A Clinical Comparison of Three
RGP Simultaneous Bifocals

BY TED SMILEY, O.D., SHERYL DOLLENMAYER, O.D., & GARY ANDRASKO, O.D., M.S.
MAY 1996

In this six-week study, 14 current RGP contact lens wearers in need of a presbyopic prescription were fitted with three different RGP simultaneous bifocal designs:

1. VFL-3 (Conforma Contact Lens)
2. Lifestyle Gp (The LifeStyle Co., Inc.)
3. Multifocal 19 (Contex, Inc.)

The lens power prescribed was based solely on the distance refraction (i.e., modified monovision was not used). Each patient wore each of the three bifocal types for two weeks. At the end of each two-week period, the following tests were performed:

• distance and near (Snellen) visual acuity;
• evaluation of lens fluorescein pattern;
• evaluation of lens centration (vertical and horizontal);
• evaluation of patient subjective lens comfort (using 100-point comfort scale); and
• evaluation of subjective distance and near vision (using 100-point vision scale).

Because the bifocals used in this study were simultaneous aspheric designs, the base curve-to-cornea fitting relationship resulted in a fluorescein pattern with slight central pooling to various degrees. For each design, the typical lens positioned slightly high and nasal compared to the geometrical center of the pupil. Since all of the patients were previous RGP wearers, comfort was not a significant factor in overall lens performance.

Figure 1 shows the average distance and near visual acuity measurements for each lens brand. Decimal visual acuity is plotted and the corresponding Snellen acuity is shown above each bar. On average, the Contex Multifocal 19 provided better distance vision by approximately one line compared to the other lenses (20/22 versus 20/28 and 20/27). The LifeStyle Gp lens provided slightly better near acuity (20/31 versus 20/34 and 20/24). These results are typical of any simultaneous bifocal lens in which the vision at one distance is often slightly compromised while maximizing the vision at the other viewing distance.

Snellen visual acuity doesn't always represent what the patient actually experiences in terms of vision. This is especially true of bifocal contact lenses where factors such as visual stability and quality of vision are not fully accounted for by reading a row of letters on an acuity chart.

To better evaluate the real visual experiences of our study participants, we used the following 100-point subjective vision scale:

0 = extremely blurred vision at all times

20 = moderately blurred vision most of the time

40 = mildly blurred vision most of the time with some clear vision

60 = clear vision most of the time with some visual disturbances

80 = clear vision most of the time with very minor visual problems

100 = crisp and clear vision at all times.

Figure 2 illustrates that, on average, patients preferred the distance vision of the Contex Multifocal 19 bifocal lens and the near vision of the LifeStyle Gp lens. The VFL-3 lens provided the best balance of vision at both viewing distances. In this study, the patients' subjective responses about their vision correlated well with the objective Snellen vision measurements.

When prescribing bifocal contact lenses, the overriding concern is to provide a lens type in the appropriate prescription to meet the patient's visual needs throughout the day. Simultaneous RGP bifocals are easier to fit and provide a wider range of viewing distances with less vision fluctuation than translating RGP bifocals. CLS

This study was sponsored by Contex, Inc., Sherman Oaks, Calif.

Dr. Smiley is in private practice in Columbus, Ohio; Dr. Dollenmayer is in private practice in Columbus, and is a research associate with Dr. Andrasko; Dr. Andrasko is a part-time clinical instructor at The Ohio State University College of Optometry, and a consultant to the contact lens industry.