Article Date: 2/1/2002

Lens Comparison
A Closer Look at Three Disposable Soft Contact Lenses
A study comparing the clinical and subjective performance of three popular disposable soft contact lenses.
William Miller, OD, PhD, FAAO, Julie Jackson, RN, OD, FAAO, and Thomas C. Prager, PhD, MPH

Disposable soft contact lenses offer many advantages to prospective lens wearers when compared to conventional soft lenses, including better visual performance, lower incidence of deposits, a less complicated care regime, flexible wearing schedules and a readily-available supply of replacement lenses in the event of a lost or damaged lens. As more patients choose disposable lenses and the disposable lens market expands, choosing the right lens for a patient is becoming a greater challenge.

That today's disposable hydrogel soft lenses are very similar in objective measures such as oxygen permeability and physical characteristics complicates this decision. Additionally, in vivo lens performance advantages are difficult to assess using only physical objective endpoints. The decision of which lens to dispense is often then determined by subjective patient responses and/or economic issues.

Methods

This study, conducted in two phases, compares the in vivo performance of patients' masked subjective responses to three popular disposable lenses (Phase I: Acuvue [Vistakon] vs. Biomedics 55 [Ocular Sciences]; Phase II: Acuvue 2 [Vistakon] vs. Biomedics). In each phase, the subjects acted as their own control by simultaneously wearing a different lens in the right and left eye. The evaluation of lens fit and pertinent (functional) clinical findings were performed upon initial lens dispensing and 14 days later. At both visits, subjects received a visual analogue-scaled questionnaire with descriptors. Subjects were asked to rank each of eight subjective categories on a scale from 0 to 100.

Subjects in both phases of the study were unfamiliar with both lenses and the distinct handling marks that show correct inside-out orientation. According to the inclusion criteria, all subjects were required to be free of ocular abnormalities, infections and inflammatory diseases. The initial visit in both phases of this study included an ocular health assessment, refraction, keratometry and measurement of unaided and best-corrected visual acuities. An informed consent form was signed after each subject met the inclusion criteria.

During this initial visit, lenses were fitted and dispensed. All study eyes were corrected to 20/20. Only patients with a clinically-acceptable lens fit and an over-refraction within ±0.50D and <0.75D of astigmatism were accepted into the study. Subjects were advised to continue their usual lens care regimen.

Vertical lens movement was measured using a graticule mounted in the eyepiece of a biomicroscope. The same observer (masked to lens type, subjective responses and objective signs) was used for each subject to reduce variations in measurement.

After two weeks, the subjects returned for a clinical evaluation of the lens fitting relationship and received an eight-category questionnaire to determine the subjective ocular response to lens wear. The questions pertained to subjective lens comfort, quality of vision and ease of handling for each lens. Subjects forfeited the lenses upon completion of the study. Other measurements at this visit included a subjective refraction, Snellen visual acuity and keratometry readings.

Phase I Some 30 adapted lens wearers were recruited for this prospective, masked study. (Mean age=26.23, SD=5.67, 25 females, five males) Each subject was randomly fitted with a Biomedics 55 disposable lens in one eye and an Acuvue disposable lens on the other eye. Acuvue lenses were fit with 8.4mm and 8.8mm base curves, and an 8.6mm base curve was used to fit Biomedics 55 lenses. The power of the fitted Acuvue lenses ranged from ­1.50D to ­7.00D, and the corrective power of the Biomedics 55 lenses ranged from ­1.50D to ­7.50D. (Biomedics 55: mean=­4.18D, SD=­1.81; Acuvue: mean= ­4.16D, SD=­1.76). Each lens type was worn during the patient's waking hours for two weeks.

Phase II Some 31 adapted lens wearers were recruited for this second prospective, masked study. (Mean age=24.97, SD=3.62) Each subject was randomly fitted with a Biomedics 55 disposable lens in one eye and an Acuvue 2 disposable lens on the other eye. Acuvue lenses were fit with 8.3mm and 8.7mm base curves, and an 8.6mm base curve was used to fit Biomedics 55 lenses. The power of the fitted Acuvue 2 and Biomedics 55 lenses ranged from ­1.00D to ­6.50D. (Biomedics 55: mean=­3.80, SD=­1.64; Acuvue 2: mean=­3.78, SD=­1.68). Each lens type was worn during the patient's waking hours for two weeks.

Data Analysis

The raw data in both phases of the study was analyzed statistically using SPSS, Version 10. A paired t-test analysis was used to assess statistical differences between specific subjective categories (raw scores) for the two lens wearing groups. In addition, a Wilcoxon Signed Ranks Test was performed for each phase of the study comparing as a group all eight subjective categories. A P<0.05 was set as our criterion for significance.

