prescribing for presbyopia

What's New with RGP Bifocals

DAVID W. HANSEN, OD
JANUARY 1998

As Benjamin Franklin said in 1734, "Don't think to hunt two hares with one dog." If you're stuck in a rut when prescribing contact lenses for presbyopia, it's time to seek new alternatives with RGP bifocals. Many skeptics of RGP bifocals say there are no new designs. They may be right, but the enhancements made by many of the manufacturers gives us new opportunities for success.

Translating Designs

Crescent bifocals have been around for many years, but this one-piece construction, thin, no-jump (monocentric) design is available in new RGP materials today. Metro Optics suggests using a 60Dk material. Solutions by Xcel Contacts recommends using a Dk of 30 or 60 because of the thinner design. Menicon's crescent lens is made in SF-P material which has a Dk of 100.

The crescent design has received acclaim because it provides a wide field of view for distance and near. The no-jump design helps patients translate from distance to near and back. The lenses are traditionally made without truncation and give the patient excellent comfort even though the design is prism-ballasted.

Simultaneous Designs

Most of the laboratories manufacturing simultaneous lenses have a new challenge. More presbyopes are advancing into their late 40s and 50s, needing greater add power. Today's designs now have a wider range of focus, which must be included into the same diameter lens without disrupting translation from far to near.

To incorporate more ranges of focus, some of the laboratories have added plus power to the front surface and also changed the e-value of the posterior aspheric surface. Others have designed lenses with an aspheric front surface and an aspheric back surface, similar to the LifeStyle design. This design also enhances the fit on the aspheric cornea.

Some contact lens laboratories cater to the emerging presbyope. Fused Kontacs' No Line uses a back-aspheric design intended to produce at least +2.25D of near add. Similar to a single-vision lens, the fitting philosophy is to match corneal curvature.

Polymer Technology recently introduced the Boston MultiVision RGP multifocal, a posterior surface multi-aspheric design made in Boston ES material. The lens functions best with an alignment fit in the central portion of the cornea. Its elliptical center provides a low eccentricity for distance, and its greater eccentricity, hyperbolic reading area is positioned peripherally. The transition zone between the two is the "fillet" curve.

Keep in mind that the products mentioned here are the newest designs, but there are many other options available. Be sure to contact your RGP lab to learn about new products. CLS

Today's RGP Bifocal Designs Offer:

• Reduced lens weight
• Better comfort
• Sharper acuity over a wider performance range
• Greater near adds to meet the needs of the aging population.

Manufacturer Contributions Include:

• New lathing technology
• Better reproducibility
• New gas permeable materials which offer better oxygen and comfort for the patient, including Boston ES from Polymer and HDS from Paragon .
• New care products to work in synergy with lenses
• Enhancement of previous bifocal designs for ease of patient adjustment.

Dr. Hansen, a diplomate and fellow of the AAO, is in private practice in Des Moines, Iowa.