The main components of the preoperative evaluation for excimer laser keratomileusis include four main areas, namely assessment of expectations, medical history assessment, eye examination and informed consent. Keratomileusis has been experienced in China for 20 years so far and has become by far the most reliable and effective surgical procedure for freeing myopic people from wearing glasses. With the development of surgery, including the understanding of surgery and the updating of equipment, certain previous absolute contraindications have become relative contraindications, but patients with cone keratoconus, cyclopia, and active systemic immune disease are still absolute contraindications to surgery. The relative contraindications to keratoconus surgery are described here. 1, dry eye Corneal refractive surgery, especially LASIK, the incidence of postoperative dry eye up to 50% or more, some investigations up to 90%, the duration of long, and the damage to the functional units of the tear gland. Although postoperative dry eye can be relieved with time, it can cause long-lasting eye discomfort, fluctuating vision, vision loss, and some dry eye patients can lose more than two lines of vision. Possible factors that lead to preoperative dry eye include, sandy air conditioning environment, female population, corneal contact lens wear, chronic inflammation of the eye, long-term use of eye medications containing preservatives, computers, and various eye surgeries are all factors that cause dry eye, and many patients It is because of dry eyes that they cannot tolerate contact lenses that they request surgery. In the management of preoperative dry eye patients, our experience is that surgery is contraindicated in patients with systemic dryness and can be performed at the discretion of the patient after treatment of simple dry eye. Treatment includes treatment of ocular surface inflammation, etc., tear replacement therapy and tear embolization, etc. 2, herpes simplex virus keratitis Corneal lamellar incision and excimer laser irradiation may activate the virus, and postoperative glucocorticoid use increases the likelihood of recurrence. For the management of these patients, our principle is that surgery is not recommended if there is significant corneal perception reduction, neovascularization affecting surgery or recent herpetic disease. LASIK can be done for patients with stable corneal conditions, good perception recovery, little neovascularization, and no impact on surgery and postoperative vision, and prophylactic antiviral medication before and after surgery can help. 3, superficial keratopathy This keratopathy may lead to postoperative corneal epithelial exfoliation, corneal flap edema, poor corneal flap formation, treatment can be antibiotic eye solution and low concentration of hormone therapy, remission after surgery, and still need to continue to pay attention after surgery. 4. Immune-related ocular diseases such as sclerositis, vesicular conjunctivitis, etc., also require preoperative treatment (glucocorticoids) because they may cause postoperative corneal flap lysis. 5. Chronic ocular surface inflammation, blepharitis, and blepharitis. Not only may they lead to postoperative infection, but they are also associated with persistent unrelieved postoperative dry eye and also need to be treated aggressively. 6, corneal epithelial basement membrane dystrophy performance corneal epithelial map-like changes, in making LASIK surgery, the epithelium may move with the lamellar knife, causing damage, if myopia is not too high, you can choose PRK, both to correct myopia, but also has a therapeutic effect. 7, thin cornea We are most concerned about the possibility of postoperative corneal expansion and cone cornea. The current domestic and international recommendations are that the corneal thickness after LASIK is not less than 400 μm, the corneal bed thickness is more than 280 μm, and the reserved thickness is not less than half of the original corneal thickness. With the update of surgical methods, for thin corneas, you can choose superficial surgery, superficial lamellar surgery, or refractive lens surgery (ICL). 8, corneal topography abnormalities If conical cornea is diagnosed, keratoconus surgery is contraindicated, suspected conical cornea, follow up for two years, and then consider surgery after exclusion. Clear limbal keratoconus contraindicates keratomileusis, preoperative corneal curvature too high (>48D) or too low (<40d) due to the increased risk of doing corneal flap, can consider superficial surgery or femtosecond laser flap making, if the expected postoperative corneal curvature is too high (>50D) or too low (<34d), it will greatly affect the visual quality, theoretically not an indication for keratomileusis, we will generally choose intraocular lens implantation surgery. 9, high IOP, glaucoma From the prevalence, 9-28% of myopic patients can be accompanied by primary open-angle glaucoma; transient negative pressure attraction may potentially aggravate optic nerve damage; postoperative glucocorticoid use can lead to elevated IOP in hormone-sensitive individuals; postoperative pseudo-low IOP values affect the follow-up judgment of glaucoma; precise postoperative assessment of IOP remains difficult. Therefore, in patients with high IOP, all exclusion tests for glaucoma should be performed first. For progressive glaucoma, surgery is contraindicated, whether it is keratomileusis or intraocular lens surgery, and for hyperopia, it is controversial whether to operate, because a portion of hyperopia will have optic nerve damage and visual field loss, and surgery is clearly detrimental to them. Therefore, it is believed that hyperopia and glaucoma are not absolute contraindications to refractive surgery, but are at least relative contraindications. 10.High myopia with fundus disease Negative pressure attraction, laser acoustic wave, etc. may have certain effects on the retina. Our principle is to perform retinal photocoagulation on retinal fissures or degenerative areas with traction, and choose the timing of surgery according to the local pigmentation, usually about 2-4 weeks, and avoid negative pressure attraction as much as possible in the operation. 11.Adult refractive error with monocular amblyopia For mild to moderate amblyopia with corrected visual acuity above 0.5 - surgery can be considered, but it is explained to the patient that surgery does not improve corrected visual acuity, and that surgery for severe amblyopia with corrected visual acuity below 0.1 is not meaningful, and that any refractive surgery in the contralateral eye should be contraindicated due to the risk of surgery.