Article Date: 6/1/2002

SOFT TORICS
Comparing Soft Toric Contact Lenses
A new toric lens is compared to four other torics on the basis of fitting, comfort, lens location, handling and other measures.
By Robert Campbell, MD, Walter Choate, OD, Robert Davis, OD, David Hansen, OD, Loretta Szczotka, OD, William Vincett, OD

Soft toric contact lenses have frustrated both lens designers and fitters since their introduction more than two decades ago. Not only were early soft toric lenses expensive and inconsistent, they were difficult to fit and troubleshoot.

Despite numerous incremental advances over the years, toric lens fitting has remained challenging. Early generation soft torics forced practitioners to rely on a variety of different and sometimes complicated fitting strategies to achieve acceptable outcomes. As a result, the need for rotational and power compensation has become so ingrained in fitters' minds that complexity and toric soft lenses have become synonymous.

Soft Toric Lens Design

Good optics, physical comfort, rotational stability and first fit success have always been essential elements of soft toric lens design. Improving lens mechanics and clinical performance has remained a daunting challenge and has, until recently, sustained toric lens design as more of an art than a science. Among the reasons for this was the inability to accurately quantify on-eye lens performance or measure the variable effect of different lens parameters and design elements in a clinically meaningful way.

Ocular Sciences Inc and The Institute for Eye Research (IER), located at the Cornea and Contact Lens Research Unit (CCLRU) in Sydney, Australia, jointly addressed the problem of toric lens design, stabilization and first fit success using a scientific approach. Their goals were straightforward:

The definitive result of this analysis and development effort was the design basis for the recently introduced Biomedics Toric lens from Ocular Sciences, a back surface, prism ballasted toric soft lens containing innovative design elements including larger ballast area, uniform horizontal thickness profile, optimal shape for comfort and orientation and smooth, junctionless surface (Table 1).

 

TABLE 1: FEATURES AND BENEFITS OF BIOMEDICS TORIC

DESIGN FEATURE CLINICAL BENEFIT
Wide, annular ballast zone Increased ballast area, enhancing lens location and stability
Horizontal ISO thickness
Reduced stimulus for lens rotation/mislocation, improves lens stability
Constant thickness
(ballast zone)
Consistent on-eye performance for any sphere  power, cylinder power or axis
Optimized overall thickness  Improved comfort, stability and physiology
Continuous smooth front surface Eliminates lens junctions, improves comfort, stability

Study Design

To evaluate the performance of this lens design in a broad based clinical setting, 19 contact lens fitters enrolled a total of 119 existing toric soft lens patients in this multi-center clinical study.

Several hypotheses related to toric lens performance, clinical success, ease of fit and patient acceptance were explored during this contra-lateral direct-comparison of Biomedics Toric lens to other leading toric lenses. Lens performance and clinical outcomes were recorded at baseline and at the end of a two-week wearing period, and subjects completed a questionnaire at the end of the trial. The result of this study explores the suitability of a scientific approach to lens design and offers insight into the next generation of high performance contact lenses.

Materials and Methods

This multi-center clinical study applied a randomized, single masked design to compare the Biomedics Toric to four currently available soft toric lenses. Some 119 subjects, all current successful soft toric lenses wearers, were recruited from 18 geographically diverse practices throughout the United States and Canada. Some 116 subjects completed the study, with three subjects lost to follow-up. The study was divided into four separate cells. Eighteen investigators each independently refit five to nine patients using a Biomedics Toric lens in one eye, and one of four currently available toric soft lenses in the opposite eye. The four cells included Biomedics Toric compared to:

The lens fitted in each eye was masked to the subject; additionally, the contra-lateral comparison lens was fully randomized. All subjects were required to sign an informed consent.

All subjects were screened to ensure that they met eligibility criteria. Enrollment criteria included bilateral astigmatism, age 18 or older and current wear of soft toric contact lenses on a full-time (six hours per day) basis for at least one month prior to the study. Subjects displaying significant anterior segment abnormalities were excluded from the study, as were subjects taking medications which could interfere with contact lens wear or require frequent removal of the lenses.

Patients eligible for the study underwent a baseline fitting and dispensing visit, where habitual lens fit, lens performance and corneal health were evaluated. This evaluation was repeated after fitting of the assigned study lenses, and again after two weeks of full-time wear. At the final two-week visit, all subjects completed a questionnaire that rated handling, comfort, quality of vision and overall satisfaction with the lens in each eye.

