The medial canthus is a vertically oriented curved skin fold through the medial canthus, mostly bilateral, associated with genetics and nasal development, and can be seen as part of normal development prior to midface expansion (. The medial canthus often continues downward from the upper lid, but is less common upward from the lower lid, and is particularly noticeable in children with a low nasal bridge. It may occur alone or as part of a syndrome with other abnormalities. As the medial canthus obscures the tear trough and medial canthus to varying degrees, it has a greater impact on appearance and can impede horizontal vision in severe cases. 1. Etiology: The occurrence of medial canthus is closely related to genetics, age, race and other factors. Genetic factors: congenital canthus is inherited in an autosomal dominant manner, and is particularly pronounced in those with narrow lid syndrome, with a tendency to worsen in the process of passing on the disease. Age: Canthus is the norm in fetal life and disappears with the development of the nasal bridge. The incidence is greatest in childhood and decreases with age. Racial factors: Canthus is more common in the yellow race and is common in the Mongolian race of East and North Asia. Black people often have no medial canthus, and white people are less common. 2, typology and clinical manifestations: canthus can be divided into congenital and acquired canthus according to the cause of occurrence. Congenital canthus: It is more common clinically and is generally bilateral. If the canthus is not accompanied by other eye abnormalities, it is a simple canthus; if it is accompanied by a small lid fissure, ptosis, or widened inner canthus, it can be seen as a narrow lid fissure syndrome; some are accompanied by other eye development abnormalities such as small eyeballs. The congenital canthus can be divided into four types, namely brow, lid, lid and inverted canthus, according to its shape and direction. The brow-shaped canthus starts at the brow and extends downward to the skin of the tear sac; the lid-shaped canthus starts at the upper lid plate area and extends downward through the inner canthus to the lower lid margin, sometimes fusing with the nasal cheek crease; the platysmal canthus starts at the anterior lid plate area of the upper lid and gradually disappears downward into the inner canthus, which is a common eyelid pattern in Asians; the inverted canthus starts at the lower lid and extends upward through the inner canthus. This is a common Asian eyelid pattern; the inverted canthus, which begins in the lower lid and extends upward through the medial canthus to the upper lid, partially covering the medial canthus. Acquired canthus: most often seen in the inner canthus from cuts, burns, and scar traction after surgery on the inner canthus, mostly unilateral. 3. Treatment: Eyebrow, lid, and lid canthus may reduce or disappear with age, and childhood canthus generally does not require surgery. In the past few years, more and more patients have undergone endophthalmos correction surgery due to cosmetic needs, especially with simultaneous double lid surgery, which can result in significant improvement in eye shape. Those with combined ptosis and narrow lid fissures, especially those with inverted canthus, will not disappear with age and can be operated on earlier than 2-3 years of age. If the canthus is accompanied by inversion of the lower eyelid and photophobia and tearing, surgery should be performed early if conservative treatment is not effective. Acquired canthus should be operated 6 months after the scar has softened and stabilized. 4.Surgical methods and indications: At present, it is believed that the canthus is due to excessive tension in the vertical direction of the skin of the inner canthus, resulting in longitudinal skin folds in the inner canthus, and local flap transposition is used to relieve the tension of the skin in the vertical direction. The commonly used procedures are “L” shaped skin excision, “Z” shaping, “Y-V” shaping, and Mustarde method. 5.”L”-shaped skin excision: It is suitable for mild inverted type canthus. An oblique lower lid incision is made along the crease from the upper end of the redundant skin, extending to the center of the lower lid, 2 to 3 mm from the lower lid margin, separating the subcutaneous tissue, and pulling the skin of the lower lid margin incision close to the medial canthus down to the nose until the redundant skin disappears to determine the amount of skin to be removed. 6.”Z” surgery: There are single “Z” surgery and double “Z” surgery. Single “Z” surgery is suitable for mild canthus, including Stallard and Fox “Z” surgery. A line is drawn along the full length of the longitudinal axis as the medial axis of the “Z” flap, with a short line perpendicular to the upper lid margin at the upper end of the line and a short line angled inward and upward at the lower end of the line as the two arms of the “Z” flap. The skin is incised along the line, subcutaneously separated, and the flap is transposed and intermittently sutured. Double “Z” canthoplasty is suitable for more severe canthopexy, and can also correct inverted canthopexy with Spaeth double “Z” and Blair double “Z”. The “Y-V” canthopexy can also be corrected. 7.”Y-V” surgery: It is suitable for more serious canthal redundancy and those with widened inner canthal spacing. The two arms of the “Y” are parallel to the upper and lower lid margins, and the nasal end of the long axis is the new medial canthus, the length of which depends on the extent of the medial canthus. The incision is separated subcutaneously and the two arms of the “Y” are pulled to the nasal side and sutured to the nasal end of the long axis to make a “V” shape. If there is a widening of the medial canthus, a shortening or folding of the medial canthal ligament may be performed.