prescribing for
presbyopia
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.
Lens Construction
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.
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Figure
1. Optical design of PureVision Multi-Focal.
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Fitting Process
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.
Patient Uses
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.
Contact Lens Spectrum, Issue: September 2006