Despite soft contact lenses (CLs) being available for several decades, usage rates remain low compared with the proportion of the population needing refractive correction. An estimated 130 million people wear CLs worldwide compared with 2 billion people requiring some type of distance correction.1 In North America, approximately 12% of the population wear CLs, a statistic that has changed little during the past 5 years, despite significant advances in the CL industry during this time.1 This stagnation in the CL-wearing population is because of a number of factors, foremost of which is that 24 to 34% of those who begin CL wear discontinue2–4 primarily because of ocular discomfort, which accounts for 49 to 64% of all instances.2,4–7 Ocular discomfort is also an issue for those who remain wearing CLs. Approximately 35% of CL wearers report dissatisfaction with lenses, and 82% of these individuals cite ocular symptoms as a reason for their dissatisfaction.3 Using a Web-based survey that assessed ocular comfort for three consecutive days, Lazon de la Jara et al.8 reported that 35% of full-time CL wearers experienced a consistent decrease in ocular comfort by the end of the day on all 3 days, with 29% not changing and 35% showing inconsistent results.
Ocular symptoms are also more frequent in soft CL wearers than non–lens wearers.6,9,10 Several studies have shown increases in dryness10,11 and decreases in ocular comfort8,12 the longer CLs are worn. Because end-of-day comfort is significantly worse in those who discontinue compared with those who remain wearing lenses,5 the implication is that “symptomatic” wearers who consistently have reduced end-of-day ocular comfort are at risk of discontinuing lens wear. Conversely, the incidence of CL discontinuation might be reduced if symptomatic wearers were to experience an improvement in end-of-day comfort.
For many clinicians, the most obvious means of addressing this problem is to switch either the CL type or lens care product (LCP) because each of these components has a range of physical properties13,14 that can potentially impact ocular comfort. There are conflicting reports on the impact different CLs have on the comfort response.15–18 So far, as the LCP is concerned, whereas some studies have indicated that advantages can be gained by switching from one to another,19 others have found no effect,20 been of short-term duration,21,22 or used substitution-type designs in which the habitual LCP is replaced by an alternative.23,24 The problem with the latter approach is that interpretation of the outcome is confounded by the tendency of participants to respond positively to any new situation particularly if they are involved in a clinical study.25 It might, of course, be argued that such studies are valid because substitution is exactly what typically occurs in practice. However, such a view would condemn both clinicians and wearers to relying on potentially temporary advantages introduced purely by the change while remaining ignorant of the true benefit of the specific intervention. Notwithstanding the difficulties involved with interpreting the various studies, the lack of clear direction in the literature may be an indication that the magnitude of any such gains might be rather limited in real terms. It would then seem reasonable to ask what the practical performance limits available to such switching strategies might be. If an intervention of this kind is to have clinical use, it needs to produce a subjectively appreciable outcome for the wearer. Thus, knowledge of the maximum benefit that might be achieved is critical to establishing a basis on which to judge the value of switching in the overall management of CL-related discomfort. Accordingly, the present study attempted to answer the question: how big a change in subjective comfort might it be appropriate to expect under the most favorable circumstances? Knowledge of the maximum benefit that might be achieved is critical to establishing a basis on which to judge the value of switching in the overall management of CL-related discomfort.
This was a prospective, single-masked (subject), crossover, bilateral, randomized clinical study conducted at the International Clinical Trials Centre of the Brien Holden Vision Institute in Sydney. To be eligible, subjects had to be experienced CL wearers, at least 18 years old, be myopic in both eyes and correctable to at least 20/40 (6/12) distance visual acuity with spherical hydrogel CLs, and have no ocular or systemic findings that would prevent safe CL wear. Subjects were not dispensed CLs if a successful lens fit was not achieved or if visual acuity with CLs was worse than 20/40 (6/12).
The CL-LCP combinations used in this trial were selected based on the outcomes of a series of studies conducted at the Institute, in which groups of approximately 40 subjects wore each of a range of CL-LCP combinations for 3 months, attending for assessment on three scheduled occasions. In all, there were 42 individual studies involving 1610 subjects. Ocular comfort data, including comfort on insertion and at the end of the day, were obtained at each scheduled visit. From this experience, it was possible to select the best and worst performing CL-LCP combinations from among those tested by establishing the percentage of subject visits in each trial that showed a less than 1-point decrease between the comfort score on insertion and that at the end of the day. On this basis, the combination of galyfilcon A (Acuvue Advance; Johnson & Johnson Vision Care, Jacksonville, FL) with a polyhexanide LCP (AQuify; CIBA Vision, Duluth, GA) (combination 1) had the highest percentage (41%), whereas balafilcon A (PureVision; Bausch + Lomb, Rochester, NY) with polyquaternium-1, myristamidopropyl dimethylamine + TearGlyde (OPTI-FREE Replenish; Alcon, Fort Worth, TX) (combination 2) had the lowest percentage (12%). The assumption was that switching participants between these two combinations would yield comfort responses that approximated the extremes of those experienced during contemporary CL wear.
