prescribing for presbyopia
Making Sense of Frequent Replacement Soft Multifocals
BY THOMAS QUINN, OD, MS
Does anyone feel a bit overwhelmed by the broad selection of frequent replacement soft multifocals we now have at our fingertips? Take heart! Many of these designs share characteristics that,
once recognized, can help us utilize them more effectively.
One Big Similarity
Soft multifocals provide distance and near (and sometimes intermediate) optics within the pupillary space. Contrary to their gas permeable counterparts, soft lenses do not translate well on the eye during down gaze, necessitating the "simultaneous vision" approach to presbyopic correction.
Figure 1. The two most common frequent replacement soft multifocal
What's in the Middle?
One easy way to categorize soft multifocals is by what lies in their center: distance focus optics or near focus optics (Figure 1). Aspheric curves allow for a gradual transition from this central region to the periphery. Concentric, or annular, designs provide distinct, separate zones designed to allow focus at various distances.
Most frequent replacement soft multifocals utilizing a center near design are also aspheric. Examples include CIBA Vision's Focus Progressive, Sunsoft's Additions and the Unilens EMA by Unilens. This is not to say all these designs perform the same. Factors such as the speed of aspheric transition, method of fabrication and differences in material can affect performance.
Conversely, most frequent replacement soft multifocals utilizing a center distance zone are concentric in design. These designs often employ more than two distinct zones. Hence, they are referred to as concentric "multi-zone" designs.
At this time, all multi-zone designs have two things in common: central distance optics and an outer distance ring. This outer ring aids distance vision as the pupil dilates, such as with night driving. What sets the various multi-zone designs apart is what lies between the central zone and outer distance ring. Vistakon's Acuvue Bifocal has alternating near and distance zones in this region. The LifeStyle 4-Vue (LifeStyle Co.) surrounds the central distance zone with an intermediate ring followed by a near zone. The Specialty Progressive (Specialty Ultravision) utilizes a progressive intermediate-to-near optic in this zone.
An Added Twist
CooperVision's new Frequency 55 Multifocal which is derived from the UltraVue lens design by Acuity One, mixes multifocal optics with a bit of monovision philosophy. A center distance lens, which transitions through intermediate to an outer near zone, is placed on the dominant eye. A center near lens, which transitions through intermediate to distance in the periphery, is placed on the non-dominant eye. At these acuity levels, binocular summation occurs, hopefully providing clear vision at all distances under binocular conditions.
No single design works for all patients. I suggest having at least one design from each of the above categories on hand to improve the odds that you'll be able to provide what both you and the patient want: clear vision.
Dr. Quinn is in group practice in Athens, Ohio, and has served as a faculty member at The Ohio State University College of
Contact Lens Spectrum, Issue: March 2002