doi=10.1007/978-3-642-27814-3_157-1 |chapter-url=https://link.springer.com/referenceworkentry/10.1007/978-3-642-27814-3_157-1 |last1=Saonanon |first1=Preamjit |last2=Whipple |first2=Katherine M. |pages=1–13 |isbn=978-3-642-27814-3 }}</ref>

== Etymology ==
''Epicanthus'' means 'above the [[canthus]]', with epi-canthus being the Latinized form of the Ancient Greek {{wikt-lang|grc|ἐπί}} {{wikt-lang|grc|κανθός}}: 'corner of the eye'.

== Classification ==
[[File:Epicanthic Fold.jpg|thumb|300x300px|This image highlights the epicanthic folds in a person of [[Mongol]] descent.]]
Variation in the shape of the epicanthic fold has led to four types being recognised:

* '''''Epicanthus supraciliaris''''' runs from the brow, curving downwards towards the [[lachrymal sac]].
* '''''Epicanthus palpebralis''''' begins above the upper [[Tarsus (eyelids)|tarsus]] and extends to the inferior orbital rim.
* '''''Epicanthus tarsalis''''' originates at the upper eyelid crease and merges into the skin near the medial canthus. This is the type most often found in East Asians.
* '''''Epicanthus inversus''''' runs from the lower eyelid skin over the medial canthus and extends to the upper lid.<ref>Nguyen, M.Q., Hsu, P.W. and Dinh, T.A. (2009) ''Asian Blepharoplasty'', Semin Plast Surg. 2009 Aug; 23(3), pp. 185–197 doi: 10.1055/s-0029-1224798, p. 189</ref>

== Ethnogeographic distribution ==

=== High-frequency populations ===
The highest frequency of occurrence of epicanthic folds is found in specific populations or ethnicities: [[East Asians]], [[Southeast Asians]], [[Central Asians]], [[North Asians]], [[Polynesians]], [[Micronesians]], [[Indigenous peoples of the Americas]], [[Sámi people]] and some [[African people]] (especially among [[Khoisan]] and [[Nilotic people]]). Among [[South Asians]], they occur at very high frequencies among the [[Nepalis]], [[Bhutan]]ese,<ref name="LivingRacesofMan">{{cite web |url=https://books.google.com/books?id=qepKAAAAYAAJ |title=The Living Races of Man |first1=Carleton Stevens |last1=Coon |first2=Edward E. |last2=Hunt |author1-link=Carleton S. Coon |author2-link=Edward Eyre Hunt Jr. |date=21 April 1966 |publisher=Cape |via=Google Books}}</ref>{{better source needed|date=August 2021|reason=Coon's work contains a lot of valuable data, but as a whole it is considered pseudo-scientific today}} [[Northeast India]]ns,<ref name="LivingRacesofMan" /> [[Kirati people]] and certain [[Adivasi]]<ref name="LivingRacesofMan" /> tribes of [[East India|Eastern]] and [[South India|Southern India]]. It is also commonly found in [[North India|Northern India]], especially in [[Kashmir]]. The [[Hazaras|Hazara people]] in Afghanistan and Pakistan commonly have this trait. Some people in Eastern/Northern Pakistan have this trait. 

In some of these populations, the trait is almost universal. This is especially true in East Asians and Southeast Asians, where a majority, up to 90% in some estimations, of adults have this feature.<ref>{{cite journal |last1=Lee |first1=Yoonho |last2=Lee |first2=Euitae |last3=Park |first3=Won Jin |title=Anchor Epicanthoplasty Combined with OutFold Type Double Eyelidplasty for Asians: Do We Have to Make an Additional Scar to Correct the Asian Epicanthal Fold? |journal=Plastic and Reconstructive Surgery |date=2000 |volume=105|issue=5 |pages=1866-70; discussion 1871 |doi=10.1097/00006534-200004050-00040 |pmid=10809118 |url=https://journals.lww.com/plasreconsurg/Abstract/2000/04050/Anchor_Epicanthoplasty_Combined_with_OutFold_Type.40.aspx}} {{closed access}}</ref>

