Eye folds
Eye folds or Epicanthic folds, also known as slanty eyes, are skin folds that cover the inner corner of the eye. This morphological feature is present in about half of the world's population to some degree. It is strongly associated with Mongoloid ancestry, although there are different types of folds stemming from different geographical locations. About 60% of people with Down Syndrome have extremely prominent epicanthic folds[1].
Types of eye folds
The Mongolian, Indian, and epicanthus folds are prevalent in people with Mongoloid (Northeast/Southeast Asian and Amerindian) ancestry. The Hottentot fold is most common among the Khoisan people, and to a smaller degree among Mongoloids and Nordic people with some Mongoloid ancestry. The Negroid and Nordic folds are almost exclusively present among Sub-Saharans (especially the Nilotic people) and North Europeans respectively.
Evolutionary function
As it is most common among peoples who historically lived in harsh cold climates, it is believed that the function of the eye folds was to protect the eyes from freezing winds and snow blindness. However, being also common among some Africans in desert areas has led to the belief that protection against ultraviolet light, prominent in high altitudes (Himalayas) and hot deserts (Kalahari desert for the Khoisan people) may also play a role.
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