The choice of semi-femtosecond generally depends on the degree and the shape of the cornea and the degree of regularity of the astigmatism. If the degree of myopia is not very high below 700-800 degrees, or the shape of the cornea is very regular, and the astigmatism is not very large, you can choose the ordinary form of semi-femtosecond surgery, using the femtosecond laser to create a corneal flap, followed by excimer laser corneal cutting, to complete the myopia laser correction surgery. However, if the shape of the cornea is not very regular, or if the astigmatism is large, or if the myopia has been repaired after 2 myopia surgeries, then a custom designed hemifemtosecond surgery is required. Usually, the choice of wavefront aberration-guided hemifemtosecond surgery or corneal topography-guided hemifemtosecond surgery is basically the same, but the use of corneal topography or wavefront aberration to assist in inducing the laser during the procedure is required to correct myopia and improve vision needs.