Most bifocals are used to replace two pairs of bifocals that are used to see far and see near, so the position and size of the bifocals’ far-viewing area and near-viewing area should correspond to the original two pairs of glasses. If the near vision is more dominant, the subslices can be larger and higher positioned; On the other hand, if more time is spent looking far away, the sub-slices will be correspondingly smaller and lower in position. There is no one kind of design can meet the needs of different situations. It should be selected and matched according to the actual visual needs of the wearers, and sometimes different designs should be adopted to meet the visual needs of different situations with large differences.