Laser corneal surgery uses a laser to cut the corneal stroma, thus changing the radius of curvature of the cornea to correct refractive errors, so there is a range of degrees of correction. The thicker the cornea, the more thickness can be cut and the greater the degree of correction. Corneal lamellar surgery generally requires that the degree of myopia should not exceed 1200 degrees, of which SMILE surgery is no more than 1000 degrees, and superficial corneal surgery requires that the degree of myopia should not exceed 800 degrees. After cutting the corneal flap, the thickness of the stromal bed in the center of the remaining cornea is generally required to be at least 250 μm, and it is recommended to be above 280 μm. A corneal bed that is left too small is prone to some corneal complications. Therefore, the exact number of degrees that each person can correct is also determined by the corneal thickness of the preoperative examination.