Article Date: 3/1/2005

SOFT TORIC MULTIFOCAL LENS
Improve Fitting Success for a Soft Toric Multifocal Lens
Fitting patients with a multifocal lens of similar design can improve success with a soft multifocal toric lens.

By Kenneth A. Young, OD

Statistics indicate that the United States currently has more than 100 million presbyopes. Of those, 99 percent don't wear contact lenses. With 10,000 people turning 50 years old every day, we can estimate that approximately 4.5 million new presbyopes enter the market each year. Great opportunities abound for eyecare professionals in the multifocal arena.

Figure 1. Essential Soft Toric Multifocal design.

Recently, soft bifocal and multifocal contact lenses have made great strides in their development and ability to provide binocular vision correction for distance, near and intermediate performance. Eyecare professionals are looking for an easy-to-fit, comfortable lens with sufficient add correction for near vision and minimal compromise to distance vision, all without sacrificing intermediate vision performance. They seek a product that delivers a high first fit success rate and a fitting regimen that reduces chair time.

Hope for Astigmatic Presbyopes

In the past, astigmatic presbyopic patients had little choice when it came to correcting their vision. But with today's advancements in soft contact lens manufacturing technology, multifocal and bifocal soft contact lenses have become an attractive and viable alternative to spectacle correction for their presbyopic needs. However, such lenses may prove difficult to fit, require large amounts of chair time and result in a loss of binocular vision correction and intermediate visual performance.

Patients who have an astigmatic error in addition to their presbyopia present special challenges. Fortunately, eyecare professionals now have another option for contact lens correction in this hard-to-fit demographic with the introduction of the Essential Soft Toric Multifocal (Blanchard Contact Lens, Inc.) contact lens (Figure 1). Table 1 lists its parameter availability.

 

TABLE 1 Essential Soft Toric Multifocal Parameters

Sphere Powers ­6.00D to +9.00D by 0.25D
(­8.50D to +6.50D distance vision)
Cylinder Powers ­0.75D to ­3.00D in ­0.25D steps
Base Curve/Diameter 8.8mm/14.8mm, 8.5mm/14.4mm, 8.2mm/14.0mm
Axis 180º ±30º and 90º ±30º in 1º steps

 

Testing a Screening Method

Three private practice eyecare offices as well as my own participated in a study to evaluate a five-step screening guideline (see sidebar on p. 43) designed to assist the fitting of the Essential Soft Toric Multifocal using the Quattro Aspheric Soft Multifocal lens (Blanchard) as the initial trial (screening) lens. The study authors chose 28 patients from a population of current successful soft toric contact lens patients who now require presbyopic vision correction, excluding monovision patients. The study evaluated the ability to provide astigmatic presbyopic patients with acceptable distance, near and intermediate vision using the Quattro trial (screening) lens in concert with a sphero-cylindrical over-refraction. If the "Quattro Screening Method" is a viable alternative to empirical fitting, then we could assume that the additional cylinder correction available with the Essential Soft Toric Multifocal would allow practitioners to successfully fit astigmatic presbyopic patients with a significant reduction in chair time and would provide patients with vision performance comparable to their current toric soft lenses and near vision performance with minimal compromise of intermediate vision.

Figure 2. Anterior surface aspheric power profile for both lens designs.

A Look at Lens Design

Both study lenses are simultaneous vision lenses featuring an identical aspheric multifocal optic on their respective anterior surfaces. Blanchard uses its patented proprietary "S-Form" lathing manufacturing process to create a true aspheric optic or an "S-Curve" anterior surface aspheric power gradient (Figure 2). S-Form Lathing technology compresses more effective add correction (up to +2.50D) within a usable optical area, beginning at the axial center of the anterior lens surface. The Essential Soft Toric Multifocal incorporates a posterior toric base curve, double slab-off anterior design with axis markings at three o'clock and six o'clock (Figure 3).

Performing the Screening Fit

We began the fitting process by selecting the appropriate lens power of a Quattro lens according to the suggested manufacturing guidelines using only the spherical component of the refraction. Following lens equilibration (20 minutes), we performed a sphero-cylindrical over-refraction for distance and near vision. If the patient could achieve acceptable visual acuity at distance, near and intermediate, then we ordered the new lens with the resulting combination of the trial lens and the over-refraction. If the patient couldn't achieve acceptable vision at either distance or near, then we discontinued the fitting.

Figure 3. Optics of the Essential Soft Toric Multifocal.

Study Results

We screened 28 patients into the study, and 89 percent of them completed the study. Overall, we ordered 86 lenses and achieved a first-fit success rate of 32 percent. We had only a 35 percent warranty exchange rate for the study and we replaced 30 lenses mainly because of incorrect axis orientation.

We also discovered that some study patients who had low amounts of cylinder didn't need the Essential Soft Toric Multifocal because they performed well with the Quattro. The aspheric multifocal optic present on the Quattro lens effectively masked small amounts of cylinder correction for seven percent of the eyes fit.

The binocular visual performance of the study group was outstanding with 85 percent achieving 20/25 or better for distance, 75 percent achieving 20/30 or better for intermediate and 83 percent achieving 20/30 or better for near.

Screening patients to predict success may eliminate excessive lens orders (unnecessary warranty exchanges) and significantly reduce chair time. Our study shows that the Quattro trial (screening) method is effective and more proficient than empirical fitting in successfully fitting Essential Soft Toric Multifocal lenses for astigmatic presbyopes.

Additional Study Participants:

Blanchard Contact Lens, Inc. funded this study.

 

Dr. Young is in private practice in Brentwood, TN. For the past 10 years, he's also worked as a clinical investigator for the FDA and many different contact lens, solution and pharmaceutical manufacturers. Dr. Young is a member of the American Optometric Association's Contact Lens Section and serves as an adjunct faculty member at Southern College of Optometry and UAB.

 

 

 

Essential Soft Toric Multifocal Screening Guide
 

STEP 1. Convert the prescription to minus cylinder.

STEP 2. Determine Quattro trial lens power by adding half of the patient's add power to the sphere power.

STEP 3. Choose Quattro Base Curve:

  • 8.4mm (45.50D to 47.00D)

  • 8.8mm (40.00D to 45.00D)

STEP 4. Place the Quattro trial lenses on the patient's eyes and allow them to equilibrate.

STEP 5. Perform a complete sphero-cylindrical over-refraction (try to achieve a balance):

  • If the patient can't achieve acceptable vision performance for all focal points, then discontinue the fitting process.

  • If the patient achieves acceptable visual performance for all focal points, then order the Essential Soft Toric Multifocal by combining the Quattro trial lens power and the sphero-cylindrical over-refraction.

 



Contact Lens Spectrum, Issue: March 2005