An epicanthic fold or epicanthus is a
skin fold
Skin folds or skinfolds are areas of skin that are naturally folded. Many skin folds are distinct, heritable anatomical features, and may be used for identification of animal species, while others are non-specific and may be produced either by ind ...
of the upper
eyelid
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyel ...
that covers the inner corner (medial
canthus
The canthus (pl. canthi, palpebral commissures) is either corner of the eye where the upper and lower eyelids meet. More specifically, the inner and outer canthi are, respectively, the medial and lateral ends/angles of the palpebral fissure.
Th ...
) of the
eye.
However, variation occurs in the nature of this feature and the possession of "partial epicanthic folds" or "slight epicanthic folds" is noted in the relevant literature.
[Lang, Berel (ed.) (2000) ''Race and Racism in Theory and Practice'', Rowman & Littlefield, p. 10] Various factors influence whether epicanthic folds form, including ancestry, age, and certain medical conditions.
Etymology
''Epicanthus'' means 'above the
canthus
The canthus (pl. canthi, palpebral commissures) is either corner of the eye where the upper and lower eyelids meet. More specifically, the inner and outer canthi are, respectively, the medial and lateral ends/angles of the palpebral fissure.
Th ...
', with epi-canthus being the Latinized form of the Ancient Greek : 'corner of the eye'.
Classification
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 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.
Ethnogeographic distribution
High-frequency populations
![Uyghur-redhead](https://upload.wikimedia.org/wikipedia/commons/e/e5/Uyghur-redhead.jpg)
The highest frequency of occurrence of epicanthic folds is found in specific populations or ethnicities:
East Asians
East Asian people (East Asians) are the people from East Asia, which consists of China, Taiwan, Japan, Mongolia, North Korea, and South Korea. The total population of all countries within this region is estimated to be 1.677 billion and 21% of t ...
,
Southeast Asians,
Central Asians
Central Asia is a diverse land with many ethnic groups, languages, religions and tribes. The nations which make up Central Asia are five of the former Soviet republics: Kazakhstan, Kyrgyzstan, Turkmenistan, Tajikistan, and Uzbekistan, which have ...
,
North Asians
North Asia or Northern Asia, also referred to as Siberia, is the northern region of Asia, which is defined in geographical terms and is coextensive with the Asian part of Russia, and consists of three Russian regions east of the Ural Mountains: ...
,
Polynesians
Polynesians form an ethnolinguistic group of closely related people who are native to Polynesia (islands in the Polynesian Triangle), an expansive region of Oceania in the Pacific Ocean. They trace their early prehistoric origins to Island Sou ...
,
Micronesians
The Micronesians or Micronesian peoples are various closely related ethnic groups native to Micronesia, a region of Oceania in the Pacific Ocean. They are a part of the Austronesian ethnolinguistic group, which has an Urheimat in Taiwan.
Ethno ...
,
Indigenous peoples of the Americas
The Indigenous peoples of the Americas are the inhabitants of the Americas before the arrival of the European settlers in the 15th century, and the ethnic groups who now identify themselves with those peoples.
Many Indigenous peoples of the A ...
,
Mestizos
(; ; fem. ) is a term used for racial classification to refer to a person of mixed European and Indigenous American ancestry. In certain regions such as Latin America, it may also refer to people who are culturally European even though their ...
, and some
African peoples
African or Africans may refer to:
* Anything from or pertaining to the continent of Africa:
** People who are native to Africa, descendants of natives of Africa, or individuals who trace their ancestry to indigenous inhabitants of Africa
*** Ethn ...
(especially among
Khoisan
Khoisan , or (), according to the contemporary Khoekhoegowab orthography, is a catch-all term for those indigenous peoples of Southern Africa who do not speak one of the Bantu languages, combining the (formerly "Khoikhoi") and the or ( in t ...
and
Nilotic peoples
The Nilotic peoples are people Indigenous peoples of Africa, indigenous to the Nile Valley who speak Nilotic languages. They inhabit South Sudan, Sudan, Ethiopia, Uganda, Kenya, the Democratic Republic of the Congo, Rwanda, Burundi and Tanzania. ...
). Among
South Asians
South Asian ethnic groups are an ethnolinguistic grouping of the diverse populations of South Asia, including the nations of India, Pakistan, Bangladesh, Nepal, Bhutan, the Maldives, and Sri Lanka. While Afghanistan is variously considered to b ...
