Article Date: 6/1/2005

SOFT TORIC CONTACT LENSES
 Attaining Vision and Comfort with Soft Torics
With ease of fit and so many design and material options, soft torics are an excellent choice for astigmats.
By Marcus M. Devlin, OD

Have soft torics really become so easy? Actually, the answer is "Yes." No longer should practitioners experience long, sleepless nights contemplating the extended chair time they need to fit soft toric contact lenses. Fear of multiple follow-up visits eating away at your schedule should no longer exist. The reason? Soft torics are painlessly easy to fit. The available lens materials, wear schedule options, lens designs and powers provide practitioners with a more-than-adequate opportunity for fitting success.

Improve Your Patients' Vision

I believe toric lenses are absolutely necessary for proper vision care. Over the past five years, we've experienced a steady increase in the overall number of soft toric fits. However, the number of soft toric contact lens wearers continues to fall well below the number of patients who have correctable astigmatism. Considering the many contact lens wearers who have cylinder values greater than –0.75D, we're still missing a tremendous opportunity. Each time we perform a refraction and the final result reveals cylinder, we should consider a toric contact lens. Proactive approaches to soft toric fitting will not only help patients see more clearly, but will increase the value of our practices. With the vast improvements in manufacturer technology, better lens reproducibility and various design options of today's lenses, all practitioners should take advantage of giving patients the best vision possible.

You can and should consider any of the past arguments against the use of soft toric lenses in favor of spherical lenses as obsolete by today's standards. Visual fluctuation, limited cylinder powers and lack of different lens designs are no longer excuses to avoid fitting astigmatic patients. Contact lens manufacturers realize the importance of creating products that allow practitioners to fit soft toric lenses with extreme confidence. So stop worrying about failure and lost chair time, and don't make "20/happy" the endpoint visual acuity for your astigmatic patients. Soft toric contact lenses are a reasonable and viable option for the regular astigmatism patient. So let the fitting process begin.

Soft Toric Fitting Basics

Following are a few basic guidelines for a successful soft toric fit:

What makes soft toric fitting so easy? The answer lies in the pre-fit knowledge that we now have. Accurate keratometry readings, an accurate refraction, detailed history and careful slit lamp examination help determine the proper diagnostic lens. And because of appropriate pre-fit preparation (determining lens design, material, replacement schedule, etc.), the diagnostic lens often becomes the dispensed lens. This technique takes all guesswork out of the process. In turn, the actual fitting may take only minutes.

Choosing a Lens Design

Lens designs vary, thus giving practitioners the opportunity to match the appropriate lens to each individual patient. Following are some of the lens options from a few major manufacturers.

CooperVision offers a range of lenses that can generally cover most corneas. For example, the Vertex Toric provides consistent, reliable results for relatively average corneal shapes. This back-surface toric is currently offered only in an 8.6mm base curve. Because the average corneal curve is generally from 43.00D to 45.00D, the Vertex Toric works well most of the time.

For corneas that may be a little too steep or too flat for the Vertex lens, the Frequency 55 Toric is available in base curves of 8.4mm and 8.7mm. The Frequency 55 Toric is also a back-surface toric. The Proclear Toric provides yet another option and features an 8.8mm base curve for flatter corneas. CooperVision also offers the Ocular Sciences Biomedics 55 Toric with a standard base curve of 8.7mm.

CIBA Vision offers the Focus Monthly Toric in base curves of 8.9mm and 9.2mm. Although these values would indicate adequate correlation with flatter corneas, I find that this lens tends to perform well for both flat ranges and for more average curvature ranges (43.00D+). Another option from CIBA is the Focus Dailies Toric. It features a standard base curve of 8.6mm. It's available in only 90-degree and 180-degree axes and cylinder power of –0.75D. Practitioners won't find any laser markings on these lenses because they're simply prepackaged at axis 90 or 180.

Bausch & Lomb offers the SofLens 66 Toric, which has the highest water content of the lenses in this article (with the exception of Focus Dailies Toric) at 66 percent. It features a back-surface toric design and is available with an 8.5mm base curve and up to –2.75D of cylinder. The FDA recently approved the Purevision Toric for use in the United States. This is a low-water content, high Dk/t lens. Initial parameters may be limited, but I expect B&L to expand them fairly quickly.

Vistakon currently offers two toric lens options. The Acuvue Toric has a dual thin zone design, which helps reduce lens interaction with the lower lid. This lens comes in a standard base curve of 8.7mm. I find this lens particularly useful when fitting ATR corneas. The newest toric lens on the market is the Acuvue Advance for Astigmatism. This lens has an accelerated stabilization design and comes in an 8.6mm base curve. The stabilizing design is based on accelerated slope of thickness zones that prevent unbalanced interaction with the lids. The theory is that when the lens is stabilized and in position, it works with the lids during the blink rather than against them. This design is unlike prism-ballasted lenses that can dislodge when interacting with the lower lid. Both toric designs feature a UV blocker.

