A Planned Replacement Toric Soft Lens in Trial and in Practice

BY JOSEPH B. STUDEBAKER, O.D., F.A.A.O.
JUNE 1997

How can you successfully and profitably incorporate planned replacement of toric soft lenses into your practice? This practitioner's recent experiences with CooperVision's Preference Toric lens will provide some useful insights.

One of the most significant changes to contact lens practice over the past few years was the introduction of disposable and planned replacement spherical contact lenses. A natural next step is to extend the planned replacement option to patients with astigmatism.

Advances in toric soft lens design -- parameter reliability, manufacturing techniques and fitting strategies -- have paralleled the earlier developments of frequently replaced spherical soft contact lenses. Although a planned replacement system of contact lens management is not a panacea for all astigmatic patients or for every contact lens practice, my findings from a recent clinical investigation of a quarterly replaced lens design and later use of the design and replacement regimen in my practice make me optimistic about the potential benefits of planned replacement for astigmatic soft lens patients.

THE LENS IN TRIAL

In early 1994, I was one of seven practitioners in the United States and Canada who conducted a three-month clinical investigation of what was then termed a 'tetrafilcon toric' lens design, the predecessor of CooperVision's Preference Toric lens for quarterly replacement. This lens has nominal base curves of 8.4mm and 8.7mm, an overall diameter of 14.4mm and is composed of tetrafilcon A, a 42.5 percent water, nonionic FDA Group I terpolymer. Tetrafilcon A is highly regarded by many doctors and researchers for its relatively high resistance to protein deposition and for its excellent durability and optical clarity. An additional benefit of the investigational lens was its basis upon the time-tested CoastVision Hydrasoft toric lens, which incorporates cast-molded posterior surface toricity, a lathe-cut front lens surface, eccentric lenticulation and prism ballasting.

For the study, I randomly selected 10 patients from my practice (there were 70 subjects in the study as a whole), a mixture of new and established toric soft lens wearers. I fitted the lenses empirically and instructed the patients to use Bausch & Lomb's ReNu multipurpose solution for cleaning, rinsing, storing and disinfecting their lenses. I did not specifically recommend enzymatic cleaning but left this to each patient's discretion. Most of the patients found enzyming unnecessary.

One of my initial reservations about the empirical fitting of a planned replacement toric soft lens involved the basic predictability of toric lens fittings. Even relatively recent studies indicate that most contact lens practitioners prefer to use diagnostic lenses to fit toric soft lenses. I, too, was rather dubious about the practical reliability of empirically fitting Preference Toric or any new toric lens. Today, I'm no longer a skeptic.

During this investigation, five of my patients attained 20/15 distance visual acuity and five attained 20/20 acuity with their initial pair of empirically dispensed lenses. Now, nearly three years and 200 patients later, I find the clinical reliability with empirical fitting of Preference Toric lenses to be adequate for up to 80 percent of all patients, leaving perhaps 20 percent of patients who are better served through diagnostic trial fitting. Because of this, I now employ an empirical fitting approach to a substantial majority of my new toric soft lens patients as well to most refits.

EMPIRICAL FITTING WORKS

One reason that the Preference Toric lens is especially well suited to empirical fitting is its exceptional rotational stability. Most patients exhibit less than five degrees of rotation, and rotational translation between blinks usually does not exceed one to two degrees. The base curve and diameter combinations of this lens design are very forgiving and provide adequate fitting characteristics for a broad range of lid-to-cornea relationships and corneal topographies. Spherical powers range from +4.00 to -6.00 in 0.25D steps. Cylinder powers are available from -0.75 to -2.25 in 0.50D steps. Cylinder axes are available around the clock in five-degree increments.

The lenses are provided in screw-top vials in four-packs. The company offers a 100-day, 100 percent warranty on the first lens fit. If exchanges or final fitting refinements are required, you can return all four lenses, or you can use the recently announced free trial program to trial fit prior to purchasing the four-pack.

With the advent of corneal topography systems, I have found that the odds of successful empirical fitting have improved. We topographically screen most candidates for toric or specialty contact lens fitting and this allows us to more judiciously employ toric soft lens designs in patient management. With data from the topographer and analyses of the tangential corneal radii, we can identify patients who have unique peripheral corneal characteristics that may not permit satisfactory toric rotational stability or centration with certain lens designs. An example might be an astigmatic patient whose corneal astigmatism is isolated to a relatively small area of the central cornea and whose peripheral corneal topography is relatively spherical, thus minimizing the stabilizing effects of a posterior surface toric lens. This patient might be better served by a front surface toric design where rotational stability is provided by the interaction of the eyelids with the 'thin zones' of the lens design and is not dependent upon corneal toricity.

THE LENS AS A PROBLEM-SOLVER

I find that the Preference Toric lens is a particularly good problem-solver for my patients with dry eyes because its material provides excellent deposit resistance, permitting safe quarterly lens replacement and a simplified contact lens care regimen.

In my experience, this lens is also useful for toric soft lens wearing patients who are highly critical observers. The methylmethacrylate (MMA) component of the tetrafilcon terpolymer provides relatively greater material rigidity and, therefore, excellent optical clarity.

Be sure to consider the slightly more rigid attributes of the tetrafilcon material when you provide patients with initial wear instructions, particularly if a patient formerly wore a less rigid or a higher water content lens material. I advise my patients that their lenses may seem somewhat more rigid compared to other lens materials and that they may experience slightly more lens awareness for the initial 48 hours of lens wear. I temper this by adding that, over the long term, this material provides enhanced optical performance, lens durability and lens handling characteristics.

THE LENS IN PRACTICE

In our practice, we dispense an annual supply of toric soft lenses along with a six-month supply of a multipurpose solution system at the completion of the patient's fitting. We instruct the patient to return for follow-up evaluation in six months when we dispense the next six months' supply of solutions. We charge a global fee to cover the examination, contact lens management, lenses and solutions/care supplies. In determining our fees, we try to keep patient costs for quarterly replacement of toric lenses the same as for conventional toric lens wear and let the simplicity, superior ocular performance and convenience of the system do the selling.

We prefer the three-month replacement cycle because it integrates nicely into our practice's existing contact lens follow-up schedule of semiannual visits. To bolster patient compliance, we preappoint all contact lens follow-up visits in our office computer. With this mechanism and the added incentive for patients to return to obtain their next six months' supply of contact lens care products, we find that very few patients fail to return as scheduled for follow-up care.

Today's contact lens practitioner must always be seeking out improved and more efficient ways of rendering quality eye care to patients. This recent combination of new and improved soft toric manufacturing techniques, deposit resistant materials and a planned replacement management approach is an excellent and safe one for patients and doctors alike. In my experience, this represents a convenient regimen that enhances patient compliance and, therefore, eye health. It is also a system for the care of astigmatic contact lens patients which optimizes both patient satisfaction as well as office efficiency for busy contact lens practitioners and their staffs. CLS

References are available upon written request to the editors at Contact Lens Spectrum. To receive references via fax, call (800) 239-4684 and request document #21. (Be sure to have a fax number ready.)

Dr. Studebaker is in a group optometric practice specializing in contact lenses and primary eye care in Englewood, Ohio. He currently chairs the member benefits committee of the Ohio Optometric Association.