The definition of myopia is as follows: If the degree of myopia is greater than 50 degrees after optometry, it can be called myopia. Between 50 degrees of nearsightedness and 50 degrees of farsightedness is called orthopia. Greater than 50 degrees of farsightedness is called hyperopia. Myopia between 50 and 300 degrees is called low myopia; between 300 and 600 degrees is moderate myopia; 600 degrees or more is high myopia. Low myopia has a relatively small effect on vision, with about 0.1 to 0.2 vision at 300 degrees. However, medium and high myopia have a very big impact on vision, and the general vision is around 0.1, which very much affects the clarity of daily vision and the safety of daily life. Therefore, medium and high myopia, even in adults, is recommended to wear myopic glasses to ensure daily safety as well as clear vision.