Choosing a Lens Material

Because toric lenses are appropriate for patients of virtually any age, selecting the lens material is important. Even the healthiest of patients can eventually present with dry eye symptoms after lens wear. End-of-day comfort continues to be a major hurdle for practitioners and patients to overcome. The lenses I've mentioned each have a different material matrix and vary quite dramatically in water content.

Feedback in our clinic continues to show a reduction in contact lens dropouts secondary to dry eye. CooperVision is helping our battle against dry eyes with the Proclear Toric. A blend of 62 percent water content along with phosphorylcholine has earned the lens an indication for dry eye from the FDA and through patient satisfaction.

Vertex Toric and Frequency 55 Toric have water content values of 55 percent each, as does the Ocular Sciences Biomedics 55 Toric. As when fitting any Group IV lenses, choose patients wisely in terms of lipid content in the tear film. Patients who tend to produce excess amounts of lipid may fare better in a non-ionic material such as Proclear Toric.

CIBA Vision has a simple solution to lens protein and lipid buildup: Simply throw the lenses away after each use. The Focus Dailies Toric uses a 69 percent water content material as well as the CIBA Light Stream Technology. Patients tend to find this lens comfortable, and many find the opportunity to dispose of lenses after one use very appealing. I tend to fit this lens particularly for the age range of 12 years to 25 years, although obviously not exclusively. Any patient who has an active lifestyle is an excellent candidate for daily disposable lenses.

The SofLens 66 Toric is a Group II material that blends the comfort of a higher water content lens with the more deposit-resistant non-ionic matrix. I use this lens on patients of just about any age, with careful attention to tear lake. Patients who have excellent tear lake and overall tear quality generally do well wearing the Soflens 66 Toric. The silicone hydrogel (balafilcon) Purevision Toric is our first continuous wear toric lens to receive approval. Once launched, its 30-day continuous wear schedule may prove a wonderful new option for soft toric wearers.

Vistakon's two toric lens options drastically differ in material makeup. The Acuvue Toric consists of a Group I lens material that has a water content of 58 percent, while the new Acuvue Advance for Astigmatism adopts the Hydraclear matrix popularized by the Acuvue Advance spherical lens. The Acuvue Advance for Astigmatism manages to control comfort as a result of its silicone hydrogel material (galyfilcon A) with Hydraclear.

High Cylinder Options

Most of the lenses discussed thus far have upper cylindrical values of –1.75D to –2.75D, varying with each manufacturer. Cylinder values over –2.00D have always proven a topic of discussion. Do soft torics provide stable vision at higher cylinder powers? Should you use prism ballast or thin zones? Must you go to a conventional lens? Are GPs the best option? We'll continue to debate the answers to all of these questions, but following are a few lenses that are available and work well for me.

CooperVision offers two lens types that not only correct high astigmats, but offer patients a frequent planned replacement lens. The Frequency 55 Toric XR is a back-surface toric that has a cylinder range from –2.75D to –5.75D in 0.50D steps. Axis values range from zero to 180 degrees in five-degree steps. Another option for even higher amounts of cylinder is the Preference Toric XR. Cylindrical values range from –2.75D to –9.75D Axis values also range from zero to 180 degrees in five-degree steps. This is usually dispensed as a quarterly replacement lens.

Choose Replacement Schedules with Care

Proper lens replacement schedules vary greatly from patient to patient. Practitioners have different views on how far to stray from manufacturer recommendations. I personally stay fairly close to them. Because of the vast availability of disposable lenses, practitioners often overlook the importance of the micromanagement that may be necessary for long-term success. Quite often comfort is the reason for patient success or failure.

The lenses I've discussed include daily replacement, two-week replacement, one-month replacement including 30-day continuous wear and three-month replacement. With the variety of anterior segment complications that exist, you must choose the final lens type with careful consideration for each patient.

The Future of Soft Torics

Beginning with Acuvue Advance for Astigmatism and soon the PureVision Toric, a wave of silicone hydrogel toric lenses is soon to come. Higher Dk/t values will provide yet another improvement in lens design, and more lenses may join PureVision as overnight or continuous wear toric options this year.

In addition, lens stabilization will continue as a focus of improvement for lens manufacturers. Expect others to follow Vistakon in an attempt to create novel lens designs to help achieve better stabilization and less visual fluctuation.

In conclusion, make soft toric lens fitting a primary service in your practice.  Patients will appreciate your expertise as well as the clear vision you have provided to them.  When the refraction reveals significant astigmatism, reach for the toric lens.

All lens parameters appeared in Vol. 22 No.2 of Tyler's Quarterly Soft Contact Lens Parameter Guide, March 2005, and the Contact Lenses and Solutions Summary.  X-Cel, Gelflex and Westcon also manufacture toric soft lenses that are widely accepted.

Dr. Devlin is the Cornea and Contact Lens Resident at The Eye Institute of The Pennsylvania College of Optometry and is the Chief of Refractive Services for a private ophthalmological practice in Elkins Park, PA

 

Contact Lens Spectrum, Issue: June 2005