The medial canthus is a webbed fold of skin in front of the medial canthus from the top down or from the bottom up, and is a characteristic of the Oriental eye. Mongolian fold In both eyelids, the upper eyelid has a fold (called Deckfalte) of different heights parallel to the lower edge of the upper eyelid, which often arises independently from the inner side or from the skin adjacent to it, sloping down toward the nasal skin that originally covered the inner corner of the eye. This special fold is known as the medial canthus. The canthus is less common in Caucasians and more common in Mongolians, 100% in South Chinese, 60-80% in Malaysian natives, 52% in Javanese, and similar to South Chinese in Japanese. Eyelids with medial canthus have an internal fat layer and are therefore thought to display cold-adapted features. The medial canthus used to be called the Mongolian crease. There are two types of canthus: primary and secondary. In primary canthus, there are three types of canthus clinically based on the alignment of the canthus, namely the upper lid type, the inner canthus type, and the inverted type. In primary canthus, if it is accompanied by ptosis, small lid fissure and obvious widening of the inner canthus, it is called eyelid syndrome. A combination of brow deformities is called eyelid-brow syndrome. If there are no other abnormalities, it is called simple canthus. In addition, patients with entropion often have an impingement or even a brow deformity. Secondary canthus is mostly caused by mechanical trauma, burns, infection, and other factors that lead to local scar contracture and pulling, mostly unilateral, and often accompanied by damage to adjacent tissue. Primary canthus is a common and hereditary eye disease, often bilateral, symmetrical in both eyes or varying in severity, mostly seen in Oriental people, especially Mongolians. About 1/3 of our children and toddlers have varying degrees of simple canthus, but as they age and their noses develop, the canthus gradually decreases and tends to stabilize by the age of 10 or so. The effects of canthus: The canthus can conceal the normal shape of the inner canthus and can block part of the vision, affecting the beauty of the eyes. In order to make the eyes more beautiful and appealing, plastic surgery can be used to correct the problem. Treatment of canthus: The purpose of canthus correction is to remove the skin folds in the inner corner of the eye, reveal the tear lake and increase the eye fissure. Treatment is only required if the canthus alone is still evident after puberty. In mild cases, the skin incision can be sutured directly after cutting the redundant skin, while in more severe cases, a “z” reshaping or other flap repair should be performed. Although the incision may be left on the inner canthus after surgery, the surgically enlarged eye canthus will add a lot of color to the eyes.