When refer to how to choose the lens. we will talk about the refractive index, coefficient of wear resistance, spherical selection, Abbe number, anti-fouling ability, brand selection, and functional choice. 1.Refractive index The refractive index of the lens is determined by the material of lens. In the case of the same thickness of the center, the lens of the same degree and the same material, a thinner edge of the lens has a higher refractive index; when the brand is the same, the refractive index means the different usage of the material, and the price of the lens can also be judged. The higher the refractive index, the higher the price. Refractive index selection reference: (For reference only, do not completely follow it) 1.56: 0 — 400° (-4.00D) 1.60: 300° (-3.00D) — 600° (-6.00D) 1.67: 400° (-4.00D) — 800° (-8.00D) 1.74: 800° (-8.00D) or above2. Wear r...