Troubleshooting Multifocal RGPs

With this problem-solving guide in hand, you need not fear these efficacious designs.

BY EDWARD S. BENNETT, OD, MSEd & CAROL A. SCHWARTZ, OD, MBS
OCTOBER 1998

A common misperception about rigid gas permeable (RGP) multifocal designs is that they are extremely complicated and not worth the hassle. When we present these designs to potential wearers, we very often hear one of two responses: "You mean there is such a thing as a bifocal contact lens?" or "My doctor told me about them and said they don't work." Fitting bifocal RGP contact lenses should be little more complicated than fitting spherical RGPs, considering they can result in success rates of 80 percent and greater. In a very competitive environment, the referrals from enthusiastic bifocal RGP contact lens wearers can help build a practice.

We surveyed a subgroup of the Rigid Gas Permeable Lens Institute's (RGPLI) Advisory Committee for input on how to select, fit and troubleshoot RGP multifocal and bifocal contact lens designs. The committee consists of 50 contact lens practitioners who have been recognized by their CLMA member laboratory as having exceptional skills in rigid contact lens fitting. In an article published in the May 1998 issue of Contact Lens Spectrum, we presented the committee's advice on patient selection and fitting. To expand on this theme, this article will review some troubleshooting tips for these designs.

Troubleshooting Translating Designs

There are three potential challenges with translating designs: lens rotation with the blink, the lens is picked up too far superiorally and poor translation. According to our respondents, all of these challenges are easily diagnosed and managed.

Lens rotation with the blink -- A segmented translating bifocal should rotate very little after the blink. If excessive rotation occurs with a straight-ahead gaze, distance vision may be compromised by the near zone rotating intermittently in front of the pupil. Similar complications are possible with downward gaze for near viewing -- the superior distance zone could rotate into view.

The easiest management method is to simply select another base curve lens from the diagnostic set. While some Advisory Committee members recommend fitting steeper, Dr. Bennett finds fitting flatter to be beneficial. Prism ballasted lenses fit on K or flatter tend to quickly fall toward the lower lid and stay in that desirable position. If fit too steep, the tear lens tends to encourage centration of the lens, so the effects of the upper lids are greater and the lens rotates. Try changing the base curve by a minimum of 0.50D. Another method of stabilizing the lens is increasing the prism or truncation. If nasal rotation appears to be resulting from a truncated lens fitted to an upswept lower lid, change the angle of the prism base. For example, to create better alignment and less rotation, change OD from 90 degrees to 100 or 105; change OS from 90 degrees to 75 or 80.

Lens picked up too far superiorally -- A lens that is picked up too far superiorally with the blink will result in fluctuating distance vision. Typically, the lens should be positioned inferiorally, on the lower lid if truncated, and should move no more than 1.0mm with the blink.

Respondents suggested two management solutions: increase the amount of prism, usually by 0.50PD, and thin the upper edge, either by applying an anterior bevel or by tapering off the inferior portion of the lens and then thinning the superior edge. These modifications smooth the lid-lens interface, thus reducing the capability of the upper lid to control lid position.

Poor translation -- For a segmented bifocal design to be successful and provide good vision at near, the lens must push up, or translate, on downward gaze. You can evaluate this carefully through the biomicroscope while the patient is looking down. With the upper lid lifted away from the contact lens and the patient now predominantly viewing through the inferior portion of the lens, the lens should shift superiorally. If the lens is falling underneath the lower lid or is translating only intermittently, poor near vision will result.

To manage this problem, select a lens with a base curve that's flatter by at least 0.50D and determine if the increased edge clearance resulting from this change will enhance translation. If a flatter base curve is not desirable, flattening the peripheral curve radii will likewise increase edge clearance. If these procedures are unsuccessful, it is likely that the patient has a flaccid lower lid, so try changing to an aspheric multifocal design.

Troubleshooting Aspheric Multifocals

Aspheric multifocal contact lenses are relatively easy to fit. Achieving good centration is the most important fitting goal. If you cannot obtain good centration, fluctuating vision will typically result, notably at distance. The following comments are recommendations received from RGPLI Advisory Committee members for managing both inferior decentration and superior decentration.

Inferior decentration -- Aspheric multifocals should position centrally with no greater than 1.0mm of movement with the blink. If the lens decenters inferiorally or is moving excessively, the patient will be viewing through the peripheral or more plus power area of the lens, resulting in either fluctuating or blurred distance vision.

The fluorescein pattern often dictates how you may manage this problem. If desired apical clearance is not present, changing to a steeper base curve radius (with a minimum of a 0.50D change) should result in better centration. Likewise, selecting a larger diameter lens may result in less movement and greater pupil coverage. Finally, if the lens is either plus or low minus (minus power <-1.50D), the use of a minus carrier or lenticular should result in better centration.

Superior decentration -- Slight superior decentration is typically acceptable and is actually considered optimum with the Lifestyle GP lens from The Lifestyle Company. However, a lens exhibiting excessive superior decentration can result in problems including adherence, poor vision at distance and undesirable corneal topography changes.

Once again, selecting a steeper base curve radius from the diagnostic set is a good place to begin. Another management option is to ensure that the contact lens has a thin edge to minimize the effects of the upper lid. This can be accomplished by lenticulating a high minus lens, by not lenticulating low minus or plus power lenses or by applying an anterior bevel to the lens.

The Bottom Line

A new video on RGP bifocal fitting and troubleshooting is available from the RGP Lens Institute by calling 1-800-344-9060. It's apparent that fitting and troubleshooting RGP multifocal lens designs can become as routine as fitting and troubleshooting spherical designs, even though there are some differences. A trial lens overrefraction is important with these designs, so having at least one diagnostic fitting set of both an aspheric and a segmented translating design is important for achieving a successful fit.

Most of our respondents indicated that it took only three to four fits of any one lens design to feel confident in fitting bifocal or multifocal RGP lenses. Dr. Craig Bowen actually summarized RGP fitting best when he said: "No guts, no glory . . . fitting these lenses takes time and great patient management, but delivers many financial rewards as well as satisfaction and patient appreciation. One unsuccessful fit doesn't mean that all multifocals don't work!" As demonstrated in this and other articles, the fitting and troubleshooting of RGPs is very straightforward. The demand for these specialty contact lenses continues to grow. As a result, there is no reason not to satisfy your patients' needs. CLS

A special thanks to those practitioners who contributed to this article: Drs. Doug Benoit, Peter Bergenske, Sonja Biddle, Craig Bowen, John Chrisagis, Burt Dubow, Barry Eiden, Jerome Garber, Dave Hansen, Scott Kenitz, Lawrence Littlefield, Jeff Morrison, Tom Quinn, Dave Rosenbloom, Joe Shovlin, Loretta Szczotka, Roger Tabb and Ramsey Tanakasubo.

Dr. Schwartz is a contact lens consultant in Vista, Calif., and is editor of Specialty Contact Lenses: The Fitter's Guide.

Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and executive director of the RGP Lens Institute.