A, according to the material points
Common lens materials include ordinary resin sheet, PC resin sheet, glass lens and crystal lens. Ordinary resin sheets account for most of the market, with good transparency, firmness and low price. PC cosmic film is stronger, lighter, UV-proof, more expensive and better in quality than resin. Glass sheets are more wear-resistant and have higher refractive index, but they are too heavy and fragile; Crystal tablets are too expensive and have poor ability to prevent harmful light, so they are not suitable for daily use.
Second, according to the design
Divided into spherical lens and aspherical lens. Spherical lenses will distort objects, while aspherical lenses will be clearer, more realistic and lighter. Basically, you will choose aspherical lenses when you buy them. Of course, there is a market for spherical lenses, and some people buy them.
Third, according to the processing points
Surface treatment without film; Adding dura mater can protect lenses and enhance resistance and wear resistance; Anti-reflection film can improve the visual effect, but also has a certain protective effect; Anti-fouling film, so that the lens is not easy to get dirty, oil stains, water stains and so on. What kind of plastic film to cover, according to your own needs to choose.
Fourth, by color.
Can be divided into white and colorless lenses; Dyed tablets, dyed with chemicals; Color-changing sheet, which is decomposed into silver and halogen by adding silver halide under strong light stimulation, so that the color of the lens becomes darker, and then combined into silver halide after the illumination becomes weaker, and the color becomes lighter; The polarizer only allows light to pass in a certain direction, so it can filter out some stray light. Myopia lenses are mostly white with good light transmission, and there are also yellow anti-blue lenses.
Five, according to the thickness
There are ordinary and ultra-thin lens thicknesses. Here we introduce a concept called refractive index. The higher the refractive index, the thinner the lens and the higher the price. But you can't blindly want a high refractive index. You should choose a reasonable refractive index according to the degree of myopia. You can refer to:
For myopia or flat light below 1 and 100 degrees, it is recommended to choose lenses with refractive index of 1.50;
2, 100~300 degrees myopia, it is recommended to choose 1.56 refractive index lens;
3, 300~600 degrees myopia, it is recommended to choose lenses with refractive index of 1.60;
4, 600~800 degrees myopia, it is recommended to choose lenses with refractive index of 1.67;
For myopia above 5.800 degrees, it is recommended to choose lenses with refractive index of 1.74.
The above is for reference only, subject to the actual situation. Lens thickness is also related to myopia, lens material, frame size and other factors, the thinner the better. The refractive index 1.74 and above are basically imported from abroad, and the domestic technology is not mature.
To sum up:
In the final analysis, myopia lenses should be comfortable and suitable for themselves. If the requirements for the lens are very high, it can be configured as follows: the material is PC, and the aspheric design is adopted. According to the actual situation, the film is added, and the functions of preventing blue light and fatigue are added. And the refractive index is selected to be high within a suitable range.