Retinal Physician Article Submission Guidelines-Prescribing for Astigmatism and Presbyopia

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Article Date: 9/1/2008

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Comparing Two Silicone Hydrogel Toric Lenses
SILICONE HYDROGEL TORICS

Comparing Two Silicone Hydrogel Toric Lenses

This study evaluated the clinical performance and subjective preferences for two silicone hydrogel torics.

By Jeffrey Sonsino, OD, FAAO


Dr. Sonsino is the chair of the American Optometric Association's Anterior Segment Committee and an assistant professor at Vanderbilt Eye Institute in Nashville, Tenn.

In the past, contact lens options for astigmatic patients were limited. In recent years, however, newer designs and extended parameter ranges for soft toric contact lenses have made lens wear a possibility for most patients who have astigmatism. Also, the introduction of silicone hydrogel toric contact lenses has brought the benefits of high oxygen transmissibility to astigmatic patients.

Two available silicone hydrogel toric lenses are Air Optix for Astigmatism (CIBA Vision) and Acuvue Advance for Astigmatism (Vistakon). Newer to the market, Air Optix for Astigmatism contact lenses are silicone hydrogel lenses made of 67 percent lotrafilcon B and 33 percent water. These lenses have a permanent, biocompatible plasma surface treatment and a Precision Balance 8|4 Design intended to provide for rapid fitting, stability and comfort. Acuvue Advance for Astigmatism contact lenses are also silicone hydrogel lenses, in this case made of 53 percent galyfilcon A and 47 percent water. These lenses feature the Accelerated Stabilization Design, which is reported to use the pressures of the blinking eye for lens stability and to help prevent rotation.

I practice in an academic medical center. Approximately 75 percent of my patients are referred for complex problems, including difficulty with previous contact lens fits. For all of the patients I see in my practice, I feel that I can't afford to use materials that are not the best current technology. Because of this, I was interested to see how Air Optix for Astigmatism lenses compared to Acuvue Advance for Astigmatism lenses in terms of clinical performance and subjective preference.

Study Design

As part of a multicenter trial, my colleagues and I evaluated the clinical performance of Air Optix for Astigmatism lenses and Acuvue Advance for Astigmatism lenses. Primary variables in this clinical study included visual acuity, axis orientation, subjective ratings and preference for vision, comfort, handling and overall preference. Biomicroscopy variables and lens surface characteristics were also evaluated.

We enrolled 97 soft toric contact lens wearers at 11 sites in the United States in this prospective, randomized, single-masked, cross-over study. Patients wore each lens brand for four weeks on a daily wear basis, with examinations after two weeks and four weeks. Acuvue Advance for Astigmatism lenses were replaced at the two–week visit while patients wore the same pair of Air Optix for Astigmatism lenses for the entire four-week study period. Clear Care was used for cleaning and disinfection. Patients were masked to the lens manufacturer, the product brand and the lens replacement cycle throughout the trial. All patients included in the study were toric soft contact lens wearers who had worn their current contact lens brand for at least three months for daily wear. We enrolled no current wearers of Acuvue Advance for Astigmatism or Air Optix for Astigmatism.

Results

At both the two-week and four-week visits, subjective ratings for constant, stable vision were significantly better for Air Optix for Astigmatism compared to Acuvue Advance for Astigmatism (Figure 1), and patients reported fewer symptoms of fluctuating vision with Air Optix for Astigmatism (p<0.001, 95 percent lower confidence limit >0). Subjective ratings for handling were also significantly better for Air Optix for Astigmatism at both visits (Figure 2). We found no statistical differences for any comfort variables evaluated (Figure 3). At the end of the trial, patients reported a preference for Air Optix for Astigmatism for overall handling and for overall preference (Figure 4).

Figure 1. Subjects preferred Air Optix for Astigmatism for overall vision and for constant, stable vision at both two weeks and four weeks.

Figure 2. Subjects preferred Air Optix for Astigmatism for overall handling at both two weeks and four weeks.

