Epicanthic fold

Epicanthic fold

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Epicanthic fold

Eyes with epicanthic fold (inner sections) 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 term "epicanthic fold" refers to a visually categorized feature; however, there are different underlying causes.

Population distribution
Conditions underlying expression

Adaptive Significance

Children
Inheritance
Surgical alteration
See also
References

Footnotes
Notations

External links

Population distribution

The epicanthal fold occurs in people of Central Asian and East Asian descent, such as Kazakhs, Mongols, Hazaras, Chinese, Koreans, Japanese, Vietnamese and some South and Southeast Asians like Burmese, Filipino, Cambodian, Thai, Bhutanese, Northern Nepali, Tibetans, Ladakhis and others. It also occurs in Inuit, Native Americans, Afro-Asians, Khoisans (Capoids) in Africa and Madagascar, and certain groups from southern Sudan such as the Dinka and the Nuer. It can also occur among the Sami people.

The epicanthic fold occurs more frequently among persons of East Asian descent than among southeast Asians or south Asians. Epicanthic folds are not uniform in appearance or in the extent to which the fold covers the eyelid, and certain populations will tend to a more or less developed fold.

Conditions underlying expression

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) express this trait.

The causes for the expression of epicanthic folds may be ethnic background (including but not limited to low genetic diversity characteristics caused by inbreeding depression, pedigree collapse, cultural isolation, endogamy, etc.) or medical conditions (epicanthic folds are also a characteristic of Down Syndrome and Cri du chat, two chromosomal abnormalities that are associated with severe mental retardation).

Adaptive Significance

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 savannah and deserts, and the theory is that an epicanthic fold in such an environment would expose a narrower section of the eye to incoming light, reducing the amount of light entering the eye. The trait may also be useful against strong winds.^[1]. Regarding 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.

Inheritance

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

There are numerous populations across the world, like Caucasians, many Africans and South Americans which lack an epicanthic fold. Children who have one parent with a pronounced epicanthic fold and one without can have varying degrees of epicanthic .

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.

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.