Contact Lens Design & Materials
Advancing Soft Multifocal Contact Lens Design
BY RONALD K. WATANABE, OD, FAAO
Many columns have been written about multifocal contact lens designs, for obvious reasons. Not only is there a vast demand for soft presbyopic contact lens options, but also no designs have ever been able to replicate the natural focusing of the pre-presbyopic eye (nor do I think that any ever will). But lens design technology marches forward, and new options are introduced each year. Today’s soft multifocal options include aspheric, concentric, multi-zone, alternating zone, and segmented designs. There are daily disposable and high-Dk frequent replacement options.
Custom designs offer even more versatility. Specialty labs can make lenses with virtually any curvature, diameter, and power. Each lab may have more than one design available. They can make lenses with center-distance or center-near zones. A few custom labs have the ability to adjust the diameter of the center power zone. This gives a practitioner the ability to customize the power zones to different pupil sizes, and it also provides more flexibility in fine-tuning vision at distance and near based on a patient’s visual response.
New to Market
A new entry into the soft multifocal arena is the SpecialEyes 54 Aspheric Multifocal (SpecialEyes, LLC). It is a contrasting alternative to the concentric bifocal design that the company has offered for several years. It is fit in the same way as SpecialEyes’ other custom lenses, using the sagittal depth of the cornea as calculated from corneal curvature and diameter to select the most appropriate base curve and diameter. Centration of the lens is important, so having a wide range of fitting parameters is critical to success.
Optically, the lens has a near center surrounded by an aspheric intermediate zone and a peripheral distance zone (Figure 1) that appears similar to other designs currently available from other manufacturers. The SpecialEyes design is also available in a center-distance version, though the near center is the default option. The center zone has a standard diameter of 2.0mm, and the peripheral zone (transition between intermediate and peripheral zones) has a standard diameter of 4.0mm.
Figure 1. SpecialEyes 54 Aspheric Multifocal lens design.
But, the advantage of this design is that the two zone diameters are also independently adjustable in 0.1mm increments. The near-center zone can be made larger to improve near vision or smaller to improve distance and intermediate vision. The peripheral zone also can be made larger or smaller to affect distance and intermediate vision. Or, they can both be changed together to achieve the desired improvement in vision.
And, remaining consistent with its other lens offerings, the power and base curve ranges are extensive, including toric powers up to –8.00D and add powers up to +4.00D.
This new design gives a practitioner more power to fine-tune a patient’s vision depending on lens performance and visual needs. It is yet another advancement to help practitioners in the ongoing challenge of providing our presbyopic patients with satisfactory vision. 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, Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at email@example.com.