The excimer laser currently used in keratomileusis is a 193 nm wavelength laser produced by a mixture of argon fluoride (ArF) gas, which is an ultraviolet cold laser. Each photon has a very high energy and acts on biological tissues not by thermal but by photochemical effects, which means that the laser can break the chemical bonds of biological tissues directly and vaporize the molecules of tissue cells, thus achieving a high cutting precision. The excimer laser is a cold laser that produces very little thermal effect (or some thermal effect if the laser frequency is very high), so it only acts on the tissue at the irradiated site and has essentially no effect on the tissue outside the irradiated area. These characteristics make the ArF laser the ideal laser for refractive eye surgery. The ArF gas mixture produces an excimer laser with a wavelength of 193 nm that can ablate 0.2 microns of corneal tissue per pulse when treating refractive errors. Since there are different types of refractive errors such as myopia, hyperopia and astigmatism, the design of the corneal cutting pattern is also determined by the refractive error. For example, to correct myopia, the tissue in the central zone of the cornea is cut so that the curvature of the cornea in the central zone is reduced, and the depth of the corneal tissue cut is determined by the degree of myopia and the diameter of the selected optical zone.