prescribing for presbyopia
Cut Down on Fitting and Chair Time with a New GP
BY CRAIG W. NORMAN, FCLSA
When fitting presbyopic patients with contact lenses, we have two primary goals:
1. To fit patients successfully, providing functional vision for all of their daily tasks with a lens that's comfortable and physiologically compatible with the eye.
2. To achieve these results in a timely fashion
Most presbyopes today lead busy lives -- they juggle family and work responsibilities and aren't interested in taking part in a long, drawn-out contact lens fitting process. Thus, it's important to reduce the number of patient visits as well as your chair time.
Presbyopic contact lens manufacturers are diligent in creating products and fitting systems that allow us to achieve these goals. They continue to develop designs that use novel approaches to improve the technical characteristics of their innovations. Now some are making great strides in simplifying the fitting process.
Figure 1. Typical fluorescein pattern of the LifeStyle Marquis GP Design: noticeable clearance centrally, mid-peripheral alignment, then a return to peripheral
Checking Out a New Design
Recently, I had the opportunity to evaluate a new lens -- the LifeStyle Marquis GP Multifocal (The LifeStyle GP Company, Denver, CO) -- that appears quite helpful in achieving our goals. This design incorporates a multi-aspheric posterior surface with a spherical front surface. It integrates some of the original LifeStyle GP Multifocal design novelties in that it has both an aspheric base curve and an aspheric fitting curve in the midperiphery of the lens called the equivalent
base curve (EQ). The EQ is flatter than the base curve by approximately 0.2mm to promote
per alignment with the midperiphery of the cornea.
The company uses what it calls Curve Differential Optics
(CDO) to determine the aspheric nature of the back surface of a Marquis GP lens. Unlike other posterior aspheric designs, CDO precisely adjusts the reading zones for each of the 17 EQs available, depending on the radius of curvature and add power.
This lens offers a low add for +1.75D or less of spectacle add correction and a high add for +2.00D or greater of spectacle add correction. It features a 9.5mm diameter and is manufactured only in Boston XO (Polymer Technology) material.
Unlike the original LifeStyle GP Design, which must position superiorly central to perform adequately (in fact, its original name was the Hi-Rider lens), the Marquis must center over the pupil in primary position, then translate slightly when the patient's eyes move to the reading position. Figure 1 shows the fluorescein pattern of a successful fit.
For me, a key attribute of this contact lens design is the controlled number of parameters available. If the first lens you choose doesn't achieve the expected fitting result, then you can change only the
EQ, distance vision or add power. Thus, it either fits, or it doesn't.
If it doesn't fit, then you can immediately move on to an alternative design rather than spending time attempting to "tweak" the parameters. If you have a busy practice that caters to busy patients, then this option is a real plus.
Craig Norman is director of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He is a fellow of the Contact Lens
Society of America and is also an advisor to the GP Lens Institute.
Contact Lens Spectrum, Issue: May 2004