Article

PRESCRIBING FOR PRESBYOPIA

MULTIFOCAL INNOVATION

The level of innovation in contact lenses over the last few decades is overwhelming. Specifically, in the area of multifocal contact lenses, there have been innovations in material characteristics, advancements in reducing lens replacement schedules for soft lenses, and incorporation of multifocal lens optics into specialty lenses such as hybrid and scleral lenses, among many others.

When considering innovation in terms of advancements in multifocal optical lens design, there have been innovations in both mass-produced and in custom soft lenses that respect pupil size. In addition, there are increasing numbers of soft multifocal lenses that also correct astigmatism. But, when it comes to recent advancements in multifocal optical design, a few developments stand out—namely, those of extended depth of focus in soft lenses as well as the ability to offset the multifocal optics in custom soft lenses and scleral lenses.

Extended Depth of Focus Defined

The concept of extended depth of focus is a fairly new one to contact lens design and construction. The effect has been summarized as essentially a center-distance multifocal with approximately 8D to 11D of relative plus power at the pupil and approximately 20D of relative plus power at the edge of the pupil (Cooper et al, 2018).

This dramatic power shift across the optic zone is a major departure from the more traditional and more subtle lower amounts of asphericity utilized in many commercially available soft multifocal lenses. It is this significantly higher relative plus power that is created in the peripheral portion of the optic zone that is responsible for the “extended” depth of focus.

Offset Optics

Another significant innovation in multifocal contact lens design is the ability to offset the multifocal optics to better align with the visual axis. As Zheng et al described in their poster from the 2016 Global Specialty Lens Symposium, soft contact lenses frequently decenter in the temporal direction due to scleral shape changes. Additionally, our visual axis is relatively nasal to the geometric center of the cornea. Therefore, the authors surmised that these two findings work against each other in terms of the on-eye performance of not only soft multifocal lenses but also of scleral multifocal lenses.

There are now custom soft multifocal contact lenses that can be designed with the optics offset nasally to better align the patients’ visual axis, and the same can be said of scleral lenses, for which our laboratory partners are providing lens options to better serve patients and practitioners (Figure 1). CLS

Figure 1. Offset multifocal optics.

For references, please visit www.clspectrum.com/references and click on document #279.