KEY TAKEAWAY POINTS
- Multifocality in IOLs is achieved through refractive or diffractive optical approaches.
- Diffractive multifocal IOLs intentionally induce diffraction so that the waves exiting the lens will have constructive interference at two or more distinct foci at different distances.
- Zonal refractive multifocal IOLs shape the waves exiting the lens from different annular regions so that they converge to two or more foci.
- The main distinction between the different optical approaches to achieve multifocality is that the out- of-focus light in the diffractive multifocal tends to be spread out uniformly over a larger area and is thereby less noticeable. The out-of-focus light in zonal refractive multifocal lenses is concentrated into rings around the objects and cannot be easily suppressed. Consequently, diffractive multifocal IOLs have replaced zonal refractive multifocal lenses as the treatment for presbyopia.
- Trifocals are an emerging technology that can utilize various diffractive optical design to create three focal points of light: distance, intermediate, and near.