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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. This is a normal trait for a large percentage of humans. 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 are rounder.

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

Other names for this trait include plica palpebronasalis, palpebronasal fold, and Mongolian eye fold.

Conditions underlying expression

Evolutionary

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. The trait may also be useful against strong winds and cold weather such as the ones on the Central Asian steppes. For instance the country of Mongoliamarker is hot in the summer and extremely cold in the winter, with January averages dropping as low as -30°C (-22°F). The country is also subject to occasional harsh climatic conditions known as zud. The capital Ulaanbaatarmarker 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 who live in environments in which sunlight reflects off the light colored sands of the desert.

Population distribution

The epicanthic fold can occur among people of North Asian, Central Asian, East Asian and Southeast Asian descent, such as the Mongols, Chinese, Koreans, Japanese, Vietnamese, Kazakhs, Hazaras, and some other Asian ethnic groups like Burmese, Bangladeshismarker, Filipinos, Cambodians, Malays, Thais, Bhutanese, northern Nepalis, Tibetans, Ladakhismarker, and the inhabitants of North Eastern India (for example, the Mizo and the Garo), among others. Mixed race people of partially Asian descent, such as Eurasian and Afro-Asians may inherit epicanthic folds.

Epicanthic folds are also common among Native Americans and Inuit. They can also be found inherited among some Oceanic peoples including Tongans, Samoans, Micronesians and Hawaiians.

Some African ethnic groups also have epicanthic folds; these include the Khoisans (Capoids) in Africa and certain groups from southern Sudanmarker such as the Dinka and the Nuer.

Epicanthic folds are also found in a minority of Europeans having no known Asian background, especially in eastern Europe and across northern Europe in areas such as Scandinavia.

Medical



Epicanthic folds appearing on individuals from ethnic groups that do not traditionally display the characteristic, especially when combined with other symptoms, can be a sign of a number of disorders. These include the chromosome abnormalities associated with Down syndrome, Cri du chat syndrome, Williams syndrome, and Triple-X syndrome as well as fetal alcohol syndrome, Ehlers-Danlos syndrome, and 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.

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



References

  1. Hassan, M. (1962) “Mongolism in Sudanese Children”, J Trop Pediatr. 8: 48-50
  2. MedlinePlus Medical Encyclopedia


External links




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