A sample size of 24 subjects was required to demonstrate a statistically significant paired difference in subjective ratings of 1 ± 1.5 between the two crossed over CL-LCP combination stages, after adjusting for a 15% dropout rate, with 80% power at the 5% level of significance. The study enrolled a primary group consisting of subjects who were “symptomatic” CL wearers. These were taken from the cohort of 1610 subjects who took part in the original series of trials and were defined as those who experienced at least a 1-point or more comfort decrease (1 to 10 scale) between insertion and the end of the day at all three scheduled visits. A secondary group of nonsymptomatic CL wearers was also enrolled, and these were defined as those who experienced no decrease in end-of-day ocular comfort compared with comfort on insertion at any scheduled visit, provided that at least two visits were attended. Subjects who participated in multiple trials and satisfied the criteria for both symptomatic and nonsymptomatic CL wearers were considered to be inconsistent in their responses and so were excluded from this study.
A Quality of Life Multidimensional Scale26 (QoLMS) was completed by subjects at the baseline visit and before any other study procedures. This scale assessed dimensions related to an individual’s quality of life, including physical status, psychological state, cosmesis, and personality traits. The QoLMS was composed of five subscales, namely, frequency of visual/ocular symptoms, tolerance of visual/ocular symptoms, psychological state, personality, and cosmesis, as well as assessing patient satisfaction with the current treatment for correcting refractive error.
Before commencing lens wear, subjects entered a 48-hour washout period during which CLs were not worn. Subjects were initially allocated to one of the two CL-LCP combinations based on a crossover design randomization scheme generated through http://randomization.com/. Lenses appropriate to the individual’s visual needs were inserted straight from the lens pack. One base curve was used for each lens type: 8.3 mm for galyfilcon A and 8.6 mm for balafilcon A. Contact lenses were worn for seven consecutive days after lens dispensing (8 days in total) for a minimum of 8 hours per day, with the allocated LCP used for disinfection, storage, and rinsing. Daily lens insertion was directly from the LCP. Disinfection and storage with LCP commenced after lens removal on day 1. Subjects were not informed as to whether they were categorized as symptomatic or nonsymptomatic, neither were they aware of the relative rankings of the CL-LCP combinations in terms of comfort performance.
At the end of 8 days’ wear, subjects again entered a 48-hour washout period. The above procedure was then repeated with the second CL-LCP combination.
Slit lamp biomicroscopy was used to assess ocular health (before lens dispense on day 1 and at the conclusion of each stage on day 8) and lens fitting (primary gaze movement [in millimeters], primary gaze lag [in millimeters], and tightness on push-up [in percent]) at lens dispensing.
A take-home questionnaire (THQ), completed on days 2, 4, and 6, was used to assess ocular comfort, ocular dryness, and ocular symptoms. Ocular comfort and ocular dryness data were obtained immediately after lens insertion and after 2 and 8 hours of wear, whereas ocular symptoms were obtained after 8 hours.
Ocular comfort and dryness were assessed using a numeric rating scale (NRS) scored on a 1 to 10 interval in 0.1-point steps, with 1 = poor and 10 = excellent. For comfort ratings, a higher score indicated better comfort; for dryness ratings, a higher score indicated less dryness.
Ocular symptoms (blurred, fluctuating or variable vision, lens awareness, and ocular dryness) were assessed based on frequency of occurrence. They were recorded on a 0 to 4 scale, with 0 = I do not have this symptom (none), 1 = I seldom notice this symptom (trace), 2 = I sometimes notice this symptom (mild), 3 = I frequently notice this symptom (moderate), and 4 = I always notice this symptom (severe).
Several measures were undertaken to ensure that subjects were compliant with completing their THQ on the appropriate day and at the appropriate time. The THQ for each day of a stage was printed on different colored paper (day 2, green; day 4, pink; day 6, blue), with the specific day and time points also clearly printed in large font. The date each THQ was due to be completed was handwritten on the THQ in front of the subject at the first visit of each stage, and each subject was instructed to record on the THQ the actual date of completion for each time point. Subjects were instructed to return their THQ at the final visit of each stage on day 8. An SMS reminder was sent the day before the visit to remind subjects of their appointment and to return the THQ.
