The single eyelid refers to the smooth skin between the lower edge of the eyebrow arch of the upper eyelid and the palpebral margin without folds. When people open their eyes, the eyelid without folds is commonly known as the single eyelid. The double eyelid has a shallow groove on the upper eyelid skin, which allows the lower skin to move up when the eyes are opened, while the upper skin relaxes and folds down to form horizontal skin folds, which is often called the double eyelid.
In most people's cognition, the difference between double eyelids and single eyelids is obvious. In fact, there are aesthetic, morphological and anatomical differences between the single eyelid and the double eyelid.
The state of human single eyelid and double eyelid is closely related to heredity and generally remains unchanged throughout life. But there are also a few people who will change with age. Some people in adulthood, the original single eyelids will gradually become double eyelids; Some people's eyelid skin sags due to aging, covering the original fold of double eyelid, thus presenting a single eyelid appearance. In the shape of double upper eyelids, most people are symmetrical on both sides, but about 2.85% - 8.89% of people are not consistent on both sides, one side is a single eyelid, and the other side is a double eyelid.
As far as the eastern nations are concerned, the single eyelid and double eyelid are two different eyelid shapes. From a physiological point of view, they are both normal and basically have no difference. However, from an aesthetic point of view, single eyelids often give people a feeling of small eyes and "not beautiful enough". Functionally, double eyelids are more able to express emotions and show bright eyes than single eyelids. Binocular fold cosmetic surgery can not only increase aesthetic feeling, but also has practical functional significance, which is also the main reason for the extensive development of bilateral fold surgery.
From the morphological point of view, the main difference between single eyelid and double eyelid is whether there are transverse folds on the upper eyelid. The upper eyelid skin of the single eyelid is thick and appears to be relatively bloated. The skin is slightly drooping and covers the eyelid margin. The root of the eyelashes cannot be seen when you look flat; On the other hand, the upper eyelid skin of the double eyelid is thin and delicate, the skin does not droop, and the palpebral margin is all visible. The palpebral fissure of single eyelid is short and narrow, while that of double eyelid is long and wide. The eyelashes of the single eyelid are short and sparse, and they tend to tilt downward when looking at head up, sometimes even cover the pupil, affecting the field of vision and vision; The eyelashes of the double eyelids are longer, and the eyelashes are slightly upwarped when looking straight up. In the shape of the eye corner, the inner canthus of the single eyelid is often rounded with epicanthus, while the inner canthus of the double eyelid is generally sharp and without epicanthus.
Due to the influence of race, region, heredity, age and other factors, there are significant differences in morphology and anatomical structure between single eyelid and double eyelid. The skin of single eyelid is thicker, the subcutaneous tissue is higher, the orbicularis oculi muscle is developed and there is more fat behind the orbicularis oculi muscle; The opposite is true for double eyelids. The position of the orbital septum of the single eyelid is low and the orbital septum fat may be prolapsed on the upper edge of the tarsal plate or in front of the tarsal plate; However, the orbital septum of the double eyelid is at a higher position without prolapse. The differences of these anatomical structures lead to the single eyelid shape which can not form folds when opening the eyes; Because of the characteristics of the anatomical structure, the double fold can be formed when the eyes are opened and the shape of the double fold appears as the double fold.
Binocular eyelid surgery, which is often mentioned, is actually a process of modifying and restructuring the anatomical structure of a single eyelid by means of surgery based on aesthetic principles to form the appearance of the eyelid. This kind of operation can not only make the eyes look more beautiful, but also improve the functional performance of the eyes to a certain extent, which is one of the important reasons for the wide acceptance and development of double eyelid surgery.