Figure 1. Subjective lens insertion comfort at dispensing visit. Vertical Lens Movement (mm)

Results ­ Phase I

Findings at the initial lens fit The mean raw score for initial fitting comfort appears as a histogram in Figure 1. Biomedics 55 was determined to have a statistically higher initial comfort (t=­3.02, P=0.05, paired t-test) in 67 percent of subjects in the study, with 20 percent having no preference and 13 percent preferring the comfort of Acuvue. For 73 percent of subjects, Biomedics 55 provided more movement on blinking during straight-ahead gaze than the Acuvue lens. The average vertical movement of the Biomedics 55 lens was 0.45mm, while Acuvue measured 0.33mm. This difference was statistically significant (t=­5.54, P<0.0001, paired t-test, Table 1).

Findings at two weeks The subjects returned to the clinic following two weeks of daily wear. An evaluation of the lens fit showed that the two lenses continued to provide a clinically acceptable fit. When compared to the initial visit, both lenses showed a small reduction (Biomedics 55 decreased 0.05mm vs 0.07mm for Acuvue) in movement on blinking. However, there was still a highly significant difference in lens movement between lenses. Biomedics 55 moved on average 0.40mm and the Acuvue lens 0.25mm (t = 4.845, P<0.0001, paired t-test, Table 1).

 

TABLE 1:: Vertical Lens Movement (mm)

Phase I  Biomedics 55 (SD) Acuvue (SD) Statistics
Dispensing 0.45 0.33  
Two-week visit 0.40 (0.18) 0.25 (0.12) P<0.005
Phase II Biomedics 55 (SD) Acuvue 2 (SD) Statistics
Dispensing 0.41 0.36  
Two-week visit 0.40 0.36  

  

None of the subjects experienced any adverse reactions with either lens. There was no clinically significant difference between lens types for bulbar or limbal conjunctival injection, neovascularization and corneal staining. Each clinical ocular response was graded on a five-point scale with 0 as normal and 4 a severe response. Without exception, all subjects in the study had a clinical grade between 0 and 1. Also there was no statistical or clinical difference in visual acuity between the Biomedics 55 and the Acuvue lens. Although our sample size of 30 subjects is small, a consistent finding demonstrates that the clinical performance of the two lenses was comparable in regards to self-perceived subjective findings.

Figure 2. Phase I subjective responses.

Eight questions (scored 0 to 100) were used to assess the subjective response to each lens. Queries included: comfort on lens insertion, end of day comfort, burning or stinging, dryness, irritation, visual quality, ease of cleaning and handling. Mean scores for each category are listed in Figure 2. Subjective preference for any given category was judged to be in favor of a particular lens when its mean raw score was greater than its counterpart. Raw scores that were equal were denoted as no lens preference.

After two weeks, insertion comfort raw score was judged to be statistically superior in the Biomedics 55 wearing eye (t = 4.341, P<0.001, paired t-test). The Biomedics 55 was chosen by 70 percent of the subjects in the study, while 27 percent had no preference and 3 percent chose the Acuvue. Biomedics 55 was also the preferred lens (53 percent) for comfort at the end of the day, with 20 percent choosing Acuvue. Some 84 percent had no preference between lens types for the sensation of stinging and burning, four subjects preferred the Biomedics 55, and one subject preferred the Acuvue lens.

Figure 3. Phase I overall lens performance.

In terms of dryness, 33 percent of subjects (P=0.041) preferred the Biomedics 55 while 13 percent preferred the Acuvue lens, and the remaining 54 percent of subjects had no lens preference. Similar findings were seen in the category of lens irritation. Some 33 percent of subjects preferred the Biomedics 55, 20 percent chose Acuvue, and 14 subjects had no preference. Lens handling was statistically higher for the Biomedics 55 (t=2.12, P=0.035, paired t-test). Some 50 percent of the subjects had no lens preference for lens handling, while 40 percent chose the Biomedics 55 and 10 percent chose Acuvue. The quality of vision and lens cleaning problems did not appear to be largely different between the two lens types, with 83 percent having no lens preference for visual quality and 77 percent showing no lens preference with regards to lens cleanliness. Figure 3 summarizes patient preferences for each of the eight subjective categories.

Figure 4 shows the percentage of subjects with a lens preference who chose either the Biomedics 55 or Acuvue lens. Every category clearly shows a preference for the Biomedics 55 lens. An analysis combining all eight subjective categories shows a statistical significance in favor of the Biomedics 55 lens (z=­2.52, P=0.012, Wilcoxon Signed Ranks).

