The severity of refractive error of the eye, mainly based on the size of the refractive error, as well as the refractive nature of the decision, as follows: 1, not serious: low degrees of refractive error will not cause eye harm. 2, serious: if the onset of the age is relatively young, and not timely corrected easily formed amblyopia. Larger degrees of refractive error can even lead to strabismus, nystagmus, as well as vitreous clouding, the corresponding lesions in the fundus, etc., seriously affect the vision is more serious. Refractive error of the eye is when the eye is completely relaxed and loosely adjusted, and the parallel light from the distance is refracted by the refractive system of the eye, it cannot form a clear image on the retina, it is called refractive error. Clinically, refractive errors are divided into three categories: myopia, hyperopia and astigmatism, the most common being myopia.