The epicanthal fold occurs in most people of East Asian descent including Mongols, most Central Asians, Chinese, Koreans, Japanese, Vietnamese and other ethnic groups of East Asian and Southeast Asian origin such as Indonesians, Filipinos, Malaysians, Inuit, Native Americans, Afro-Asians, Khoisans (Capoids) in Africa and Madagascar, and certain groups from southern Sudan (e.g., the Dinka and the Nuer). Epicanthic folds may also be seen in young children of any race before the bridge of the nose begins to elevate. The epicanthic fold occurs more frequently among persons of East Asian descent compared with southeast Asians or south Asians. Epicanthic folds are not uniform in their appearance and/or in the extent to which the fold covers the eyelid. Certain populations show tendencies to have the fold more developed (Han Chinese for example) while other populations show a tendency for the fold to be less developed (Koreans for example).
The term "epicanthic fold" refers to a visually categorized feature; however the underlying cause of its expression in any given individual may be entirely different.
Conditions underlying expression
The causes for the expression of epicanthic folds depend upon a person's ethnicity and/or medical condition. For instance it is normal for the majority of certain people of African descent (ex. the Khoisan and the Dinka) as well as Asian descended peoples (particularly East and Southeast Asians) to express this trait. However, if the epicanthic fold occurs in populations that don't usually express it a person is a mixture of an epicanthic and some other non-epicanthic group, expression could result from inheritance.Adaptive Significance
One hypothesis as to why epicanthic folds came about implicates the climates in which populations expressing them arose. Specifically, in the case of those who are of central East Asian descent, the abundant snow that accumulates in this area (ex. Mongolia and/or Siberia) may have played a role in their development. Given that the intensity of sunlight is enhanced when it reflects off of light colored surfaces (such as white snow), the adaptive advantage of expressing an epicanthic fold in such an environment would be that the exposure of a narrower section of the eye to incoming light would serve to protect more of the eye from its intensity. The trait may also be useful against strong winds.. With regards to the Khoisan in Africa, it is likely that the epicanthic fold was acquired for analogous reasons. Specifically, in the vast dry grasslands of the Savannah regions, the yellow grasses also reflect and intensify sunlight. Additionally, analogous conditions are present in the case of the little mentioned epicanthic folds of Saharan groups such as the Dinka or Nuer of Sudan (Hassan, 1962) who live in environments in which sunlight reflects off of the light colored sands of the desert.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.
Inherited
There are numerous populations, across the world, that lack an epicanthic fold. However, the epicanthic fold is common in people of many, though not all, groups of East Asian and Southeast Asian descent. It is found in significant numbers amongst Native Americans, the Khoisan (Capoids) of Southern Africa, many Central Asians and some people of Scandinavian , Hungarian and Sami origin. It also present on people of Tibetan descent, especially Tibetans and North-East Burmese people. Children of a parent with a pronounced epicanthic fold and one without an epicanthic fold may have varying degrees of epicanthic folds.
In 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 and not the other, or neither.
Surgical alteration
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.See also
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Last updated on Friday July 25, 2008 at 16:38:16 PDT (GMT -0700)
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