prescribing for presbyopia

RGP Multifocals:  Passing the "Church Test"

BY DAVID W. HANSEN, OD
May 1999

Doctor, you finally passed the "church test!" These were the words of a recent patient after I struggled to make her see with RGP multifocals. I asked her what she meant, and she responded, "I can finally see in church!"

After exhaustive investigation and casting aside my scientific background, I was able to understand this patient's statement. First, most churches have dim illumination, which makes optimum visual acuity difficult to attain, especially for presbyopes. Second, far-to-near and near-to-far focusing is customary and very important to individuals who spend time in the church environment. Third, we achieved comfort with her contact lenses under conditions of poor humidity, inadequate ventilation and allergans, which are common in most churches. What more could the patient want? I provided excellent binocular visual acuity for all distances and comfort with her contact lenses.

Success

Prescribing RGP aspheric multifocal contact lenses with the proper zones to accommodate distance and near correction under different environmental illuminations is key to the patient's perception of success. I discussed these specifics in the March 1999 issue of Contact Lens Spectrum. However, not enough emphasis has been given to the patient's desires. We keep reporting that patient adaptation is important, but maybe we're the ones who need to adapt!

Achieving Good Distance Acuity

Aspheric RGP contact lenses have received a bad rap for reducing visual acuity. This problem can be resolved with proper fitting and good design selection.

Because not all manufacturers have the same formulas for designing surfaces, it's important to know the limitations of each design. I like aspheric multifocal contact lenses because they have the capability of changing the distance center zone size to accommodate distance acuity. Patients with these lenses can usually achieve 20/20 or better under most conditions. If not, then modifications need to be made.

Achieving J1 Near Acuity

It has also been reported that aspheric multifocals are not appropriate for patients over 47 years of age with latent presbyopic needs. This is incorrect. Talk to your lab about adding plus to the front surface and changing the zone sizes to accommodate the need for near visual acuity. For years, I have been receiving +0.75D to +1.50D extra on the peripheral anterior contact lens surface in order to assist patients who are over 47 years old. I automatically prescribe this "extra add," which helps patients in most illumination situations. Since most latent presbyopic patients have intermediate range desires, modified front surface contact lenses are an excellent first choice.

Movement and Thickness

Most aspheric multifocals must center but they also move. Since the posterior surface continuously flattens from center to edge, extra edge thickness is needed to provide adequate thickness for low minus and plus power lenses.

Therefore, lenticulation is sometimes not advised because the lens will ride high, causing the patient to look through the intermediate power range rather than the center of the lens. Refractively, the patient's "expected" distance power will be less minus power than the overrefraction due to the decentration of the contact lens.

Ask your patients how they see with their multifocal contact lenses in the "real" world. If you have provided them with good acuity, then you've succeeded in passing the "church test!"

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