Single eyelid refers to the smooth skin between the lower edge of the eyebrow arch of the upper eyelid and the eyelid margin. When the eyes are opened, no wrinkles are formed, which is called single eyelid, commonly known as single eyelid. Double eyelid means that the skin of the upper eyelid has a shallow groove above the eyelid margin. When you open your eyes, the skin under this groove moves upward, while the skin above this groove hangs loosely at the double eyelid groove and folds down into a horizontal fold, which is called double eyelid. In people's minds, the difference between double eyelids and single eyelids is obvious. In fact, there are aesthetic differences, morphological differences and anatomical differences between them. & lt/P & gt； & ltP> The single eyelid and double eyelid of human beings are related to heredity and generally remain unchanged for life. But a few people change with age. Some gradually become double eyelids as they grow up to adulthood; Some are aging and drooping eyelid skin, which covers the folds of the original double eyelids and gives people the appearance impression of a single eyelid. People's double eyelids are generally symmetrical in shape, but about 2.85%-8.89% people have different double eyelids, showing that one side is a single eyelid and the other is a double eyelid. For orientals, single eyelid and double eyelid are two different eyelid forms. Physiologically, both of them are normal, and there is basically no difference. But from an aesthetic point of view, single eyelids often give people the feeling that their eyes are small and "not beautiful". Functionally, it is not as good as double eyelids to express emotions and show bright eyes. Therefore, double eyelid plastic surgery can not only add aesthetic feeling, but also have certain functional significance in a sense, which is also the main reason for double eyelid plastic surgery. & lt/P & gt； & ltP> From the morphological point of view, the difference between single eyelid and double eyelid is that the skin of the whole upper eyelid is thick and bloated, and the skin is slightly drooping, covering the edge of eyelid, and the root of eyelashes can't be seen when looking up. The upper eyelid skin is thin and delicate, the upper eyelid skin is not drooping, and the eyelid edge is all visible. The palpebral fissure of single eyelid is short and narrow; The palpebral fissure of double eyelids is longer and wider. The eyelashes of a single eyelid are short and sparse. When looking up, they tend to lean down. Sometimes eyelashes will cover the pupils, affecting vision and vision. People with double eyelids have long eyelashes and slightly upturned when they look up. The corner of a single eyelid is rounded because it is often accompanied by epicanthus; The inner canthus of patients with double eyelids is generally sharp, and there is generally no epicanthus. & lt/P & gt； & ltP> Because the occurrence of single eyelid and double eyelid is influenced by race, region, heredity, age and other factors, there are obvious differences in morphology, so there are also obvious differences in anatomical structure. The skin of single eyelid is thicker, the subcutaneous tissue is higher, the orbicularis oculi muscle is more developed, and there is more fat behind the orbicularis oculi muscle. The tarsal plate of single eyelid is thin and narrow, and the levator palpebralis muscle with open eyes is underdeveloped; Double eyelids are just the opposite. The orbital septum position of single eyelid is generally low, and the orbital septum fat can prolapse on the upper edge of eyelid plate or in front of meibomian, while the orbital septum position of double eyelid is high, and there is no orbital septum fat prolapse on the upper edge of eyelid plate or in front of meibomian. Based on the anatomical structure, when the eyelid is open, the skin and orbicularis oculi muscle in front of the tarsal plate can't be lifted together with the tarsal plate, so the upper eyelid can't be folded, showing a single eyelid. When the double eyelids are opened, the skin and orbicularis oculi muscle below the double eyelid line in front of the meibomian can be lifted together with the meibomian, so wrinkles appear on the upper eyelids, showing double eyelids. & lt/P & gt； & ltP> From the perspective of the difference between single eyelid and double eyelid, double eyelid surgery, which people often mention, is actually to modify and reorganize the anatomical structure of single eyelid by surgical means according to aesthetic principles, and finally form the appearance of double eyelid.