A Clinical Comparison of Two Toric Lenses
A Clinical Comparison of Two Toric Lenses
A patient study compared a widely prescribed toric HEMA lens with a new toric silicone hydrogel.
By Glenda Secor, OD, FAAO
Dr. Secor is in private practice in Huntington Beach, CA. A Fellow of the American Academy of Optometry and Diplomate of the Cornea and Contact Lens Section, she is the current Immediate Past Chair of the Cornea and Contact Lens Section.
By nature, many clinicians are skeptical of change. When a contact lens patient is happy, visual acuity is satisfactory and the eye looks healthy, we tend to stick to the status quo.
Yet my role as an investigator in a clinical comparison of a widely prescribed toric HEMA lens with a new toric silicone hydrogel lens taught me that I can always do more for patients — even when they don't initially perceive that their contact lens wearing experience could be improved.
Seven U.S. eyecare practices selected patients who were successfully wearing SofLens66 Toric hydrogels (Bausch & Lomb, alphafilcon A with 66 percent water content). These patients had been wearing this lens on a daily wear basis for at least three months. A total of 63 patients participated in the study.
Patients were masked to the test lens brand and manufacturer. At the baseline visit, investigators collected clinical data regarding the SofLens66 Toric. Patients completed a subjective questionnaire and then were fit with Air Optix for Astigmatism lenses (CIBA Vision, lotrafilcon B with 33 percent water content).
Clinicians re-examined patients at two weeks and four weeks. At all visits, visual acuity was measured and the clinician performed biomicroscopy and evaluated lens fitting and lens surface characteristics. Patients also completed a subjective questionnaire at each visit.
The results were consistent with my clinical experience during the study. The key statistically significant differences between Air Optix for Astigmatism and SofLens66 Toric included both objective and subjective results. Visual acuity was statistically better with Air Optix for Astigmatism (p<0.001, non-inferiority, 95 percent 1-sided upper confidence limit <0). Objective measures of lens centration and rotational behavior were significantly different. Table 1 presents the four-week results.
At the four-week visit, patients rated Air Optix for Astigmatism higher on subjective variables relating to comfort, vision and the whiteness of their eyes (Figure 1).
Patients rated most problems they experienced as less frequent with Air Optix for Astigmatism than with SofLens66 Toric. Figure 2 shows these results at four weeks.
Significantly more patients preferred Air Optix for Astigmatism overall as well as for comfort, vision and handling at the four-week visit. These results are shown in Figure 3.
As a clinician, I consider the SofLens66 Toric to be an effective and useful lens. The SofLens66 Toric patients I enrolled all appeared to be successful wearers before the study.
Of course I was aware of and appreciate the oxygen permeability of the silicone hydrogel material. But in the course of the study, I found that the Air Optix for Astigmatism lens design also provides stable visual acuity and is easy to fit.
CIBA Vision describes the lens design as Precision Balance 8|4, with the thickest parts of the lens located at the 8 o'clock and 4 o'clock positions to enhance stability and offer consistent rotation. I found the design on target in terms of positioning quickly and providing the desired visual acuity. The SofLens66 Toric is also a very stable lens design, but in my experience Air Optix for Astigmatism performed better.
The Air Optix for Astigmatism lens oriented and settled quickly, which helped to streamline the fitting process. Following lens application, I found that I could quickly identify which patients were likely to succeed, which can help reduce chair time.
Air Optix for Astigmatism performed better on subjective comfort ratings. A feature that likely contributed to comfort was the thin area at 6 o'clock, where the lower lid contacts the lens. Because toric lenses are always thicker than spherical lenses, a thin area such as this may make a difference when the patient first wears it. It also helps to maximize the oxygen transmissibility in this inferior region, where clinicians most commonly observe neovascularization with toric lenses (corresponding to the thicker, prism-ballasted portion of some toric designs). Another design element that may contribute to the comfort of Air Optix for Astigmatism is the constant contour edge design.
Along with the lens design, the oxygen transmissibility and the surface of Air Optix for Astigmatism may help contribute to comfort. To counter the hydrophobic nature of silicone, CIBA Vision adds a permanent, biocompatible plasma surface treatment that creates a smooth, continuous surface that resists deposits.
Air Optix for Astigmatism also demonstrated an advantage in handling over SofLens66 Toric. I perceived that the lotrafilcon B of Air Optix for Astigmatism did not curl like some other silicone hydrogel toric lenses do.
The improved corneal health that clinicians have observed with spherical silicone hydrogel lenses also seems apparent with Air Optix for Astigmatism. In the four weeks of the study, I noticed less limbal blood vessel engorgement. In most patients, I observed a whiter, healthy-looking eye.
Figure 1. At the four-week visit, patients rated Air Optix for Astigmatism higher on subjective variables relating to comfort, vision and the whiteness of their eyes.
Figure 2. At four weeks, most patients rated the problems they experienced as less frequent with Air Optix than with SofLens66 Toric.
Figure 3. Significantly more patients preferred Air Optix overall at the four-week visits, and for comfort, vision and handling.
The study data indicated that patients were already satisfied with the vision they achieved with SofLens66 Toric. However, they reported better vision with Air Optix for Astigmatism. The lens is designed to promote stability, and the improvement in vision made a big enough difference that subjectively, patients noticed it as well.
In this study comparing Air Optix for Astigmatism with a leading HEMA lens, I found that the design and superior oxygen transmissibility of Air Optix for Astigmatism provided a clear advantage from both clinician and patient perspectives. I would call silicone hydrogel toric lenses a shift in paradigm. This is where we are going with a new generation of toric lenses.
A contact lens with the many benefits that I believe Air Optix for Astigmatism has is critical to my practice. In today's competitive environment, it's important for clinicians to offer the newest, latest and greatest. Patients come to me seeking the latest technology and are willing to try new options when the outcome is much more predictable and successful. The new Air Optix for Astigmatism lens gives me a strong tool for exceeding my patients' expectations.
I've had great success with Air Optix for Astigmatism with low against-the-rule patients (–1.00 –1.00 ×090) who are thrilled to have their small amount of cylinder corrected with a silicone hydrogel toric. I've found that the lens offers them a stable option that dramatically improves their acuity and comfort. The handling in a low power has been great, and these patients are happier than with spherical lenses.
CIBA Vision has increased the available axis and cylinder options for this lens since the completion of this trial, which makes it that much more useful. I am looking forward to additional power parameter expansions. CLS
The study was sponsored by CIBA Vision.
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #150.
Contact Lens Spectrum, Issue: May 2008