, they occur at very high frequencies among the
Bhutan
Bhutan (; dz, འབྲུག་ཡུལ་, Druk Yul ), officially the Kingdom of Bhutan,), is a landlocked country in South Asia. It is situated in the Eastern Himalayas, between China in the north and India in the south. A mountainous ...
ese,
Northeast India
, native_name_lang = mni
, settlement_type =
, image_skyline =
, image_alt =
, image_caption =
, motto =
, image_map = Northeast india.png
, ...
ns,
Kirati people
The Kirati people, also spelled as Kirant or Kiranti, are a Sino-Tibetan ethnic group. They are peoples of the Himalayas, mostly the Eastern Himalaya extending eastward from Nepal to North East India (predominantly in the Indian state of Sikkim ...
and certain
Adivasi
The Adivasi refers to inhabitants of Indian subcontinent, generally tribal people. The term is a Sanskrit word coined in the 1930s by political activists to give the tribal people an indigenous identity by claiming an indigenous origin. The term ...
tribes of
eastern India
East India is a region of India consisting of the Indian states of Bihar, Jharkhand, Odisha
and West Bengal and also the union territory of the Andaman and Nicobar Islands. The region roughly corresponds to the historical region of Magadha fr ...
.
In some of these populations the trait is almost universal, specifically in East Asians and Southeast Asians, where a majority, up to 90% in some estimations, of adults have this feature.
Lower-frequency populations
Epicanthic folds also occur, at a considerably lower frequency, in other populations:
Europeans
Europeans are the focus of European ethnology, the field of anthropology related to the various ethnic groups that reside in the states of Europe. Groups may be defined by common genetic ancestry, common language, or both. Pan and Pfeil (2004) ...
(e.g.,
Scandinavians
Scandinavia; Sámi languages: /. ( ) is a subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, Norway, and Swe ...
,
English
English usually refers to:
* English language
* English people
English may also refer to:
Peoples, culture, and language
* ''English'', an adjective for something of, from, or related to England
** English national ide ...
,
Irish
Irish may refer to:
Common meanings
* Someone or something of, from, or related to:
** Ireland, an island situated off the north-western coast of continental Europe
***Éire, Irish language name for the isle
** Northern Ireland, a constituent unit ...
,
Hungarians
Hungarians, also known as Magyars ( ; hu, magyarok ), are a nation and ethnic group native to Hungary () and historical Hungarian lands who share a common culture, history, ancestry, and language. The Hungarian language belongs to the Urali ...
,
Russians
, native_name_lang = ru
, image =
, caption =
, population =
, popplace =
118 million Russians in the Russian Federation (2002 ''Winkler Prins'' estimate)
, region1 =
, pop1 ...
,
Poles
Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a West Slavic nation and ethnic group, who share a common history, culture, the Polish language and are identified with the country of Poland in Ce ...
,
Lithuanians
Lithuanians ( lt, lietuviai) are a Baltic ethnic group. They are native to Lithuania, where they number around 2,378,118 people. Another million or two make up the Lithuanian diaspora, largely found in countries such as the United States, Uni ...
,
Latvians
Latvians ( lv, latvieši) are a Baltic ethnic group and nation native to Latvia and the immediate geographical region, the Baltics. They are occasionally also referred to as Letts, especially in older bibliography. Latvians share a common Latvi ...
,
Finns
Finns or Finnish people ( fi, suomalaiset, ) are a Baltic Finnic ethnic group native to Finland.
Finns are traditionally divided into smaller regional groups that span several countries adjacent to Finland, both those who are native to these ...
,
Estonians
Estonians or Estonian people ( et, eestlased) are a Finnic ethnic group native to Estonia who speak the Estonian language.
The Estonian language is spoken as the first language by the vast majority of Estonians; it is closely related to other ...
and
Samis), South Asians (
Bengalis
Bengalis (singular Bengali bn, বাঙ্গালী/বাঙালি ), also rendered as Bangalee or the Bengali people, are an Indo-Aryan peoples, Indo-Aryan ethnolinguistic group originating from and culturally affiliated with the ...
,
Sinhalese
Sinhala may refer to:
* Something of or related to the Sinhalese people of Sri Lanka
* Sinhalese people
* Sinhala language, one of the three official languages used in Sri Lanka
* Sinhala script, a writing system for the Sinhala language
** Sinha ...
, among other groups in eastern and southern South Asia),
Nilotes
The Nilotic peoples are people indigenous to the Nile Valley who speak Nilotic languages. They inhabit South Sudan, Sudan, Ethiopia, Uganda, Kenya, the Democratic Republic of the Congo, Rwanda, Burundi and Tanzania. Among these are the ...
,
Cushites and
Amazigh
, image = File:Berber_flag.svg
, caption = The Berber ethnic flag
, population = 36 million
, region1 = Morocco
, pop1 = 14 million to 18 million
, region2 = Algeria
, pop2 ...
people.
