Comparing Hydrogel and Silicone Hydrogel Torics
TORIC LENS STUDY
Comparing Hydrogel and Silicone Hydrogel Torics
This study compared toric lenses for daily wear and monthly replacement.
By S. Barry Eiden, OD, FAAO, & Robert L. Davis, OD, FAAO
Dr. Eiden is co-founder of EyeVis Eye and Vision Research Institute and president of a private group practice in Illinois. He has a financial interest in Alternative Vision Solutions, LLC, is a consultant or advisor to CIBA Vision, CooperVision, SynergEyes, Alcon and SpecialEyes and has received research funds from Vistakon and CooperVision.
Dr. Davis is co-founder of EyeVis Eye and Vision Research Institute. He practices in a suburb outside Chicago. He is an advisor or consultant to CooperVision and SynergEyes, has received research funds from CooperVision and has a proprietary interest in SpecialEyes and Alternative Vision Solutions.
Soft toric contact lens fittings have increased with expanded toric lens parameters and designs. In the United States, soft torics now account for more than one-third of new daily wear fits (36 percent). This suggests that many practitioners are more satisfied with soft toric lens performance than in the past.
Silicone hydrogel contact lens designs continue to grow as the lens material of choice and now account for more than 42 percent of new soft daily wear fits in the United States. However, discontinuation from contact lens wear is still a major issue, with 15-to-30 percent of contact lens patients dropping out each year. The primary reasons for lens wear termination remain dryness and discomfort. Other factors cited for contact lens discontinuation include inconvenience and poor vision.
To satisfy patient needs and minimize discontinuation, lens performance must meet a wide range of criteria. Some soft toric lens manufacturers have specifically promoted silicone hydrogel lenses for managing dry eye symptoms associated with contact lens wear. A successful toric lens must meet a wide range of criteria including clear and stable vision, sustained wearing comfort, good physical handling characteristics and appropriate physiological eye health response. Silicone hydrogel soft toric lenses may address the issues related to oxygen permeability, but has this been at the expense of clinical performance related to comfort and vision in these designs? This study compared the clinical performance of three silicone hydrogel toric lenses to that of two hydrogel toric lenses.
This was a multi-center, randomized, patient-masked, controlled-crossover study to evaluate and compare performance characteristics of three silicone hydrogel toric lenses (Acuvue Advance for Astigmatism [Vistakon], Air Optix for Astigmatism [CIBA Vision] and PureVision Toric [Bausch & Lomb]) with two hydrogel toric designs (Proclear Toric [CooperVision] and Biomedics Toric [CooperVision]) over one month of daily wear use.
Key variables included comfort, vision quality, subjective symptoms, slit lamp findings and forced choice patient preference at the conclusion of the study.
The study received IRB approval from the Oaklawn IRB, in Oaklawn, Ill. Subjects, who consented to participate, completed the five-month daily wear study wearing five contact lens designs (Table 1) bilaterally for one month in random succession at four U.S. clinical sites. Subjects were fitted with toric contact lenses and objective and subjective evaluations (Table 2) were performed at baseline, at dispensing, and after one month of wear for each pair of lenses. All lenses were replaced monthly. Two of the toric lens designs tested — Acuvue Advance for Astigmatism and Biomedics Toric — are recommended by their respective manufacturers for two-week replacement versus monthly replacement. We evaluated these two popularly prescribed lens designs for monthly replacement due to patient use patterns demonstrating that two-week prescribed replacement lenses are commonly replaced at longer intervals. Follow-up visits were all conducted after six hours of wear.
Patients completed a dry eye questionnaire at baseline and at one month. Overall subjective lens preference was rated at the final visit using forced choice preference for the most comfortable lens, the lens that provided the best vision quality, and the best overall rated contact lens.
All subjects used the same multipurpose disinfecting solution (MPDS) regimen, Opti-Free Replenish (Alcon).
Inclusion Criteria Participants were current soft contact lens wearers age 18 or older with symptoms and/or reduced wearing time from contact lens-induced dryness and/or lens discomfort. Spherical refractive error ranged from –1.00DS to –6.00DS (limited due to Air Optix for Astigmatism parameter availability at the time of the study). Refractive astigmatism of at least 0.75DC, but not greater than 1.50DC, with axes of 90 degrees/180 degrees ±20 degrees (also due to the limitations of Air Optix for Astigmatism parameter availability at the time of the study) was required.
