Excimer laser corneal refractive surgery has evolved to the point where, due to improvements in excimer laser therapeutic instrumentation and corneal laminar knives, the surgery has become more accurate and automated, and is more often than not completed in less than 20min. Among all ophthalmic treatments, only excimer laser keratomileusis is currently included in the mandatory requirement for training and licensure, indicating the importance that the government and industry place on this treatment. A qualified practitioner is the key to quality control of the treatment. Each step of the preoperative examination is a screening process for indications for surgery and must be taken seriously; in a sense, the preoperative examination is more important than the surgical operation. 1, medical history Ask about the presence of systemic metabolic diseases and collagenous diseases as well as diseases that must be controlled with long-term medication. Be alert to certain latent diseases, such as diabetes mellitus. Find out whether there are psychoneurological diseases, such as previous depression. Whether you are in a special physiological period, such as pregnancy and breastfeeding, due to hormonal instability in the body, which affects the stability of the refractive error. Some diseases should be avoided during the active period, because of the possibility of delayed corneal wound healing or corneal lysis, as well as vision regression, corneal clouding and other conditions may occur. Ocular history should include acute and chronic inflammatory and other diseases that affect vision, history of eye surgery, and certain eye diseases such as dry eye should be treated in advance. Prolonged contact lens wear may lead to corneal inflammation, corneal hypoxia, dry eye, corneal deformation and corneal limbal neovascularization. In order to avoid the error of preoperative refractive examination, intraoperative bleeding and the possibility of postoperative infection, we should stop wearing soft contact lenses for 2 weeks, hard contact lenses for 1 month, OK lenses for more than 1 month before the operation, and review the corneal topography and corrected visual acuity. 2, age At present, the age of excimer laser surgery is set at 18 years of age, there are two meanings: (1) 18 years of age is the sign of physiological adulthood, the body development is mature and tends to be static. The refractive system of the eye also tends to be static. (2) 18 years of age in the legal sense for the full capacity of the person, the decisions made for the expression of the true meaning of the individual. Therefore, when certain circumstances for the incomplete capacity to perform excimer laser surgery, must be agreed by their guardians and sign the surgical consent form. 3, refractive stability Excimer laser refractive surgery requires that the refractive power of the operated eye changes in the last 2 years ≤ 0.50 D. The vast majority of people are not sure whether their refractive power is stable or not, and the judgment of whether refractive power is stable or not must be judged by combining with the history of the disease, based on the results of the most recent optometry, comparing the result of the examination, and combining with the relationship between refractive power and age. Generally speaking, low myopia tends to be more stable than high myopia; the lower the age, the higher the degree of myopia, the less stable. 4. Visual function examination The central visual acuity examination is an important index for evaluating the preoperative visual function, and is also an important method for predicting the postoperative effect. Through visual acuity examination, we can understand the degree of refractive error on visual function, whether there is amblyopia or not, and whether other eye diseases may cause visual impairment. The examination of color vision is not a routine examination, but poor visual acuity accompanied by color vision abnormality often suggests that it is accompanied by congenital visual dysplasia or acquired eye diseases, which need further examination to exclude. Other visual function tests, such as contrast sensitivity and wavefront phase contrast, are generally used for patients with unsatisfactory corrected visual acuity to rule out possible visual function abnormalities. 5. External eye examination External eye examination should exclude acute and chronic inflammation of the eye, such as conjunctivitis and blepharitis. Eyelashes with abnormal position should be disposed of in advance if they are piercing the surface of the cornea. The condition of the cornea is the focus of the external eye examination. The pupil light and near point response is normal. The significance of checking the pupil diameter in dim light is to determine the possibility of dark environment vision impairment after surgery. The eye position has no deviation and hidden strabismus. In the author’s experience, excimer laser cannot change the strabismus, but it can improve the degree of occult strabismus, and even some intermittent strabismus disappears, especially in people with large refractive error. Perhaps it is related to the postoperative change in AC/A relationship. With the deepening of the understanding of dry eye complications after excimer laser surgery, the tear secretion function and tear film status have been paid more and more attention to.Schirmer’s test and tear film rupture time are used as routine examination to judge the tear secretion function and tear film status. 6, Intraocular Pressure Measurement As most of the people who receive excimer laser treatment are middle and high myopia, and high myopia is one of the risk factors for primary open-angle glaucoma, the incidence of primary open-angle glaucoma in highly myopic eyes is about 10%. For confirmed glaucoma or suspected glaucoma generally do not advocate the use of excimer laser corneal surgery to correct vision, due to the postoperative thinning of the cornea and curvature changes, the accuracy of intraocular pressure measurements of the currently commonly used flattening and trapping tonometers decreases, and intraocular pressure measurements are the current basis and indicators for the evaluation of the clinical effectiveness of glaucoma treatment. The error of IOP measurement is related to corneal thickness. People with high IOP and thin cornea should be highly suspected of glaucoma, and the optic papilla and visual field need to be carefully examined to exclude glaucoma. 7, corneal thickness measurement Corneal thickness measurement is one of the items that must be checked for excimer laser refractive surgery. Because the refractive correction with excimer laser will inevitably lose part of the corneal tissue at the cost, and the cornea must have a certain thickness of tissue to resist intraocular pressure, in order to maintain the normal shape and function of the cornea. Corneal topography examination Conical cornea is a contraindication to excimer laser refractive corneal surgery. Clinical type of cone cornea has obvious symptoms and signs, so the diagnosis is not difficult. Subclinical conical cornea is the focus of screening before excimer laser corneal surgery. 9, refractive index examination As the preoperative examination to determine the refractive index is the premise of successful surgical treatment, the smaller the error of the preoperative examination refractive index, the better, so as to ensure the accuracy of the expected results after surgery. 10. Fundus examination Since the fundus of highly myopic eyes is often accompanied by retinal degeneration, lacunae, and sometimes even retinal detachment and retinal hemorrhage, fundus examination is a mandatory item. Fundus examination is a mandatory item. The examination should fully dilate the pupil, when found more serious retinal degeneration area, dry hole, limited without obvious vitreous cord pulling retinal shallow detachment, can first retinal laser photocoagulation treatment, generally 2 weeks after the review of photocoagulation spot pigment appears, the crack hole is closed, after the retina is flat, still feasible excimer laser treatment. After the screening of systemic diseases and detailed ophthalmologic examination, the data collected will be comprehensively analyzed to determine: (1) whether excimer laser surgery can be performed; (2) the selection of the appropriate type of surgery.