Figure 4. Lens choice for Phase I patients who displayed a lens preference.

Results ­ Phase II

As previously stated, an overall preference is derived when the graded scores are compared between the two lens wearing groups. The lenses were considered equal if the two eyes had comparable (nearly equivalent) subjective questionnaire scores in any one category. An overall lens preference was indicated when the subjective questionnaire score was higher than its counterpart and a ratio computed.

Findings at the initial lens fit Biomedics 55 was rated to have a higher initial comfort raw score (Figure 1, t=­1.57, P=0.13, not significant paired t-test) in 42 percent of study subjects, with 32 percent having no preference and 26 percent preferring the comfort of Acuvue 2. There was no difference in lens movement as only 48 percent of the Biomedics 55 eyes demonstrated more vertical movement on blinking during straight-ahead gaze than Acuvue 2. However, Biomedics 55 did exhibit a greater mean score for vertical movement. Average movement of the Biomedics 55 lens was 0.407mm while Acuvue 2 measured 0.359mm. This difference was not statistically significant (t=­1.56, P=0.13, paired t-test, Table 1).

Findings at two weeks Subjects returned to the clinic following two weeks of daily wear. An evaluation of the lens fit showed that all lenses continued to provide a clinically-acceptable fit. When compared to the initial visit, both lenses showed a very small reduction in movement on blinking (0.001mm and 0.002mm for Biomedics 55 and Acuvue 2, respectively). On average, Biomedics 55 moved 0.403mm and Acuvue 2 moved 0.357mm (t=1.49, P=0.147, paired t-test). In 20 percent of subjects, centration differed between the lenses. In these cases Biomedics 55 was deemed to have better centration (five excellent, one good) than Acuvue 2 (three good, three fair).

None of the subjects experienced any adverse reactions with either lens. There was no clinically significant difference between lens types for evaluations of conjunctival redness, neovascularization, limbal redness or corneal staining. Each clinical ocular response was graded on a five-point scale with 0 as normal and 4 a severe response. All subjects in the study had a clinical grade between 0 and 1. There was no statistical or clinical difference in visual acuity between the Biomedics 55 and the Acuvue 2 lens. Although our sample size of 31 subjects was small, a consistent finding demonstrates that the clinical performance of the two lenses was comparable.

Figure 5. Phase II subjective responses.

As mentioned previously, eight questions (0 to 100) were used to assess the subjective response to each lens. Queries included: comfort on lens insertion, end-of-day comfort, burning or stinging, dryness, irritation, visual quality, ease of lens cleaning and lens handling. Raw subjective scores for each category are listed in Figure 5.

After two weeks, initial comfort was judged to be nearly equal between the two lenses, with 53 percent of the subjects having no lens preference. Of the subjects who had a lens preference, 44 percent preferred Biomedics 55 and 56 percent chose Acuvue 2. End-of-day comfort was judged to be nearly equivalent between the two lenses. However, for subjects with a preference, Biomedics 55 was the preferred lens (64 percent) for comfort at the end of the day, while 36 percent chose Acuvue 2. Some 77 percent of the subjects had no preference between lenses for the sensation of stinging and burning; two subjects preferred Biomedics 55 and five subjects preferred Acuvue 2.

Figure 6. Phase II overall lens performance.

In terms of dryness, 63 percent of subjects had no lens preference. Among those with a preference, 82 percent preferred the Biomedics 55, while 18 percent preferred the Acuvue 2 lens. Similar findings were seen on the amount of lens irritation experienced by the subject with 63 percent of subjects finding the two lenses to be equal. Of those who preferred a lens type, 55 percent chose the Biomedics 55, and 45 percent chose Acuvue 2 lens. Regarding quality of vision, 64 percent of subjects who had a lens preference (11 subjects) chose the Biomedics 55. Lens cleaning problems did not appear to be largely different between the two lens types with 86 percent showing no lens preference with regards to lens cleanliness. Some 33 percent of the subjects had a lens preference for lens handling, with 60 percent choosing the Biomedics 55 and 40 percent choosing Acuvue 2. None of the subjective findings at the two-week visit were statistically significant (P>0.05, paired t-test). Figure 6 summarizes patient preferences for each of the eight subjective categories. Figure 7 summarizes lens preference choices for those subjects who had an initial preference.

To assess general preference for one lens over another, a comparison combining all eight subjective categories was performed which showed a statistical preference for the Biomedics 55 lens over the Acuvue 2 (Wilcoxon Signed Ranks Test, Z=­2.380, P=0.017)

Figure 7. Lens choice for Phase II patients who displayed a lens preference.