Statistical Analysis Parametric tests were performed using F- tests for multiple means and pooled t-tests were used where appropriate. Chi-square tests were used for categorical data.
Following is the baseline data.
Subject Demographics Fifty-three subjects were enrolled and completed the five-month study wearing five pairs of soft toric lenses bilaterally for one month in random succession on a daily wear basis. Seventy percent of the subjects were female, 87 percent of the subjects were Caucasian. The remaining 13 percent were Asian, African-American and Hispanic. The mean age of subjects was 37.3 years (±1.7 years).
Habitual Lenses All subjects wore daily wear, soft toric contact lenses prior to entering the study. One in four wore SofLens 66 Toric (B&L); nearly half wore silicone hydrogel torics. The remainder wore other hydrogel toric lens designs.
Subjective Symptoms at Baseline All subjects experienced dryness symptoms or discomfort with their habitual lenses. Eighty-seven percent had dryness symptoms after two hours of lens wear. Nineteen percent of subjects had been told they had dry eye by their eyecare practitioners. Forty-two percent of the subjects categorized themselves as having dry eye.
Figure 1 summarizes reported symptoms (subjects could select more than one symptom). More than two-thirds of the subjects reported sensation of dryness, grittiness or burning with their habitual contact lenses.
Figure 1. Symptoms experienced with habitual lenses (n = 53).
After one month of daily wear, participants reported on vision quality, comfort and handling.
There were no significant differences in average wearing time among the five designs of lenses. The range of average wearing time was a minimum of 11.5 hours per day with PureVision Toric to a maximum of 12.8 hours per day with Air Optix for Astigmatism. There were also no significant differences in wearing time until dryness symptoms occurred, ranging from 4.4 hours with PureVision Toric to 6.7 hours with Air Optix for Astigmatism. Most lens performance measures were equivalent among the five soft torics following one month of lens wear each. Some key measures, however, showed statistically significant differences (Figure 2). Subjects ranked PureVision Toric significantly less comfortable (P=0.04) than Proclear Toric, Biomedics Toric and Acuvue Advance for Astigmatism. Acuvue Advance for Astigmatism was reported significantly less comfortable (P=0.04) than Proclear Toric and Air Optix for Astigmatism.
Figure 2. Vision quality, comfort and handling after one month DW (n = 53).
Subjects rated Acuvue Advance for Astigmatism most difficult to handle (P=0.03); Biomedics Toric was rated easiest to handle (8.7 on a 0-to-10 scale compared to 6.2 for Acuvue Advance for Astigmatism.) There were no significant differences in vision quality or visual acuity measures among lenses; vision quality (0-to-10 scale) ranged from 7.0 with Acuvue Advance for Astigmatism to 7.7 with Proclear Toric.
We also recorded subjective symptoms at one month. Proclear Toric wearers reported that their eyes felt "least tired" (P=0.03, score of 0.88 on a 0-to-5 scale). The highest score was 1.52 for Acuvue Advance for Astigmatism. Patients also reported that their eyes felt less tired at the end of day with Proclear Toric compared to PureVision Toric, Biomedics Toric and Acuvue Advance for Astigmatism (P=0.04, score 1.3 compared to 2.22 for Acuvue Advance for Astigmatism). Air Optix for Astigmatism wearers reported the "least intense feeling dryness" after two hours of wear, although this was not statistically significant (score 0.83 [±0.16]). The highest score was reported with Acuvue Advance for Astigmatism at 1.65 (±0.20), reflecting a greater feeling of dryness.
Wettability and Deposition Proclear Toric, Acuvue Advance for Astigmatism and PureVision Toric had significantly lower (better) mean pre-lens tear film quality scores compared to Biomedics Toric and Air Optix for Astigmatism (P=0.0008, Figure 3). There were no statistically significant differences for mean non-invasive breakup time, invasive breakup time or phenol red thread test scores.
Figure 3. Mean Pre-Lens Tear Film Quality Scores after one month DW (n = 53).