Perception and attribution
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 clinally across Eurasia. Its use, therefore, as a
phenotypic
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
marker to define biological populations is debatable.
Possible evolutionary function
![Jens Byggmark Schladming 2008](https://upload.wikimedia.org/wikipedia/commons/9/99/Jens_Byggmark_Schladming_2008.jpg)
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
Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet (UV) rays from either natural (e.g. intense sunlight) or artificial (e.g. the electric arc during welding) ...
. Though its appearance in peoples of Southeast Asia can be linked to possible descent from cold-adapted ancestors, its occurrence in various African peoples is not open to this explanation. The epicanthic fold found in many African people has been tentatively linked to protection for the eye from the high levels of
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
light found in desert and semi-desert areas.
The exact evolutionary function and origin of epicanthic folds remains unknown. Scientific explanations include either random variation and selection (presumably
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
), or possible adaption to desert environment and/or high levels of ultraviolet light found in high-altitude environments, such as the
Himalayas
The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
.
A cold-adaptive explanation for the epicanthic fold is today seen as outdated by some, as epicanthic folds appear in some African populations. Dr. Frank Poirier, a physical anthropologist at Ohio State University, concluded that the epicanthic fold in fact may be an adaptation for
tropical region
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
s, protecting the eyes from overexposure to ultraviolet radiation, and was already part of the natural diversity found among early modern humans.
Other factors
Age
Many
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
es lose their epicanthic folds after three to six months of gestation. Epicanthic folds may be visible in the development stages of young children of any ethnicity, especially before the nose bridge fully develops.
Medical conditions
Epicanthic fold prevalence can sometimes be found as a sign of congenital abnormality, such as in
Noonan syndrome
Noonan syndrome (NS) is a genetic disorder that may present with mildly unusual facial features, short height, congenital heart disease, bleeding problems, and skeletal malformations. Facial features include widely spaced eyes, light-colored ...
and
Zellweger syndrome
Zellweger syndrome is a rare congenital disorder characterized by the reduction or absence of functional peroxisomes in the cells of an individual. It is one of a family of disorders called Zellweger spectrum disorders which are leukodystrophie ...
. 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
Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
(also known as trisomy 21) have prominent epicanthic folds.
In 1862,
John Langdon Down
John Langdon Haydon Down (18 November 1828 – 7 October 1896) was a British physician best known for his description of the genetic condition now known as Down syndrome, which he originally classified in 1862. He is also noted for his work in ...
classified what is now called Down syndrome. He used the term ''mongoloid'' for the condition. This was derived from then-prevailing ethnic theory
and from his perception that children with Down syndrome shared physical facial similarities (epicanthic folds) with those of
Blumenbach
Johann Friedrich Blumenbach (11 May 1752 – 22 January 1840) was a German physician, naturalist, physiologist, and anthropologist. He is considered to be a main founder of zoology and anthropology as comparative, scientific disciplines. He wa ...
's
Mongolian race. While the term "mongoloid" (also "mongol" or "mongoloid idiot") continued to be used until the early 1970s, it is now considered pejorative and inaccurate and is no longer in common use since the 1970s about such medical conditions.
In
Zellweger syndrome
Zellweger syndrome is a rare congenital disorder characterized by the reduction or absence of functional peroxisomes in the cells of an individual. It is one of a family of disorders called Zellweger spectrum disorders which are leukodystrophie ...
, epicanthic folds are also prominent.
Other examples are
fetal alcohol syndrome,
phenylketonuria
Phenylketonuria (PKU) is an inborn error of metabolism that results in decreased metabolism of the amino acid phenylalanine. Untreated PKU can lead to intellectual disability, seizures, behavioral problems, and mental disorders. It may also resu ...
, and
Turner syndrome
Turner syndrome (TS), also known as 45,X, or 45,X0, is a genetic condition in which a female is partially or completely missing an X chromosome. Signs and symptoms vary among those affected. Often, a short and webbed neck, low-set ears, low hair ...
.
See also
*
Blepharitis
*
Epicanthoplasty
Epicanthoplasty is a rare eye surgery to modify the epicanthal folds. It can be a challenging procedure because the epicanthal folds overlay the lacrimal canaliculi (tear drainage canals).
Although an epicanthic fold can also be associated with a ...
, the surgical modification of epicanthic folds
*
Human physical appearance
Human physical appearance is the outward phenotype or look of human beings.
There are infinite variations in human phenotypes, though society reduces the variability to distinct categories. The physical appearance of humans, in particular those a ...
References
External links
*
{{Authority control
Human eye anatomy
Facial features
Skin anatomy
Eye