Based on clinical experience, lenses with a refractive index of 1.67 are usually sufficient for patients with 650 degrees of myopia, or 1.74 if the budget is sufficient. The advantage of 1.67 refractive index lenses is that they are inexpensive for daily use; the advantage of 1.74 refractive index lenses is that they are thinner and lighter. 1.67 and 1.74 are both refractive indices of lenses, and the larger the number, the higher the refractive index, the thinner the center of the final lens and the lighter the lens. Since the glasses themselves are not heavy, the difference in weight and thickness between the two types of lenses is basically unnoticeable to the human body. When choosing lenses, patients should consider not only the refractive index of the lenses, but also the degree of their myopia and their budget for prescription lenses. If you care about the overall weight of the glasses, you can also choose lighter alloy frames. The user should go to a regular hospital and have a detailed specialist examination before optometry, especially for minors and first-time prescriptions, to exclude other diseases and to distinguish between true myopia and pseudomyopia, and if necessary, to conduct multiple examinations to avoid errors.