Lens Fit Characteristics We did discover statistically significant differences in dynamic fit characteristics. Biomedics Toric and Air Optix for Astigmatism demonstrated less movement on pushup (tighter) than other lenses (P=0.00007). Mean scores for Biomedics Toric and Air Optix for Astigmatism were 1.66 (±0.19) and 1.58 (±0.19) compared to 2.2 (±0.11), 2.29 (±0.12) and 2.14 (±0.14) for Acuvue Advance for Astigmatism, PureVision Toric and Proclear Toric, respectively. Acuvue Advance for Astigmatism decentered inferiorly significantly more frequently than did the other lens designs (P<0.001). More than half of Acuvue Advance for Astigmatism lenses decentered inferiorly (55.32 percent). Air Optix for Astigmatism and Biomedics Toric positioned inferiorly significantly less than average (4.9 percent, P<0.01 and 13.6 percent, P<0.05, respectively). Air Optix for Astigmatism positioned temporally more frequently than did others (P<0.05, 39.0 percent). We noted no differences in centration nasally or superiorly, or in mean lens decentration among the five lens designs.
Lens Rotation There were significant differences in rotation characteristics among lens designs. More PureVision Toric (P<0.05) and Proclear Toric (P<0.001) lenses rotated temporally while Acuvue Advance for Astigmatism (P<0.05) and Air Optix for Astigmatism (P<0.001) showed the least temporal rotation. We found no significant differences in nasal rotation among lenses.
Slit Lamp Findings There were significant differences in slit lamp findings (P<0.05, Figure 4).
Figure 4. Slit Lamp Findings after one month DW (n = 53).
Proclear Toric showed a lower frequency of epithelial edema, epithelial microcysts, and bulbar and palpebral conjunctival hyperemia. PureVision Toric demonstrated higher frequency of corneal staining. Acuvue Advance for Astigmatism had a higher frequency of palpebral conjunctival hyperemia.
Forced Choice Lens Preference at the End of the Study Subjects rated Proclear Toric as the best overall lens most frequently (28 percent, P<0.05); Air Optix for Astigmatism was least preferred overall (P<0.05, Figure 5). Vision clarity with Air Optix for Astigmatism was ranked best least often (P<0.05); 12 percent of patients rated it as best vision clarity compared to at least 20 percent with the other lenses. There were no statistically significant differences in rating for the most comfortable lens (forced choice). Subjects choosing which lens was most comfortable ranged from a high of 23 percent for the Proclear Toric to a low of 16 percent for the Biomedics Toric.
Figure 5. Subjective preference at exit visit (n = 53).
With the introduction of silicone hydrogel contact lens materials and designs, manufacturers have promoted an array of proposed advantages of these lenses. Increased oxygen transmission associated with silicone hydrogels has been suggested to result in safer and more comfortable contact lenses. Manufacturers of silicone hydrogel contact lenses have also specifically promoted these lenses to manage dry eye symptoms associated with contact lens wear. Practitioners know from clinical experience that a successful lens must meet the criteria of clear and stable vision, sustained comfort throughout the lens wearing time, good physical handling characteristics, and appropriate physiological eye health response to lens wear.
This study compared the performance of three silicone hydrogel toric lenses and two hydrogel toric lenses worn for one-month daily wear replacement. The results of this study suggest that increased oxygen transmission alone does not result in improved lens performance. Subjective measures of lens performance evaluated in this study included ratings of visual clarity, on-eye lens comfort, dryness symptoms associated with lens wear, lens handling characteristics, results of a dry eye questionnaire, and a forced choice lens preference decision. Objective measures included biomicroscopy findings, tear production as measured by phenol red thread testing, tear film stability as measured by invasive and non-invasive tear film breakup times, tear film stability over the lens surface, and physical lens fit assessment of rotation, centration and movement. The hydrogel lens designs evaluated in this study performed equally well or better in the various subjective and objective measures evaluated.
Of the five toric designs evaluated in this study, subjects ranked Proclear Toric most frequently as the best overall lens and Air Optix for Astigmatism least frequently as the best overall lens in the forced choice section. The other three lens designs were rated very closely to each other as second, third and fourth best overall lens.
The other two aspects of lens performance evaluated in the forced choice section included most comfortable design and design that provided the best clarity. There was no statistically significant difference in the frequency of selection of the most comfortable lens among the five lens designs tested. However, analysis of comfort scale ratings among lens designs determined that subjects rated PureVision Toric and Acuvue Advance for Astigmatism significantly lower on a comfort scale versus Proclear Toric and Air Optix for Astigmatism.
For the forced choice of the lens that provided the best clarity, subjects selected Air Optix for Astigmatism significantly less frequently than the other four designs. There was no significant difference in the selection frequency of the other four designs for the best clarity lens. Interestingly, a review of the subjective visual clarity scale rating found no significant difference among any of the five lens designs. In addition, a number of other subjective and objective measures failed to find any significant difference among any of the five lens designs. These included: corrected visual acuities, average lens wearing time, the number of hours of lens wear before appreciation of dry symptoms, mean phenol red thread test results, mean invasive and non-invasive TBUT scores, and mean lens centration (although Acuvue Advance for Astigmatism demonstrated significantly more inferior decentration than did the other four lenses).
