Myopia of 400 degrees belongs to moderate myopia, so vision will be significantly affected when looking at a distance, especially in the form of reduced clarity, while relatively clearer when looking at a nearer distance. Patients may look at objects several meters away and see that the boundaries become blurred, contrast sensitivity decreases, it is not easy to distinguish between similar colors, and they can only see the general outline of things as well as bright and dark surfaces. Myopia is a disease caused by problems in the refractive system of the eye. When parallel light rays are refracted by the refractive system of the eye, they cannot be clearly imaged on the retina, but are focused in front of the retina, so it is necessary to wear corrective lenses, and myopia is often corrected with concave lenses to correct the vision, so as to make the object image present a clear image.