Finding Success with Multifocal Contact Lenses
BY JEROME S. LIEBLEIN, OD
The statistics show that around 40 percent of the current U.S. population is presbyopic. This percentage is expected to grow to about 50 percent by the end of this year. Presbyopes are the largest growing segment of the population. Many of these patients are already wearing contact lenses and are ready to move into the multifocal modality.
So, where do we go from here? If you're like me, you've tried all of the different bifocal and multifocal contact lenses as they have been introduced to the market. They all promise to be the one that really works. Your expectations soar, you invest in a fitting set, and then comes the crushing disappointment of reality. Although this seems to happen repeatedly, we keep trying because we really need a multifocal contact lens that works. In your discussions with other contact lens practitioners, you'll find that some will tell you about their fantastic results, while others will swear that good results are impossible.
So why do some practitioners get better results than others? The answer is easy: they have large fitting sets. In order to test this theory, I asked Fused Kontacts to provide my practice with a 100 lens count fitting set of their Tangent Streak No Line Multifocal RGP contact lens design. Using this set, I was able to achieve an 80 percent success rate with only 2.8 visits per patient.
The Contact Lens
The Tangent Streak No Line contact lens is a simultaneous vision RGP multifocal with an aspheric back surface. It has an eccentricity of around 1.0, a spherical peripheral curve and a center distance design. Due to the unique posterior design, the true base curve is not used as the fitting curve.
Fitting the Patient
To determine the fitting base curve, if corneal toricity is less than 1.00D, go 0.25D flatter than steep "K." If corneal toricity is greater than 1.00D, select a fitting curve 0.4D steeper than the flat K. Since the fitting curve is approximately 0.16mm flatter than the true base curve, subtract 0.16 from the fitting curve to calculate the prescription. An example of this process is provided in Table 1.
Evaluating the Fit
The Tangent Streak multifocal contact lens is designed to provide maximum acuity when well-centered (Fig. 1). The more decentration, the greater the plus power produced, which makes it an easy lens to fit. If your overrefraction shows plus, the lens is obviously off-center.
FIG. 1: Tangent Streak No Line, 7.65 best fit.
Steepening/lowering (Fig. 2), or flattening/raising (Fig. 3) the fitting base curve should help position a decentered contact lens. As a general rule, always evaluate the acuity binocularly. This should be done for all bifocal and multifocal contact lens patients. Simultaneous contact lens patients always see better after they have worn their lenses for about one week.
FIG. 2: Tangent Streak No Line, 1.50D too flat.
FIG. 3: Tangent Streak, 1.50 steep.
Fifteen successful patients (3 male, 12 female) were randomly selected to support my theory. Powers prescribed ranged from -7.00D to +6.75D, with cylinders up to 2.00D. One of the patients has keratoconus with very steep, distorted mires.
In all cases, binocular visual acuity was never worse than 20/25. All of the patients responded as to how well they were able to see. Two reported failures were both due to the position of the lenses. The third failure, a previous soft lens wearer, achieved 20/20 distance and near acuity, but dropped out due to comfort issues.
The results of this study are the best that I have ever experienced with a gas permeable simultaneous multifocal lens. The Tangent Streak No Line Multifocal lens offers an easy fitting design with a high degree of success. I attribute my 80 percent success rate, with only 2.8 patient visits (see Fig. 4) and two pairs of lenses, (see Fig. 5) to the design of the lens and to the large fitting set. It's easy to have success with a well-made product when all you need is to go to a lens tray, pick out the proper power contact lens, and dispense.
FIG. 4: Most patients only require 2.8 visits.
FIG. 5: Most patients require only two pairs of lenses.
Dr. Lieblein is a vision director for Pacific Care and is also an executive manager of Cleinman Performance Partners. He is a past president of the California Optometric Association and the American Society of Contact Lens Specialists, and is past chair of the American Optometric Association Contact Lens Section.
|Patient's K-reading||42.00 @ 180 x 43.00 @090|
|Patient's Distance Rx||+0.75D|
|Fitting Base Curve||42.75D (7.90mm)|
7.9mm - .16mm = 7.74mm (43.62D)
|Order:||7.90mm fitting base curve with -0.87 Rx|
|The Tangent Streak No Line provides an add power of up to +2.25D, or typically about a +0.50D more compared to other similar designs.|