At the two-week visit, we found that Air Optix for Astigmatism lenses oriented closer to 90 degrees compared to Acuvue Advance for Astigmatism (p<0.001, 95 percent upper confidence limit <0), and that Air Optix for Astigmatism lenses demonstrated statistically better centration (p=0.024) and lens wetting (p<0.001, 95 percent upper confidence limit <0).

Figure 3. There were no statistical differences for any comfort variables evaluated in this study.

Figure 4. Subjects in this study rated Air Optix for Astigmatism higher for overall handling and overall preference.

Lastly, at both the two-week and four-week visit, Air Optix for Astigmatism lenses showed minimal front surface deposits, with the mean grade for front surface deposits significantly lower than that for Acuvue Advance for Astigmatism at four weeks.

Discussion

Stability is important for achieving a positive visual outcome and overall success with a toric lens. Ideally, lenses should be very stable, with little rotation during blinking and rapid recovery to the natural position following manual displacement. The Air Optix for Astigmatism lens is described as having a Precision Balance 8|4 design, with the thickest parts of the lens at the 8 o'clock and 4 o'clock positions. I've found that this design provides exceptional stability, with consistent orientation and fit performance, and our study demonstrated this through better axis orientation compared to Acuvue Advance for Astigmatism. In addition, the rapid orientation and excellent stability of Air Optix for Astigmatism provided patients with clear, consistent vision, which subjects expressed in this study with higher ratings for constant, stable vision compared to Acuvue Advance for Astigmatism.

Deposit resistance influences long-term wearing success of a lens. In this study, Air Optix for Astigmatism provided superior deposit resistance with the mean grade for front surface deposits being lower than that of Acuvue Advance for Astigmatism. Deposit resistance is important because deposits on the anterior surface of a lens may create mechanical stimulation of the palpebral conjunctiva, which can lead to contact lens papillary conjunctivitis (CLPC).

Also of importance to patients is comfort. The design of Air Optix for Astigmatism, with a thinner area at the 6 o'clock position (relative to other toric lenses with prism-ballast design), helps minimize the interaction with the lower lid, which can help provide a more comfortable lens-wearing experience. The previously mentioned plasma surface treatment and a constant contour edge design also can contribute to improved lens comfort. In this study, subject ratings for comfort after application for Air Optix for Astigmatism averaged 8.0 or higher at all study visits.

Long-term comfort is perhaps more difficult to achieve, as evidenced by patients' frequent complaints of end-of-day dryness with many lenses on the market. However, our study found that long-term comfort is likewise very good with Air Optix for Astigmatism. The average overall comfort rating for Air Optix for Astigmatism remained high at two weeks and four weeks.

It goes without saying that a lens must not adversely affect the health of the eye. As one measure of eye health, I pay particular attention to corneal vascularization because it is pathognomonic for hypoxic stress on the anterior ocular surface. Hypoxic stress affects the cellular structure of the cornea, after which more serious complications such as infiltrates and infection can occur. Air Optix for Astigmatism, made from lotrafilcon B (Dk = 110), offers the highest oxygen transmissibility of any available soft toric lens, including Acuvue Advance for Astigmatism (galyfilcon A, Dk = 60), which I feel is important for eye health.

Summary

In this study, patients expressed an overall preference for Air Optix for Astigmatism. This may be the result of a combination of factors. First, rapid stabilization and good initial comfort may make a positive first impression during fitting. Furthermore, the handling of Air Optix for Astigmatism may reduce patient frustration at application and removal. The lens' on-eye lens stability can provide constant, stable vision. In fact, in my experience Air Optix for Astigmatism has significantly better rotational stability than other lenses I've evaluated. And finally, according to our study Air Optix for Astigmatism also provides long-term comfort and excellent deposit resistance. CLS

This study was sponsored by CIBA Vision Corporation.

For references, please visit www.clspectrum.com/references.asp and click on document #154.



Contact Lens Spectrum, Issue: September 2008

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