Introduction

When a person’s eye adjustment is weakened due to age, he/she needs to correct his/her vision separately for the far and near vision. At this time, he/she often needs to wear two pairs of glasses separately, which is very inconvenient. Therefore, it is necessary to grind two different refractive powers on the same lens to become lenses in two areas. Such lenses are called bifocal lenses or bifocal glasses.

The main raw material of glass lens is optical glass. The transmittance and mechanical and chemical properties of glass lens are relatively good, with constant refractive index and stable physical and chemical properties.

This kind of dual-light mirror has a large proximity area. It is a kind of non-image hopping dual-light mirror, which can be made of glass or resin. In fact, E-type bifocal mirror can be considered as the negative degree of additional far-sight on the proximity mirror. The thickness of the upper half edge of the lens is relatively large, so the thickness of the upper and lower edges of the lens can be the same through the prism thinning method. The size of the vertical prism used depends on the near addition, which is yA/40, where y is the distance from the dividing line to the top of the sheet, and A is the reading addition. Since the near attachment of the two eyes is usually equal, the thinning amount of the binocular prism is also the same. After the prism is thinned, the refractive film shall be added or subtracted to eliminate the internal refraction.