Excimer laser for myopia, hyperopia and astigmatism Excimer laser keratomileusis (PRK) This is a fast developing keratomileusis procedure in recent years, commonly used fluorinated argon excimer laser, output 193nm ultraviolet laser, the energy of each photon in its beam is 6.4ev, which is higher than the energy of intermolecular connection of cornea (3.5ev). energy (3.5ev). Therefore, the excimer laser can be applied to cut the surface of the corneal optical zone according to a pre-set procedure. The deeper the cut, the greater the post-operative refractive power correction, but the greater the chance of complications. It is now mainly used to correct myopia below -6.0D. The results for high myopia are not as good as those for mild and moderate myopia, and there is an increased chance of complications such as regression and corneal haze. Excimer laser in situ keratomileusis (LASIK) This procedure is a new method based on PRK and ALK (automated lamellar keratoplasty), in which a corneal flap with a diameter of about 7.2 mm and a thickness of about 160 μm on the nasal side with a tip is first cut on the corneal surface with a lamellar keratome, and then an excimer laser is used in the central area of the cornea. The middle corneal stroma is then cut with an excimer laser in the central area. After surgery, the tipped flap is repositioned without sutures. This procedure preserves the corneal epithelium and anterior elastic layer, which is more in line with the physiological state of the cornea, does not cause corneal clouding after surgery, and increases the range of myopia correction. It is currently the best method to correct high myopia (<15.0D).