High astigmatism cannot be treated with excimer laser or femtosecond laser if the degree of astigmatism is more than 600 degrees in principle. High astigmatism can be treated by IOL implantation, which can treat myopia within 100-2500 degrees and astigmatism around 600 degrees. Since laser is mainly used to shape the corneal stroma, if the astigmatism is large, laser scanning will cause high order aberration and lead to poor vision, so laser astigmatism is limited to 600 degrees.