Bifocal glasses are mainly suitable for the elderly to see far and near. After a person reaches old age, due to physiological reasons, his vision deteriorates and his eyes are presbyopic. Bifocal glasses can help the elderly see far and near. Let’s take a look at the bifocal glasses. Bifocal glasses are also called bifocal glasses, and the optical effect of the main lens is the same. Bifocal glasses mainly include tangible bifocals and invisible bifocals. Bifocal glasses are made by bonding or fusing two refractive index lenses. One type of tangible bifocals is by pasting a small piece of different power under the large lens, which is easy to fall off. The other is a first-line bifocal lens, that is, two diopters are ground on the blank, and a horizontal line interface can be seen in the middle. Since the sub-lens is attached to the main lens, the phenomenon of image jumping and image defect will also occur. Invisible bifocal glasses integrate the small lens into the large lens. There is no obvious boundary between the large and small lenses, which does not affect the appearance. This kind of bifocal lens will have image jump and image defect, which is inevitable. At present, the shapes of the sub-lens of bifocal glasses mainly include dome bifocals, flat top bifocals and first-line bifocals. The first-line dual-light near-use zone is relatively large, so it is more suitable for people who use more eyes at close range. The dome double light and flat top double light are suitable for people with more distant use areas. From the point of view of the production process, there are three types of fusion double light, glued double light and overall double light. Gluing dual-lens is to paste two polished lenses together, fusion dual-lens is to fuse the lenses together, and the dual-lens of the polished power; the overall double-lens is the main and sub-lens of the same material and one The overall double light. The lenses of bifocal glasses need to include distance diopter, near diopter or add light, far pupil distance, near pupil distance, sub-lens apex height, frame and lens type. The measurement of bifocal glasses includes the determination of the distance pupil distance, the near pupil distance and the height of the apex of the sub-lens. The pupil distance is consistent with the measurement method of general single-lens glasses.