Normal refraction is considered orthopia, with a normal range of 25° or less. In terms of myopia the standard for mild myopia is between 25° and 300°, while the standard for mild hyperopia is 0° and 300°. When the eye is adjusted at rest and external parallel light rays pass through the eye’s refractive system and are able to focus exactly in the macular sulcus of the retina, this refractive state is called orthophoria. Because the eye may be regulated, myopia of 25° or less is normal. When the regulation of the eye is relaxed, parallel light rays cannot be focused in the macular sulcus of the retina, which will not produce a clear image is called refractive error. Therefore, if you find that your vision is not normal, you need to go to the hospital for an optometric examination, and if you are diagnosed with farsightedness, myopia, astigmatism, etc., it will cause the prescription of glasses or surgical correction.