epicanthic fold

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A fold of skin of the upper eyelid that partially covers the inner corner of the eye. Also called epicanthus.

In human anatomy, this is the fold of skin covering the inner corner (canthus) of the eye, normally from the top of the eye downward in a semilunar form. The epicanthic (or epicanthal) fold is a normal feature of fetuses of all races but is present in a pronounced form and in high concentrations in humans of certain geographic races and subraces. The epicanthic fold is sometimes referred to as the ‘Mongolian eye fold’, because of its high incidence in and historical association with the Mongoloid (Asian) geographic race. The presence or absence of the epicanthus, which helps produce in Asians a distinctive eye shape and facial appearance, has helped fuel controversies in physical anthropology and evolutionary theory, including historical attempts to establish racial hierarchies based on evolutionary fitness and disputes concerning the nature of evolutionary adaptation. In addition, epicanthic folds in individuals of groups without a high normal incidence of its presence is often phenotypic of genetic or congenital disorders. In some recent debates, the alleged absence of the fold in some depictions and descriptions of humans from Chinese and Indian history has led some Afrocentric historians to claim an African origin of at least some aspects of Indian and Shang dynasty Chinese culture.

In addition to Asians and eastern subarctic and arctic Eurasians, some native American peoples (especially those of Middle America and some populations in South American lowland areas), the Capoid local race of southern Africa, and some of the composite racial groups of Pacific island peoples have high incidence of developed epicanthic folds. The fold occurs less frequently in Southeast Asian populations and in North American Indian groups but occurs occasionally in some European groups, for example in some Scandinavians and Poles.

While epicanthic folds occur more frequently in Asiatic groups and those peoples genetically linked to Asia, its presence is not universal in these peoples and it occurs less frequently in other groups. The incidence of epicanthic folds varies widely among the nine major geographic races and their local races. Attempts to define racial groups by the presence or absence of such features, by phenotype, rather than by genotype and specific inherited traits, are historically problematic and scientifically unreliable. There is substantial variation in phenotype within geographic races and subraces produced by the gene flow inevitable in an aggressively mobile species such as our own, by environmental conditions, and simply by individual variation due to a number of causes, including genetic mutation and the ‘small-sample’ effects of isolated population groups. Modern genetics rejects the notion of a ‘pure’ race; while the historical origins of some geographic groups are obscure, contemporary racial groups are mixtures of the gene pools of many geographic races. Thus, the presence or absence of a developed epicanthic fold, while an indication of one of a number of genetic origins and an important diagnostic feature of certain genetic disorders, cannot bear the cultural freight often bequeathed to it by history, pseudo-science, and prejudice.

The association of the epicanthic fold with Mongolians and Asians more generally served to reinforce notions of racial and cultural supremacy in nineteenth and early-to-mid twentieth century European physical anthropology, physiognomy, and racial theory. Humans with the genetic anomaly now known as Down's syndrome, caused by having three copies (trisomy) of chromosome 21, have limited physical growth and mental retardation of varying severity, and an increased risk of other serious physical problems. Down's syndrome is one of the more common chromosomal defects, occurring on average in 1 in 900 live births. The Down's syndrome infant is quickly recognized by both facial and more general cranial characteristics, including a rounded head, short neck, thin and usually fine hair, flat nose, small mouth, and, especially, slanting eyes with pronounced epicanthic folds.

John Langdon Haydon Down first described this syndrome in 1866 and termed it ‘mongolism’ because of the eyefold and other facial features that Down believed linked the European children he observed to geographic races with a high incidence of such features, including the Asian geographic race (of which the Mongolian people constitute a local race). Down's report on this condition is an important example of the influence of cultural assumptions both on reading facial features and on the construction of anthropological theories designed to categorize and judge peoples: his comparison of European children born with a chromosomal disorder with the normal features of many Mongolians was both scientifically inaccurate as an analysis of the condition and a patronizing mischaracterization of Mongolians. Down argued that these children represented a degeneration of the superior (European) human type, stating that ‘A very large number of congenital idiots are typical Mongols.’ The racial theories used by Down and others have been decisively rejected by modern science, but it is only recently that the descriptions of Down's syndrome as ‘mongolism’ or ‘mongolian idiocy’ and persons with Down's syndrome as ‘mongols’ or ‘mongolian idiots’ have begun to fade from view.

In addition to Down's syndrome, epicanthic folds occur in other, less common genetic disorders, including Trigonocephaly ‘C’ syndrome and two types of ‘Blepharophimosis, Ptosis, Epicanthus Inversus Syndrome’ (BPES). In the latter condition, the epicanthic fold is inverted, extending from the lower eyelid up the side of the nose. Folds also occur in certain congenital conditions, including fetal alcohol syndrome. While the facial anomalies of infants with fetal alcohol syndrome are usually less pronounced than those of a Down's syndrome child, some of the same features occur, including a flat nose and nasal bridge, and developed epicanthic folds.

— Jeffrey H. Barker

A characteristic crease in the eyelid; seen in persons with Down syndrome.

Eyes with epicanthic fold on younger East Asian male

Eye with epicanthic fold on an older East Asian male

An epicanthic fold, epicanthal fold, or epicanthus is a skin fold of the upper eyelid (from the nose to the inner side of the eyebrow) covering the inner corner (medial canthus) of the eye. The trait arises because the eyelid muscles are weaker or lower compared with people who do not have this epicanthic fold, resulting in a lower fold in the eyelid, when the eyes are open. The fold gives the eyes of East Asians a characteristic shape which is narrower and almond-like in comparison to most Westerners, whose eyes appear rounder.

