1. Causes of scar formation: 1. Surgical instruments have caused too much damage to the tissue: the thickness of the upper eyelid is only 3-5 mm, but ordinary doctors use backward surgical instruments, and the traditional surgical methods are one-size-fits-all, which completely destroys the structure of the tissue and cannot avoid the damage to nerves, blood vessels and lymphoid tissues. The repair of postoperative tissue fibrosis will cause a wider scar. 2. Rough anatomy: Many doctors can't clearly reveal the organizational structure of each layer during the operation, and even some doctors can't tell the anatomical level of the upper eyelid at all. Most doctors are used to cutting off too much subcutaneous soft tissue, which will lead to blurring at the tissue level. The upper and lower tissue layers are different in thickness, and tissue adhesion and fibrous tissue hyperplasia are easy to occur after operation, and wide scars or uneven scars are easy to form after operation. 3. Rough suture: The traditional suture method only fixes the skin on the tissue in front of the meibomian without treating the subcutaneous and muscle, which is easy to cause subcutaneous adhesion and obvious scars. Moreover, the traditional suture method has too large spacing and irregular incision, and the proliferated fibrous tissue is easy to produce wider scars. Second, the repair method and effect: As far as the double eyelids are concerned, in order to improve the scar situation, it is necessary to design the surgical incision plan according to the specific situation, such as the height of the double eyelids, the position of the scar, and the shape of the double eyelids. It is worth noting that some secondary repair operations can only improve the surgical effect, but can not achieve the perfect design of the first time.