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.Binocular lenses or bifocal lenses are lenses that contain two correction areas at the same time and are mainly used for presbyopia correction. The area where the binocular lens corrects the far vision is called the far vision, and the area where the near vision is corrected is called the near vision and the reading area. Generally, the far field is large, so it is also called the main field, while the near field is small, so it is called the sub-field.