Fitting a New Silicone Hydrogel Multifocal Design
BY CRAIG W. NORMAN, FCLSA
In my February 2006 column "Silicone Hydrogel Lenses and the Presbyope," I provided a general overview of silicone hydrogel lenses for presbyopes primarily describing the benefits of using high-Dk materials for this patient group. Since then Bausch & Lomb has introduced the first silicone hydrogel multifocal in this category, the PureVision Multi-Focal.
The PureVision Multi-Focal lens has some similarities to other soft multifocals in that it employs a center-near correction. The aspheric anterior surface creates a power gradient across the optic zone with more plus power centrally than in the peripheral area, thus creating the multifocal effect. The design is available in two add powers low and high (Figure 1). The spherical back-surface design provides a traditional soft lens fitting relationship.
PureVision Multi-Focal is similar in design to the SofLens Multi-Focal except that it's currently available only in one base curve rather than two, while having the same power availability.
The aspheric front surface design incorporates varying shape factors for each distance power as an applied means of controlling the spherical aberration generated by different optical powers.
Figure 1. Optical design of PureVision Multi-Focal.
Clinically, we've found fitting the PureVision Multi-Focal quite straightforward. The single base curve fits most patients with good centration and movement.
Diagnostic fitting is helpful, and when doing so we correct the full distance correction, taking into consideration the spherical equivalent for patients who have less than 1.00D of cylinder.
For early presbyopes who have spectacle add power needs of +1.50D or less, we initially select the low add for each eye. For patients who have adds from +1.75D to +2.25D, we begin with the low add for the dominant distance eye and the high add for the fellow eye. For +2.50D adds we usually choose the high add OU.
In addition to new wearers, many patients whom we've fit with this lens are long-term hydrogel wearers who may be experiencing limbal redness and neovascularization from corneal oxygen deficiency. The improved corneal oxygenation of this lens decreases these signs.
When switching from hydrogel designs, some of our patients describe a little awareness for the first few days, similar to what we've seen with other silicone hydrogels. Most wearers become more comfortable with this material the longer they wear it.
Silicone hydrogel multifocals are a welcome addition to the offerings for our presbyopic patients. We've found that the PureVision Multi-Focal provides a level of wearing convenience that many presbyopes are seeking good vision at distance and near, plus the possibility to safely nap or sleep in their lenses.
As the use of silicone hydrogel multifocals becomes more common, presbyopic patient success should continue to increase significantly.
Craig Norman is director of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He is a fellow of the Contact Lens Society of America and is an advisor to the GP Lens Institute. He is also a consultant to B&L.