The term "epicanthic fold" refers to a visually categorized feature of the eyelid; however, there are different underlying causes.

Contents 1 Conditions underlying expression 1.1 Evolutionary 1.1.1 Population distribution 1.2 Medical 1.3 In children 1.4 Inheritance 2 Surgical alteration 3 See also 4 References 5 External links

Conditions underlying expression

Evolutionary

Genghis Khan drawn with an epicanthic fold

One hypothesis as to why epicanthic folds came about involves the climates in which populations expressing them arose. Sunlight reflects more intensely off light colored surfaces, such as those prevalent in snowy regions or savannahs and deserts. The theory is that an epicanthic fold in such an environment would protect the eyes from extra UV radiation.^{[citation needed]} The trait may also be useful against strong winds and cold weather such as the ones on the Central Asian steppes.^{[citation needed]} For instance the country of Mongolia is hot in the summer and extremely cold in the winter, with January averages dropping as low as -30°C (-22°F).^[1] The country is also subject to occasional harsh climatic conditions known as zud. The capital Ulaanbaatar has the lowest average temperature of any national capital in the world. Mongolia is high, cold, and windy. It has an extreme continental climate with long, cold winters and short summers, during which most of its annual precipitation falls.

With regard to the vast dry grasslands of the savannah regions, the yellow grasses also reflect and intensify sunlight. Additionally, analogous conditions are present among desert groups such as the Dinka or Nuer of Sudan^[2] who live in environments in which sunlight reflects off the light colored sands of the desert.

Population distribution

The epicanthic fold occurs commonly in people of Central Asian, East Asian and Southeast Asian descent as a result of adaptive significance, such as the Mongols, Hazaras, Chinese, Koreans, Japanese, Vietnamese, Kazakhs and some South and Southeast Asians like Burmese, Filipinos, Cambodians, Malays, Thais, Bhutanese,Northern Bangladeshis, Northern Nepalis, Tibetans, Ladakhis and others. It also occurs in Afro-Asians, Khoisans (Capoids) in Africa and Madagascar, and certain groups from southern Sudan such as the Dinka and the Nuer. Epicanthic folds can also be found inherited among some Oceanic peoples including Tongans, Samoans, Micronesians, and Hawaiians. Many Inuits and some Native Americans may have it as well.

The epicanthic fold occurs more frequently among persons of East Asian descent than among southeast Asians or south Asians.

Medical

Scottish award-winning film and TV actress Paula Sage (left) has the characteristic as one of the medical symptoms of Down syndrome

If the epicanthic fold appears on people who traditionally do not display the characteristic, it can be a sign of a number of disorders coupled with other symptoms like mental retardation, weak muscles, etc.

Epicanthic fold can be a result of low genetic diversity characteristics caused by inbreeding depression, pedigree collapse, cultural isolation, endogamy, etc. or medical conditions like Down syndrome, Cri du chat syndrome and Williams syndrome, three chromosomal abnormalities that are associated with severe intellectual disability. Another condition in which this is seen is Triple-X syndrome, a chromosomal abnormality that does not necessarily impair intelligence. Epicanthic folds can also be caused by fetal alcohol syndrome,^[3] Ehlers-Danlos syndrome and/or pre-term birth.

In children

All humans initially develop epicanthic folds in the womb. Some children lose them by birth, but epicanthic folds may also be seen in young children of any ethnicity before the bridge of the nose begins to elevate. They may persist where birth is pre-term, and sometimes also where the mother is alcoholic.^[4]

Epicanthic folds can cause a child's eyes to appear crossed, a scenario known as pseudostrabismus.

Inheritance

A man from a mixed race background with an epicanthic fold.

Children who have one parent with a pronounced epicanthic fold of non-medical reason and one without can have varying degrees of epicanthic fold.

Surgical alteration

In some Asian ethnicities, the presence of an epicanthic fold is associated with a less prominent upper eyelid crease, commonly termed "single eyelids" as opposed to "double eyelids". The two features are distinct; a person may have both epicanthic fold and upper eyelid crease, one or neither.

The procedure of reducing or removing epicanthic folds is epicanthoplasty. It is now an extremely rare procedure. Asian blepharoplasty, however, is a popular form of cosmetic surgery in East Asia. The use of "eyelid glue" or "eyelid tape" (sometimes referred to as "eye glue" or "eye tape") is used to create the appearance of the "double eyelid" by finding a "natural fold" in the eyelid and tucking it in and holding it with an adhesive.

See also

• Human physical appearance

References

1. ^ "Republic of Mongolia" (PDF). 2004. http://www.imcg.net/gpd/asia/mongolia.pdf. Retrieved on 2008-02-10. 
2. ^ Hassan, M. (1962) “Mongolism in Sudanese Children”, J Trop Pediatr. 8: 48-50
3. ^ MedlinePlus Medical Encyclopedia
4. ^ "Ophthalmic Involvement in the Fetal Alcohol Syndrome: Clinical and Animal Model Studies". Journal of Alcohol and Alcoholism. http://alcalc.oxfordjournals.org/cgi/content/full/37/1/2. Retrieved on 16 November 2007. 

External links

• Mother-daughter comparison photos
• Drawing of male face
• Drawing of female eye

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