The biggest benefit of laser surgery is the short procedure time and the fact that it reduces bleeding from the wound, but the drawbacks are the burns to the tissues adjacent to the lesion and the postoperative scarring. Burning of tissues adjacent to the lesion and postoperative scarring may be insignificant in many parts of our body, but the blow to the delicate vocal cords can be fatal. Before we talk about indications for laser surgery, it is necessary to briefly review the structure of the vocal folds and the histologic properties of the disease. The five tissue layers of the vocal folds, from superficial to deep, are: the epithelium, the superficial lamina propria, the middle lamina, the deep lamina, and the muscular layer of the vocal folds (Muscel). The epithelial and superficial layers of the lamina propria form the mucosa, and the middle and deep layers of the lamina propria form the ligament. Each of these layers of tissue has a predisposition to disease. For example, lesions in the epithelial layer include vocal cord leukoplakia and recurrent papillomas of the respiratory tract. Diseases occurring in the lamina propria usually include vocal polyps, vocal nodules, and vocal Z swellings. Tumors are often trans-laminar, except for carcinoma in situ. This relationship between lesions and tissues dictates that the treatment of different types of disease can be quite different. (1) Epithelial layer The epithelial layer can be divided into two parts, one part covers most of the tissues of the vocal folds, but when vibrating this part of the vocal folds are not in contact with each other and consists of pseudocomplex ciliated columnar epithelium. It is a typical epithelial tissue of the respiratory system, and has the function of mucus secretion, which can help to lubricate the free edge part of the epithelial tissue that is in contact with the vocal folds when they vibrate. The other part of the epithelial layer, which contacts the vocal folds when they vibrate, consists of a complex layer of squamous epithelial cells that counteracts any damage that the vocal folds may cause to themselves when they vibrate in contact with each other. The entire epithelial layer is the thinnest of the five layers, with only about 6-8 layers of cells, and resembles a flexible pod of cells that wrap around the other major internal structures of the vocal folds. The deeper epithelial cell layers form a limbic membrane to distinguish them from the lamina propria beneath. The epithelial layer has almost no mass and is completely dependent on the movement of the vocal folds, with a thin layer of slippery mucus on its surface acting as a lubricant to optimize vibration. (2) The lamina propria The three layers of tissue beneath the epithelium together form the lamina propria. This layer consists of loose extracellular tissue including specialized proteins, carbohydrates and lipids. The superficial lamina propria, composed of loose fibrous tissue and intercellular matrix, contains very few fibroblasts, mainly elastic fibers. Although the superficial lamina propria is as pliable and loose as the epithelial layer, it is slightly denser than the epithelial layer and is soft and gelatin-like in nature, allowing it to vibrate more significantly during articulation. When the flexibility and integrity of this layer is compromised, the waveform of vibration is significantly affected. The gap with the middle layer of the lamina propria is called Reinke’s gap. The middle layer of the intrinsic layer is located on the deep side of the superficial layer of the intrinsic layer and has a clear boundary with the superficial layer. The elastic fibers that make up the interlayer are flexible and can stretch to approximately twice their original length. Although the middle layer of the intrinsic layer is relatively heavy, it still vibrates significantly during articulation. The deeper layer of the lamina propria, which consists mainly of collagen fibers, is rich in fibroblasts. The deep lamina propria is relatively dense and, together with the middle lamina propria, is called the acoustic ligament. These layers of tissue are not present in the neonatal period and only begin to appear in children between the ages of 1 and 4 years. The vocal ligaments continue to develop in childhood until the entire larynx matures at puberty. (3) Vocal Muscle Layer The vast majority of the vocal fold tissue consists of the vocal muscles, and the presence of the vocal muscle layer ensures the tone, stability, and quality of the vocal folds. Unlike the transition between the epithelium and the superficial lamina propria, the deep lamina propria has a special connection with the muscularis propria. The collagen fibers of the deep lamina propria are dispersed among the muscle fibers of the myofibrils of the vocal folds, making the connection between the deep lamina propria and the myofibrils of the vocal folds very strong. This fiber connection makes the linkage between the lamina propria and the myofibrils of the vocal folds much more stable when the vocal folds are vibrating. The muscular layer of the vocal folds is the only one of the five tissue layers that is truly under proprioceptive control due to the distribution of nerves, whereas the epithelial layer and the lamina propria are passively subjected to aerodynamic forces that produce vibration. The muscular layer of the vocal folds is also the part of the vocal folds among the multiple tissue layers that can be truly controlled by the nervous system and tensed or relaxed accordingly. As a result, the vibration of the vocal folds can be affected both by active factors in the vocal folds and by passive effects of aerodynamic factors in that part of the vocal folds, resulting in frequency modification and affecting articulation. For lesions of the epithelial layer of the vocal folds, such as vocal cord cancer, vocal cord leukoplakia, and vocal cord papilloma, because the lesions are located in the epithelial layer of the vocal folds, laser surgery can be appropriate, especially the CO2 laser, which is commonly used nowadays. For polyps and nodules that occur in the lamina propria of the vocal folds, the principle of voice microsurgery is to preserve as much of the epithelial layer of the vocal folds as possible. In this case, the use of laser surgery will inevitably result in a change in the voice or a poor recovery of the voice after the surgery due to the removal of the epithelial layer of the vocal folds that should not have been removed, and the risk of postoperative scars on the normal tissues of the vocal folds due to burns. For lesions of the lamina propria of the vocal folds, such as vocal polyps, vocal nodules and vocal cysts, the current more unified view is still based on microsurgery. Of course, there are some new lasers such as dye laser and KTP laser, which are completely different from CO2 laser.