Figure 1. Percentage preference for practitioners at the two-week visit.

Results

Practitioner Preference Clinician preference typically reflects clinical performance of a product. The easier a lens is to fit and the better it performs with fewer patient complaints, the more fitters prefer it. Results confirmed a significant preference for Biomedics Toric lens (p<0.0001), with the lens preferred by the practitioner in approximately 71 percent of subjects at the end of two weeks of wear (Figure 1). The next closest performing lens was Frequency 55 Toric, preferred in approximately 22 percent of cases. The strong clinician preference for Biomedics Toric suggests that factors relevant to fitting and patient response have been improved by the introduction of Biomedics Toric.

Figure 2. Mean overall fit acceptance at the two-week visit. 

Lens Fitting Characteristics Figure 2 shows the mean overall fit acceptance ratings for the study lenses. On average, Biomedics Toric was judged significantly closer to the optimal fitting criteria (Grade 4) than the other test lenses. There were no significant differences in corneal coverage between lenses or across visits. There were significant differences between lenses in centration (p=0.03), movement (p<0.01), and tightness (p<0.01), with no significant visit-to-visit effects. Although statistically significant, these inter-lens differences did not reflect clinically significant effects because all lenses were within clinically acceptable ranges at both visits and reflect more on the quality of the acceptable lens fitting.

Figure 3. Percentage of lenses that were within ±5 degrees of the desired axis.

Lens Location Biomedics Toric located closest to on axis at both visits. Figure 3 shows the percentage of lenses that were within ±5 degrees of the desired axis.

The superior lens location and stability of Biomedics Toric was also evident in rotational recovery after a manual 30 degrees displacement (p<0.01). The average angle of recovery compared to an ideal 30 degrees recovery angle is shown for each study lens in Figure 5. Biomedics Toric was closer to an ideal 30 degrees of recovery than was Focus Toric by approximately 8 degrees, and closer than Acuvue Toric by approximately 7 degrees. These differences in orientation performance remained unchanged at the second visit (p=0.21).

Overall Wearer Satisfaction The median ratings for subjects' overall satisfaction and preference responses by lens type are shown in Figure 6. There were significant differences between the lens types in subject ratings of overall satisfaction (p=0.01). Biomedics Toric was rated highest on average (89), followed by Frequency 55 Toric (86), Focus Toric (81), Acuvue Toric (72) and Soflens 66 Toric (68). Good comfort and vision as well as ease of handling are essential ingredients for wearer satisfaction, and differences between lenses for these criteria explain the higher rating of wearer satisfaction in Biomedics Toric.

 

Figure 4. Mean rotational recovery at initial visit. Figure 5. Mean rating of overall wearer satisfaction at the two week visit.

Comfort Patients noted a significant difference between lens types in overall comfort (p<0.01), comfort immediately after insertion (p<0.01) and comfort at the end of the day (p=0.03). In overall comfort, Biomedics Toric rated highest at 88, while Acuvue Toric and Soflens 66 Toric were rated 77 and 76 respectively (Figure 8). In addition to a higher overall comfort rating, Biomedics Toric was preferred over all other test lenses (Figure 9). The results for comfort immediately after insertion are nearly identical to the overall comfort results, both in average ratings and significance level.

 

Figure 6. Overall subject's preferences at the two week visit. Figure 7. Mean rating of overall comfort at the two week visit.

 

Vision In overall quality of vision, there was a significant difference between lens types (p=0.05), with Biomedics Toric rated 87 while Frequency 55 Toric rated 82 and Acuvue Toric 79, on average. Figure 10 shows the patients' percentage preferences for overall vision.

Lens Handling There were significant differences between lenses in subjective ratings of handling; an important factor in patient satisfaction. Biomedics Toric, rated 91 on average, was preferred over Focus Toric (85), Soflens 66 Toric (82) and Acuvue Toric (69).

 

Figure 8. Percentage preferences for subject's overall comfort at the two week visit. Figure 9. Percentage preferences for subject's overall vision at two week visit.

 

Physiological performance To eliminate pre-existing conditions, several indicators of ocular integrity and health were investigated prior to dispensing study lenses, including corneal and conjunctival staining and bulbar and limbal redness. No significant differences in corneal staining were found among the study lenses (p=0.15) or between visits (p=0.37), with all lenses showing little or no corneal staining at either visit. There were also no significant differences shown between lenses in conjunctival staining; however, a significant increase was observed at the second visit (p=0.05).

