prescribing for presbyopia

Selecting the Preferred Presbyopic Contact Lens Option

BY DAVID W. HANSEN, OD
November 1999

For the first 40 or more years of their lives, most baby boomers have grown accustomed to binocular vision and good visual acuity. It seems only fair that we should continue to provide them with these same critical abilities as they become presbyopic.

Soft lens manufacturers have recently introduced great multifocal contact lens options to assist our presbyopic patients. The key to making the correct selection between a soft lens and an RGP lens is understanding the basic concept of each design.

Basic Design Concepts

The concept that an RGP moves and a soft lens is relatively stationary seems rather simple, but is often overlooked. This is an important fitting principle that has to be taken into consideration when moving from a single vision modality to a multifocal design.

It's also important to understand that translation occurs in all RGP lenses, including aspheric and translating designs, and that clarity of vision for soft multifocal lenses is derived from "zone sizes." By the nature of these two materials, one or both may be successful. But remember, some patients may be better suited for distance center adds and other patients may be better suited for peripheral presbyopic correction, in which case, careful measurement of the pupils is important.

Since translating soft contact lenses are no longer manufactured, aspheric designs are available in both posterior and anterior surface designs. Typically, back surface aspherics have a limited reading power but may offer clearer distance vision. Front aspheric multifocals feature a higher reading power but may compromise acuity or contrast sensitivity for distance.

Concentric designs with the distance zone in the center may yield better distance vision but may limit the nearpoint acuity. Concentric or annular designs with the near zone in the center may also allow for better reading. Before selecting either of these designs, determine the patient's true needs. If the patient has critical near tasks, select a larger near zone to accommodate his working distance. The opposite is true for patients with distance demands. As with aspheric RGP bifocals, centration over the pupillary aperture is critical.

Don't Give Up

Before you give up on a true soft multifocal design, realize that manufacturers offer yet another option, a modified multifocal. Acuity One, L.L.C. provides the UltraVue bifocal system which uses a concentric spherical design. The dominant eye is fit with the distance power located in the center for various sizes surrounded by a near zone in the center, surrounded by the distance. The Lifestyle Company uses a similar design for their MV2 lens (Fig. 1). The dominant eye is fit with a distance centered lens which has a surrounding intermediate zone, and the nondominant eye utilizes the near vision in the center with an intermediate in the peripheral portion of the lens.

Millions of dollars have been invested in the research and development of soft lens options for presbyopic patients. Try using these designs as an adjunct to your RGP multifocal options. You just might like them.

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