Many people have moles on their face, with different locations and sizes, but there is a very special type of mole, in which the patient has a mole on each of the upper and lower eyelids. 1. What is the formation mechanism of splitting nevus on the eyelid? Eyelid splitting nevus occurs when the upper and lower lids are not yet separated during the embryonic period, and when the ectodermal lobe of the eye matures and the lid fissure between the upper and lower lids is formed, the nevus is split in two. 2. What is the difficulty in repairing split eyelid nevi? The eyelid is one of the thinnest parts of the human skin. After simple skin graft repair, the skin piece has no subcutaneous fat and often causes varying degrees of ptosis when it adheres to the levator aponeurosis; at the same time, the transplanted skin piece mostly leaves behind pigmentation that is still difficult to resolve, which seriously affects the surgical result. The repair and reconstruction of soft tissue defects in the eyelid area requires not only the repair of the defect but also the restoration of function, which requires that the elasticity, color, texture, and thickness of the grafted tissue be similar or similar to the skin of the eyelid, so a local flap or adjacent flap transfer is the best choice. Temporal and periauricular flaps have the advantage of being hidden in the donor area and can be closed directly, so temporal and postauricular flaps become the best choice for local flaps. 3, What is the best repair option for split eyelid nevus? The orbicularis muscle flap is rich in blood flow, has a large rotation angle, can repair tissue defects in different parts of the upper and lower lids, has a texture and color close to the recipient area, and has enough support to effectively prevent lid ectropion. The flap can be designed as an adjacent or temporal island flap depending on the site, area, and shape of the lesion. The donor-area incision follows the direction of the canthal cortex and is more concealed, but provides a limited flap area, so the orbicularis muscle flap is best suited for small to medium-sized split nevi on the middle and lateral aspects of the eyelid. The donor area of the retrograde superficial temporal artery flap is located in front of the ear, around the earlobe, and is close in texture and color to the eyelid skin, with a sufficiently long tip. The donor area incision is the same as the facial and neck debridement incision line, and is concealed by direct pulling and suturing. The flap is suitable for repairing the medial and lateral lesions of the upper and lower lids, and because of its proximity to the lower lid, it is most suitable for repairing lesions with a large medial and lateral area of the lower lid, with a maximum repair area of 4 cm × 3 cm in this group. the flap can also be made into a parallel flap for simultaneous repair of upper and lower lid defects, and can be used in combination with the postauricular SMAS tip island flap to repair large split nevus skin defects of the lower and upper lids, respectively. The postauricular SMAS-tipped flap is thin and soft, with a maximum donor flap area of 7 cm × 7 cm; the flap tip is sufficiently long, and the ratio of flap width to tip length does not exceed 1:6, so the flap can be viable after surgery. Therefore, the retroauricular island flap is suitable for repairing medial, middle, lateral, and total eyelid skin defects. 4. What are some of the things you must be aware of for repair of split nevus of the eyelid? Once a nevus has involved the lid margin, its removal and repair become very difficult. Once the lid margin is removed, it is difficult to recreate its natural shape, so we strongly recommend that you have the nevus treated as soon as it has not grown into the eyelid. In addition, after the nevus treatment is completed, we recommend that you undergo the necessary adjustment surgery according to the shape of the bilateral eyelids, because the repair of a nevus on the upper eyelid will inevitably affect the shape of the eyelids, and better results will be achieved by bilateral adjustments.