[The advantages and disadvantages of bifocal lenses].

The bifocal glasses present three main disadvantages: the jump of the image when the visual axis passes from the far vision glass to the reading segment, the prismatic effect on the near vision point that entails an apparent displacement of the fixed object as well as a degradation of the quality of its image, and the absence of intermediate vision in total presbyopia. Bifocals however keep their indications, even after the availability of the progressive glasses, by people accustomed with this kind of correction, and by others who are not supporting deformations in the lateral vision of the progressive glasses. Suggestions are made for choosing the model of bifocal which is the most appropriate in function of the different situations.