contact lens design and materials
Design Characteristics of Two New Soft Multifocals
BY RONALD K. WATANABE, OD, FAAO
In the never-ending struggle to fit presbyopes with soft lenses that deliver good vision at all distances, two new multifocal soft contact lenses are welcome additions: Acuvue Oasys for Presbyopia (Vistakon) and Air Optix Aqua Multifocal (Ciba Vision).
Acuvue Oasys for Presbyopia
Vistakon's approach in designing Acuvue Oasys for Presbyopia was to combine the positive design aspects of aspheric and ring designs into a new aspheric zonal design. Ring designs of alternating distance and near rings are less dependent on pupil size but have issues with ghosting, glare, and halos. Aspheric designs deliver more balanced vision across all distances but are more pupil size dependent. Acuvue Oasys for Presbyopia is a synergistic combination of these two general design concepts, resulting in an “aspheric zonal” design consisting of a center-distance aspheric zone surrounded by alternating aspheric zones on the front surface of the lens. This new Stereo Precision Technology design is intended to provide balanced vision at all distances across varying illumination levels with minimal ghosting, glare, and halos.
Acuvue Oasys for Presbyopia also features an aspheric back surface to help maintain lens centration, preserving the front-surface optics. The lens is also designed to leverage the eye's natural depth of focus.
Finally, the senofilcon A material is an excellent choice for presbyopic patients who may benefit from the high Dk/t (147) and the Hydraclear Plus technology, which is designed to provide comfortable wear for patients throughout the day. Acuvue Oasys for Presbyopia is now available in distance powers from +6.00D to −9.00D in three add powers (low, mid, and high), a base curve of 8.4mm, and a diameter of 14.3mm.
Air Optix Aqua Multifocal
Ciba completely redesigned the Air Optix Aqua Multifocal. Like its predecessor Focus Progressives, the Air Optix Aqua Multifocal has a center-near aspheric design. However, the similarities end there. While the Focus Progressives' steep power profile went from near to distance power within a very small area, the Air Optix Aqua Multifocal's “Precision Profile Design” has a much smoother power transition from center to edge, which creates a more evenly controlled rate of change. This optical design extends the wearer's depth of focus more cleanly to deliver clearer vision at distance and near while minimizing ghosting and other optical artifacts. The power gradient is also designed to be uniform across the wide power range, so it provides the same effective add power at −3.00D as at +3.00D, which was not always true with previous center-near designs. The Air Optix Aqua Multifocal is also available in three different add profiles (Lo, Med, and Hi), unlike the “one-size-fits-all” Focus Progressives. The lotrafilcon B material is also an excellent choice for presbyopes, with a high Dk/t (138 at −3.00D) and the Aqua Moisture System. Air Optix Aqua Multifocal is now available in distance powers from +6.00D to −10.00D in 0.25D steps, a base curve of 8.6mm, and a 14.2mm diameter.
Neither of these new lenses are simply silicone hydrogel versions of their previous lenses. They are optically more sophisticated and refined, and they use the latest in material technology. Though they still have some of the limitations of simultaneous vision designs, they hold promise for better visual performance and more comfortable wear time. CLS
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry's Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass.