Refractive error is the medical term for the failure of the eye to form a clear image on the retina after parallel light rays have passed through the refractive action of the eye without adjustment (completely relaxed state) for various reasons, and the focus of the object is not concentrated at one point or the point of concentration falls in front or behind the retina. Refractive errors include nearsightedness, farsightedness and astigmatism. Myopia refers to the eye in the state of adjustment and rest, from 5 meters of equal light through the refraction of the eye, the focus falls in front of the retina, can not form a clear image, this refractive state of the eye is called myopia. Myopia can be divided into three grades according to the degree, mild myopia, moderate myopia and high myopia. Nearsighted eyes can see small targets without adjustment or with less adjustment when working at close range, which is more convenient than ortho-optic eyes. However, in highly myopic eyes, the target distance is very close when working, and both eyes collect too much inward, which will cause excessive use of the internal rectus muscle and visual fatigue symptoms. Farsightedness is the state of the eye in the regulation of static, from 5 meters of equal light after the refraction of the eye, the focus falls after the retina, can not form a clear image, this refractive state of the eye is called farsightedness. The visual acuity of a hyperopic eye is determined by the level of its hyperopic refractive power and the strength of its regulation. Mild hyperopia, which can be overcome with a small amount of regulation, can be normal in both distance and near vision, and is generally asymptomatic, is called occult hyperopia. The remaining part that cannot be completely compensated by regulation is called dominant hyperopia. Farsighted eyes are prone to visual fatigue symptoms due to long-term regulatory tension. Astigmatism is a refractive error of the eye that is related to the curvature of the cornea. Some people have a curved cornea at one angle and a flattened cornea at another angle, which causes light to not focus effectively at one point after refraction, resulting in a false image and a deviated sense of spatial position of objects. Patients with low astigmatism do not feel obvious, while those with higher astigmatism may have reduced vision, unclear vision at distance and near, seemingly double vision, and often have symptoms of visual fatigue.