Refractive error refers to the condition where, without accommodation, parallel light rays passing through the refractive media of the eye do not form a clear image on the retina, but rather form an image in front of or behind the retina. This includes hyperopia (farsightedness), myopia (nearsightedness), and astigmatism. For myopia treatment, light to moderate myopia can be corrected with appropriate concave lenses; in cases of hyperopia, if vision is normal and there are no subjective symptoms, no treatment is needed. However, if there are symptoms of visual fatigue, appropriate convex lenses should be used for correction; astigmatism requires the correction with cylindrical lenses.