=== Lower-frequency populations ===
Epicanthic folds also occur, at a considerably lower frequency, in other populations: [[Europeans]] (e.g., [[Scandinavians]], [[English people|English]], [[Irish people|Irish]],<ref>{{Cite news|url=https://www.nytimes.com/1985/10/08/science/q-a-061233.html|title=Q&A|date=8 October 1985|newspaper=The New York Times|issn=0362-4331|access-date=12 November 2016}}</ref> [[Hungarians]], [[Russians]], [[Polish people|Poles]], [[Lithuanians]], [[Latvians]], [[Finns]], and [[Estonians]]),<ref>{{cite encyclopedia|title=epicanthic fold (anatomy)|url=https://www.britannica.com/EBchecked/topic/189688/epicanthic-fold|encyclopedia=Encyclopædia Britannica|access-date=25 April 2014}}</ref><ref>{{cite book |last=Montagu |first=A. |year=1989 |title=Growing Young |publisher=Bergin & Garvey |location=Granby, Mass |edition=2nd |isbn=978-0-89789-166-0 }}</ref> [[Jews]], South Asians ([[Bengalis]],<ref name="LivingRacesofMan" /> [[Sinhalese people|Sinhalese]],<ref>{{cite journal |doi=10.1525/aa.1963.65.3.02a00260 |volume=65 |issue=3 |title=The Physical Anthropology of Ceylon. Howard W. Stoudt. |journal=American Anthropologist |pages=694–695 |year=1963 |last1=Angel |first1=J. Lawrence|doi-access=free }}</ref> among other groups in eastern and southern South Asia),<ref name="LivingRacesofMan" /> [[Nilotes]], [[Cushitic peoples|Cushites]], and [[Amazigh]] people.<ref>{{cite journal|title=Mongolism in Sudanese children|journal=Journal of Tropical Pediatrics|date=September 1962|volume=8|issue=2|pages=48–50|pmid=13905256|doi=10.1093/oxfordjournals.tropej.a057626|last1=Hassan|first1=M. M.}}</ref>

=== Perception and attribution ===
[[File:Jens Byggmark Schladming 2008.jpg|thumb|Swedish ski racer [[Jens Byggmark]] with an epicanthic fold over his left eye|alt=]]
The degree of development of the fold between individuals varies greatly, and attribution of its presence or absence is often subjective, being to a degree relative to the occurrence of the trait within the community of the specific observer. Also, its frequency varies but can be found in peoples all over the world. Its use, therefore, as a [[phenotypic]] marker to define biological populations is debatable.<ref name="Berel2000" />

== Possible evolutionary function ==
The epicanthic fold is often associated with greater levels of fat deposition around the eyeball. The adipose tissue is thought to provide greater insulation for the eye and sinuses from the effects of cold, especially from freezing winds, and to represent an adaptation to cold climates. It has also been postulated that the fold itself may provide a level of protection from [[snow blindness]]. Though its appearance in peoples of Southeast Asia can be linked to possible descent from cold-adapted ancestors, this does not explain its occurrence in various African peoples. The epicanthic fold found in many African people has been tentatively linked to protection for the eye from the high levels of [[ultraviolet]] light found in desert and semi-desert areas.<ref>{{cite book|editor-last=Lang |editor-first=Berel |year=2000 |title=Race and Racism in Theory and Practice |url=https://books.google.com/books?id=VOtU0FzgFPUC&pg=PA10|publisher=Rowman & Littlefield|pages=10–11 |isbn=9780847696932}}</ref>

The exact evolutionary function and origin of epicanthic folds remains unknown. Scientific explanations include either random variation and selection (presumably [[sexual selection]]), or possible adaption to desert environment and/or high levels of ultraviolet light found in high-altitude environments, such as the [[Himalayas]].

Dr. Frank Poirier, a physical anthropologist at [[Ohio State University]], said that the epicanthic fold among Asian people is often explained as part of an adaptation to severe cold or tropical environments, however he suggests that neither of these explanations are sufficient to explain its presence in East and Southeast Asia, and notes that the fold can also  be observed in [[Irish people|Irish]] and African people. He attributes the epicanthic fold to [[pleiotropic]] genes that control more than one characteristic or function. He also did not offer an explanation for the origin of epicanthic folds.<ref>{{cite news |title=ORIGIN OF SHAPE OF ASIAN EYES IS STILL A MYSTERY TO SCIENTISTS |url=https://www.chicagotribune.com/news/ct-xpm-1985-10-13-8503100141-story.html |work=Chicago Tribune}} "Dr. Frank Poirier, a physical anthropologist at Ohio State University, says the classical explanation of epicanthic fold depicts it as an adaptation to the tropical and arctic regions where many Asians live. The fold is described as a sun visor protecting the eyes from overexposure to ultraviolet radiation or as a blanket insulating them from the cold. According to Poirier, the problem with this theory is that a substantial portion of the Asian population evolved in areas outside of the tropical and arctic regions. In addition, he says epicanthic fold is not limited to Asians. ''John F. Kennedy had a variance of the fold and it is found among Europeans, especially the Irish,'' he said. ''It's just less prevalent.'' The fold is also found among infants worldwide. Poirier attributes the fold to pleiotropic genes--single genes that control more than one characteristic or function--but he has no explanation for its origin."</ref>

== Other factors ==
[[File:Bosquimanos-Grassland Bushmen Lodge, Botswana 03.jpg|thumb|The [[Khoi]], the [[San people|San]] and some other African groups have a high frequency of the epicanthic fold.]]