This observed difference was found with all lenses and, although statistically significant, was not of clinical importance (less than half a grade level on average). A similar result was found for bulbar redness, with no significant differences between lenses (p=0.42) and a moderate increase in redness at the second visit (p=0.08). This again was present with all lenses but not of clinical concern. Evaluating limbal redness, both the lens type and visit effects were significant (p=0.05 and p<0.01, respectively); however, none of the study lenses showed more than mild limbal redness at either visit.

No serious ocular complications were associated with any of the study lenses. Small increases in bulbar and limbal redness, and in conjunctival staining (but not corneal staining) were common to all lenses and were small and clinically insignificant. Similar clinical results suggest that any reported differences in subjective ratings are primarily due to differences in lens design, and are not likely to be confounded by differences in ocular health.

Figure 10. Mean rating of ease of lens handling at the two week visit.

Discussion

This study explored differences in clinical lens performance, fitting characteristics and subjective ratings of lens handling, comfort, vision and overall satisfaction comparing a new scientifically designed lens, Biomedics Toric, to four other state-of-the-art soft toric lenses produced by leading manufacturers.

Both clinicians and subjects significantly preferred Biomedics Toric lens over all comparison lenses, with Frequency 55 Toric being the closest in terms of handling, comfort and clinician preference.

In measures of clinical performance, Biomedics Toric lens aligned closer to "on axis" than the comparison lenses and re-positioned more effectively following deliberate manual rotation with significantly better lens location alignment than Acuvue Toric and Focus Toric. Accordingly, this was reflected in more stable vision ratings with the Biomedics Toric. Differences in subjective ratings of comfort, vision and handling contributed to a higher wearer satisfaction with Biomedics Toric. Biomedics Toric was rated higher than Acuvue Toric, SofLens 66 Toric and Focus Toric lenses for ease of handling. Biomedics Toric provided better overall quality of vision than did Frequency 55 Toric or Acuvue Toric. Biomedics Toric was also preferred to Acuvue Toric because it provided less fluctuation of vision. For all measures of comfort, Biomedics Toric rated highest, followed by Frequency 55 Toric, Focus Toric, Acuvue Toric and SofLens 66 Toric. Of note, Biomedics Toric rated higher than SofLens 66 Toric for dryness throughout the day.

Conclusion

Advances in soft toric contact lenses have made fitting these once complicated lenses easier and have resulted in improved vision, greater comfort and increased safety for our patients who require astigmatic correction. The strong practitioner preference for Biomedics Toric reflected the performance differences observed on a number of clinical measures during this comparative study. The Biomedics Toric represents an achievement in toric lens design and science and the collaboration between a contact lens manufacturer and independent researchers.

Acknowledgement of clinical investigators: Douglas Becherer, OD; Rick Bissonnette, OD; Barbara Caffery, OD; Robert Campbell, MD; Walter Choate, OD; Robert Davis, OD; Paul Gray, OD; John Gysin, OD; David Hansen, OD; Pete Kollbaum, OD; Randy McLaughlin, OD; Scott Mundle, OD; Gregg Ossip, OD; Ellen Rogers, OD; Charles Slonim, MD; Mary Jo Stiegemeier, OD; Tom Stout, OD; Loretta Szczotka, OD; William Vincett, Jr, OD.

Dr. Campbell is the director of refractive services at the Parkwood Eye Center in Elkin, NC.

Dr. Choate is in private practice in Nashville, TN, a charter member of the AOA Contact Lens Section and an adjunct faculty member at Southern College of Optometry.

Dr. Davis has been in private practice for 30 years, lectures on contact lenses and serves as team eye doctor for the Miami Dolphins.

Dr. Hansen, a diplomate and fellow of the American Academy of Optometry, is in private practice in Des Moines, Iowa.

Dr. Szczotka is an assistant professor at Case Western Reserve University Dept. of Ophthalmology and Director of the Contact Lens Service at University Hospitals of Cleveland.

Dr. Vincett Jr. is a contact lens specialist and clinical researcher. He manages a six-doctor private practice in Pittsburgh, Pennsylvania.


Contact Lens Spectrum, Issue: June 2002