Discussion

An important aspect of any practitioner's contact lens practice is the ability to choose the right lens for individual patients. This decision may depend on a variety of factors but is frequently based on previous patients' satisfaction with a given lens.

In the present study, all objective biomicroscopic clinical assessments were nearly equal between the two lenses in each phase. All eyes appeared to tolerate their respective lenses equally well when assessing entities such as limbal injection, bulbar injection and tarsal conjunctival abnormalities. An emphasis, however, was placed on the subjective responses of patients wearing a Biomedics 55 in one eye and either an Acuvue or Acuvue 2 in the contralateral eye.

The initial fitting visit showed that the Biomedics 55 was significantly more comfortable than Acuvue and more comfortable than Acuvue 2 (preferred by a ratio of 1.62:1). In addition, the Biomedics 55 exhibited significantly more vertical movement on a blink than the Acuvue and Acuvue 2 lenses. Both of these positive attributes may promote increased patient satisfaction, the goal of any practitioner. Favorable initial impressions may lead to long-lasting attitudes concerning contact lens success. The greater the satisfaction with the initial fit, the greater the potential for long-term patient acceptance.

After wearing the lenses on a daily wear schedule for two weeks, subjects scored Biomedics 55 higher than Acuvue in all eight subjective categories, with three of these categories showing statistically significant results (insertion comfort, dryness and lens handling). Biomedics 55 also scored higher than Acuvue 2 in seven out of the eight subjective categories (raw scores), with insertion comfort nearly a tie. In terms of insertion comfort after two weeks of wear, a greater proportion of subjects chose the Biomedics 55 lens over the Acuvue lens, while a greater percentage preferred Acuvue 2 over Biomedics 55. During the initial dispensing visit, more patients preferred the initial comfort of the Biomedics 55 lens compared to both the Acuvue and Acuvue 2 lenses. Patients cite this particular subjective quality as the most important variable in lens acceptance.

Patients consider lens handling to be the second most important lens feature. In Phase I, for subjects who showed a preference, the handling of Biomedics 55 was preferred 3:1 over Acuvue, which is an important characteristic for neophytes. Although our study did not focus on the neophyte, mastering insertion and removal is an essential requirement for new users. Additionally, in Phase II, six out of 10 subjects who had a preference chose the Biomedics 55 compared to the Acuvue 2 for handling. Overall, the enhanced design characteristics of the Acuvue 2 lens improved patient preference but still fell short of surpassing Biomedics 55 for lens handling.

Subjects also experienced significantly less dryness while wearing Biomedics 55 vs. Acuvue. Those who cited a difference preferred Biomedics 55 4.5:1 compared to the Acuvue 2. Dryness is a frequently-reported ocular side effect related to contact lens wear; most patients have a greater awareness of dryness near the end of the day. Typically the dryness is not severe enough to discontinue short-term lens wear, but in the long term it may lead to lens failure and patient dissatisfaction. Corneal dryness in lens wearers can be related to material characteristics such as water content and thickness. Other patient factors such as meibomitis, ocular surface disease and lid disease may also play a role in dryness symptoms.

Any of the subjective responses evaluated in this study can result in patient frustration, which may lead to discontinuation of lens wear, a request for a refit with another lens and/or choice of another eye specialist. Subjective findings from this study can help practitioners choose the proper lens for their patients in order to enhance long-term acceptance of soft contact lens wearers. The Phase I of the study indicated that Biomedics 55 surpassed Acuvue in all subjective categories with selected categories showing a statistically significant advantage. Phase II indicated a preference for Biomedics 55 when the eight subjective categories were combined and compared. It also showed that Acuvue 2 fared better than its predecessor lens Acuvue. However, Biomedics 55 still outperforms Acuvue 2 in nearly all of the subjective categories, resulting in at least an equivalent if not more acceptable lens for the patient.

To receive references via fax, call (800) 239-4684 and request document #79. (Have a fax number ready.)

This study also was supported, in part, by grants from Research to Prevent Blindness, Inc. New York, New York, and NEI Core Grant EY10608

Dr. Miller is on faculty at the University of Houston College of Optometry. He is a member of the American Optometric Association and serves on its Journal Review Board.

Dr. Jackson is an Assistant Professor at the University of Houston College of Optometry and Coursemaster of the second year optometry Contact Lens Laboratory.

Dr. Prager is the Vale Asche Russell Professor of Ophthalmology at the University of Texas Medical School, Houston, and director of the Freeman Clinical Electrophysiology/Ultrasound unit at the Hermann Eye Center.

 


Contact Lens Spectrum, Issue: February 2002