=== Age ===
Many [[fetus]]es lose their epicanthic folds after three to six months of gestation.<ref>{{Cite journal |last=Park JI |date=1 January 2000 |title=Modified Z-Epicanthoplasty in the Asian Eyelid |url=http://archfaci.jamanetwork.com/article.aspx?articleid=479760 |journal=Archives of Facial Plastic Surgery |volume=2 |issue=1 |pages=43–47 |issn=1521-2491 |doi=10.1001/archfaci.2.1.43 |pmid=10925423}}</ref> Epicanthic folds may be visible in the development stages of young children of any ethnicity, especially before the nose bridge fully develops.<ref>{{cite web |title=Epicanthal folds |url=https://medlineplus.gov/ency/article/003030.htm |website=MedlinePlus |publisher=U.S National Library of Medicine}}</ref>

=== Medical conditions ===
Epicanthic fold prevalence can sometimes be found as a sign of congenital abnormality, such as in [[Zellweger syndrome]]<ref>{{cite journal |last1=Kalyanasundaram |first1=S. |first2=Samuel E. |last2=Ibhanesebhor |first3=Chikkanayakanahalli M. |last3=Manjunatha |year=2010 |display-authors=1 |title=Peroxisomal Disorder-Unusual Presentation as Failure to Thrive in Early Infancy |journal=Indian Journal of Pediatrics |volume=77 |issue=10 |pages=1151–1152 |doi=10.1007/s12098-010-0199-6 |pmid=20872098 |s2cid=5736554 }}</ref> and [[Noonan syndrome]]. Medical conditions that cause the nasal bridge not to develop and project are also associated with epicanthic fold. About 60% of individuals with [[Down syndrome]] (also known as trisomy 21) have prominent epicanthic folds.<ref name=Steph2010>{{cite book |last1=Hammer |first1=Gary, D. |last2=McPhee |first2=Stephen J. |title=Pathophysiology of Disease: An Introduction to Clinical Medicine |year=2010 |publisher=McGraw-Hill Medical |location=New York |isbn=978-0-07-162167-0 |edition=6 |chapter=Pathophysiology of Selected Genetic Diseases}}</ref><ref>Pham, V. (2010). COMMON OTOLARYNGOLOGICAL CONGENITAL ABNORMALITIES. UTMB, Dept. of Otolaryngology. [http://www.utmb.edu/otoref/grnds/congenital-abnormal-101122/congen-abnom-101122.pdf] {{Webarchive|url=https://web.archive.org/web/20111006044747/http://www.utmb.edu/otoref/Grnds/congenital-abnormal-101122/congen-abnom-101122.pdf|date=6 October 2011}}</ref>

Other examples are [[fetal alcohol syndrome]], [[phenylketonuria]], and [[Turner syndrome]].<ref>{{cite web|url=https://medlineplus.gov/ency/article/003030.htm |title=Epicanthal folds |first1=Neil K. |last1=Kaneshiro |first2=David |last2=Zieve |first3=Isla |last3=Ogilvie |work=[[MedlinePlus]]}}</ref>[[File:Epicanthic KR07.jpg|thumb|Epicanthic folds ('''Note that the tarsal plates are exposed Laterally.''')]]
== Misclassification of monolids and epicanthic folds ==
Monolids and epicanthic folds are often used interchangeably, but they refer to different eyelid types. Monolids are characterized by the absence of an upper eyelid crease, with the [[Tarsus (eyelids)|tarsal plates]] being obscured. In contrast, epicanthic folds are defined by the presence of excess upper eyelid skin that forms a curve over the inner corners of the eyes, while the [[Tarsus (eyelids)|tarsal plates]] remain exposed completely or laterally.[[File:Epicanthicfold.JPG|thumb|Monolids ('''In Monolids, the tarsal plate is barely visible or not noticeable at all.''')]]

== See also ==
* [[Blepharitis]]
* [[Epicanthoplasty]], the surgical modification of epicanthic folds
* [[Human physical appearance]]

== References ==
{{Reflist}}

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

{{Accessory organs of the eye|state=collapsed}}

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[[Category:Human eye anatomy]]
[[Category:Facial features]]
[[Category:Skin anatomy]]
[[Category:Eye]]