Investigating A New Multifocal Contact Lens Design

BY JEROME LIEBLEIN, O.D.

This clinical investigation sheds light on the performance nuances of a multifocal contact lens series that gives practitioners a variety of fitting options.

A new presbyope emerges every 7.5 seconds. Monovision and eyeglasses can't satisfy all the needs of this vast population -- more options are needed. Fortunately, the correction options available today enable us to manage the presbyope better than ever before.

PRODUCT PROFILE

As an investigator for various contact lens companies, I have the advantage of being able to evaluate new products as they become available. One such product is the ABCON Vision soft contact lens series, manufactured by Nissel, Ltd. in England and distributed in the United States by World Optics, Inc., Agura, Calif. The ABCON design is also now available in an RGP contact lens series, and clinical trials are underway to see how the RGPs will perform relative to their hydrogel counterparts.

The ABCON series includes two lenses: ABCON D -- a distance lens with an increased depth of focus equivalent to an add of up to +0.75D (+1.50D with a pair); and ABCON N -- a simultaneous center-near multifocal which gives +2.00D of add centrally and progressively descends to distance power within the pupil area (Fig. 1 ). Both lenses are designed with an aspheric anterior surface that controls and reduces spherical aberration, providing a smaller blur circle (Fig. 2) and masking up to 1.50D of astigmatism, according to the manufacturer. For success, front aspheric designs necessitate following the recommended fitting guides.

The design of the ABCON lenses gives the practitioner the ability to fit them as a single-vision system, a combination system or a full multifocal. I've found the lens design provides sharp, clear visual acuity, even at night. The lenses are comfortable for the patient to wear, they create fewer halo or starburst effects, and they're less likely to induce the feeling of imbalance or dizziness commonly associated with other bifocal contact lenses or monovision. ABCON contact lenses also return the depth perception that is lost when fitting spherical monovision.

The key to each of the three fitting choices furnished by the ABCON design series is to first determine the eye that will accept the most plus (near eye). This step is most important because each fitting system depends on maintaining the natural dominance for near and far. The techniques that the manufacturer recommends for determining proper lens power are binocular systems and require that both eyes be open.

STUDY RESULTS

I randomly selected 15 patients with various refractive conditions who had previously worn ABCON lenses in one of four fitting variations (Tables 1 & 2). The patients consisted of six men and nine women ranging in age from 35 to 62. Pupil sizes ranged from about 3.0mm to 8.0mm. The average number of visits to completion was 3.7, including the initial examination.

Twelve of the 15 patients were successful. Of the three patients who failed, all had pupil sizes of about 3.0mm or smaller. While all three achieved desired near visual acuity, desired distance visual acuity was unobtainable without a decrease in the near visual acuity. This can be explained by the design of the ABCON N lens. The distance prescription of this lens is positioned 1.5mm out from the center of the lens, so the small pupil size wouldn't allow light rays to pass through the distance prescription focal area. This prevented the patients from achieving desired distance acuity unless we changed the prescription of the lens to bring the distance focal point to less than 3.0mm (i.e., using a lens with more minus power). However, more minus power decreased the desired near acuity for all three patients.

THE SECRET TO MULTIFOCAL SUCCESS

As with any progressive soft lens, the secret to success is having a trial set or, if available, a large fitting set. Even 0.25D can make a one- or two-line difference which could be the deciding point between success and failure. Using a large fitting set was a contributing factor to my high success rate with this lens because I was able to change the power and refine lenses on the spot.

As practitioners, we should explore all possibilities of presbyopic correction. In my experience of analyzing various contact lenses, I have tested dozens of multifocal contact lenses, gas permeable as well as soft. I find that the products available at this time can satisfy the needs of our presbyopic patients without sacrificing depth perception. CLS