The dry eye questionnaire results found few significant differences among the lens designs. Only responses to the frequency of appreciation of the eyes feeling tired (both during the day and at the end of the day) differentiated any of the designs. The Proclear Toric was found to induce tired eyes at a significantly lower frequency compared to the other designs. Also, Air Optix for Astigmatism was found to have significantly lower intensity of dry eye sensations during the first two hours after waking in the morning versus the Proclear Toric, Acuvue Advance for Astigmatism and Biomedics Torics.
Evaluation of subjective lens handling determined that subjects ranked Acuvue Advance for Astigmatism less easy to handle versus the other designs. The Biomedics Toric and Air Optix for Astigmatism demonstrated significantly less movement in comparison to the other three lens designs. Evaluation of lens rotation demonstrated that the PureVision Toric and Proclear Toric lenses rotated significantly more in a temporal direction than did the other three designs. The Proclear Toric, PureVision Toric and Acuvue Advance for Astigmatism showed a significantly lower ranking of pre-lens tear film (PLTF) quality compared to the Biomedics Toric or Air Optix for Astigmatism. Lower PLTF indicates better quality, better wetting properties and less debris.
Biomicroscopy findings were different among the lenses evaluated. The Proclear Toric resulted in lower frequencies of epithelial microcysts and epithelial edema, as well as lower frequencies of bulbar and palpebral hyperemia. The PureVision Toric had a significantly higher frequency of corneal staining than did all of the other lenses. Acuvue Advance for Astigmatism had a significantly higher frequency of palpebral hyperemia compared to the other four lens designs.
The performance results of the five toric lens designs evaluated in this study suggests that silicone hydrogel materials do not necessarily result in better functioning lenses. Based on overall patient lens preference, the best lens selected overall was the Proclear Toric. The Proclear Toric also demonstrated the best biomicroscopy outcomes compared to the other four designs evaluated. In a prior comparative toric lens study we published in February 2008 titled "Comparing Two-Week Toric Contact Lenses," where the frequency of lens replacement was two weeks, the Air Optix for Astigmatism and Biomedics Toric designs significantly outperformed the Acuvue Advance for Astigmatism design. In this study, subjects selected Air Optix for Astigmatism as the best lens significantly less frequently than all other lens designs. Also in this study, both the Air Optix for Astigmatism and the Biomedics Toric designs demonstrated poorer PLTF findings. This suggests that these two lens designs may function significantly better on a two-week replacement schedule versus a monthly replacement schedule.
Of the five designs evaluated in this study, only the Proclear Toric, Air Optix for Astigmatism and PureVision Toric are recommended for monthly replacement by their manufacturers. The remaining two designs are recommended for two-week replacement. However, it's common knowledge that most patients prescribed lenses for two-week replacement actually replace them far less frequently. In addition, a number of practitioners prescribe many two-week lenses for monthly replacement. It was for these reasons that this study evaluated the performance of two-week lens designs worn for one-month daily wear replacement. The results of the study tend to support the manufacturers' suggested replacement schedule. The exception is Air Optix for Astigmatism which CIBA recommends for monthly replacement. However during its pre-market evaluation studies it was suggested for two-week replacement.
Critical characteristics that result in acceptable and continued lens wear include excellent and consistent visual performance and appropriate on-eye lens comfort. Proper physiological and ocular health response is the final characteristic in the triad of the formula for successful wear. Silicone hydrogel lens materials provide exceptional oxygen permeability compared to hydrogel materials. Current designs of silicone hydrogel toric lenses do not exceed the performance of one hydrogel toric lens as measured by the parameters of this study. Future studies will be needed to assess whether the increased-oxygen-transmission attributes of silicone hydrogel torics will result in improved physiological eye health response over long periods of time in daily wear lens use. Until then it is apparent that at least one current hydrogel toric design can perform as well as or better than current silicone hydrogel toric lenses. CLS
The study was conducted via a non-restricted research grant from CooperVision to EyeVis Eye and Vision Research Institute. The authors also would like to thank Natalie Cogswell and Caroline Blackie, OD, PhD, for data retrieval and statistical analysis.
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #160.
Contact Lens Spectrum, Issue: March 2009