Epicanthic fold

An epicanthic fold is when the skin of someone's eyelid folds on the inner corner of the eye. There are different types of epicanthic folds. They can be caused by genetics, ethnicity, age, or mental conditions. 

 Types 
There are four types of epicanthic folds:

 Epicanthus supraciliaris is a vertical fold that goes from above the eyelid to the caruncle. 
 Epicanthus palebralis is when the fold is prominent on both eyelids. This type is the most common overall. 
 Epicanthus tarsalis is when the fold is most prominent on the upper eyelid. This type is most common in East Asians.
 Epicanthus inversus is when the fold is most prominent on the lower eyelid.

 Ethnicity distribution 
Epicanthic folds are usually associated with Asians. This mostly includes East Asians, but can also include North Asians, Southeast Asians, and Central Asians. However, non-Asians can have epicanthic folds too. This can include Khoisans, Polynesians, the Sami, the Finnish, Micronesians, and Native Americans.

Other groups like Jews and some African groups like the Amazigh, Cushites, and Nilotes can also have epicanthic folds. However, it is much less common. Some European ethnicities can have epicanthic folds too. However, most of the time, if some of European ancestry has epicanthic folds, it is because of a genetic disorder.

 Causes 
Epicanthic folds are caused when someone has too much fat or skin around the eye. The reason why this happens is not fully known. Some guesses include that epicanthic folds help people in hot climates from sun blindness or people in cold climates from snow blindness.

Most fetuses have epicanthic folds, but lose them around three to six months while forming. Many young children of any ethnicity have epicanthic folds, but they may go away while developing.

Some medical conditions can cause epicanthic folds. This includes Down syndrome, Turner syndrome, Williams syndrome, Noonan syndrome, and fetal alcohol syndrome. About 60% of people with Down syndrome have epicanthic folds.

 References 

Category:Eye anatomy
Category:Eye
Category:Skin