The THQ used was simple to complete because it only required two numeric ratings to be recorded at each of the three time points on a given day and an additional slightly more complicated questionnaire after 8 hours of wear. The subjects in this study were experienced clinical trial participants who understood the importance of the THQ to the study and were all familiar with completing questionnaires from previous trial participation.
The study received ethics approval through a local human research ethics committee and was conducted in accordance with the principles of the Declaration of Helsinki.
Symptomatic and nonsymptomatic subjects were compared for differences in demographic variables using χ2 and group t tests. Quality of life scores were summed within each subscale of the instrument. The total scores of each subscale were compared between symptomatic and nonsymptomatic subjects using group t tests. Within each subject strata (symptomatic and nonsymptomatic), ocular comfort and dryness ratings at each time point were compared between the two CL-LCP combinations using paired t test. Questionnaire data from days 2 to 6 were averaged before analysis. Ocular symptoms were compared using Wilcoxon signed rank test. Symptoms data for each subject were summarized as the highest severity of symptom from days 2 to 6 before analysis. Lens fit variables, such as tightness, lag, and movement were analyzed using a linear mixed model with subject random intercepts for differences in subject strata, CL-LCP combination, and their interaction. Subject strata–specific differences in CL-LCP combination were determined if the interaction was significant. The linear mixed model procedure allows all available data to be considered, thus, it was not necessary to exclude subjects for whom occasional entries were missing. A p < 0.05 was considered as statistically significant.
Study Population Characteristics
Of 37 subjects who enrolled, 35 (23 symptomatic and 12 nonsymptomatic) successfully completed the trial and were included in the analysis. Both subjects (one each from the symptomatic and nonsymptomatic groups) who discontinued from the trial cited difficulties in attending the clinic for the required visits.
Demographic data are detailed in Table 1. There was a significantly higher proportion of females in the symptomatic group compared with the nonsymptomatic group (p = 0.001) but no differences for any other demographic factor (p > 0.05).
Quality of Life Multidimensional Scale
Symptomatic subjects reported a significantly higher score for the frequency of visual and ocular symptoms subscale as compared with nonsymptomatic subjects (19.4 ± 3.4 vs. 16.3 ± 3.4, p = 0.013). There were no statistically significant differences (p > 0.05) between the symptomatic and nonsymptomatic groups for the tolerance of disturbing visual and ocular symptoms, cosmesis, personality traits, psychological traits, and satisfaction subscales of the QoLMS.
THQ Compliance and Completion Rates
Ninety-seven percent (n = 34) of subjects returned a completed set of THQ. One subject from the symptomatic group did not complete a THQ for an entire stage. Eighty-three percent (n = 29) of subjects were fully compliant with the THQ, that is, returned a complete set of THQ for both stages, with the actual date of completion matching the due date for each time point. Two subjects, both from the symptomatic group, completed a THQ on the wrong day but between days 2 to 6. Three subjects, two from the symptomatic group and one from the nonsymptomatic group, entered the incorrect date for completing at one time point on 1 day. All three instances seem to be typographical errors rather than noncompliance because the recorded date on the other two time points on the same day matched the due dates. All available data were used in the analysis.
Ocular Comfort and Ocular Dryness: NRS
Figs. 1 and 2 show the group mean comfort and dryness ratings reported during the study. Symptomatic subjects rated combination 1 as being significantly more comfortable than combination 2 on insertion (p < 0.05) and more comfortable and less dry after 8 hours of wear (p < 0.05). There were no significant differences (p > 0.05) between CL-LCP combinations for ocular comfort or ocular dryness at any time point in nonsymptomatic subjects.
The mean changes in comfort and dryness scores during the course of the wearing day are shown in Table 2, from which it can be seen that there were no significant differences (p > 0.05) in either factor for either symptomatic or nonsymptomatic subjects.
Frequency of Ocular Symptoms
As can be seen from Fig. 3, symptomatic subjects had a significantly lower frequency of ocular dryness (p < 0.001) and lens awareness (p < 0.001) when wearing combination 1 compared with combination 2. For nonsymptomatic subjects, there were no significant differences (p > 0.05) in frequency of any ocular symptom between the two CL-LCP combinations.
On average, galyfilcon A lenses showed significantly less primary gaze movement (0.16 ± 0.08 mm vs. 0.25 ± 0.17 mm, p < 0.001) and primary gaze lag (0.09 ± 0.08 mm vs. 0.25 ± 0.49 mm, p = 0.004) compared with balafilcon A lenses in both symptomatic and nonsymptomatic subjects.
Galyfilcon A lenses were significantly tighter on push-up than balafilcon A lenses in symptomatic subjects (52 ± 4% vs. 45 ± 7%, p < 0.001); however, there was no significant difference (p > 0.05) in nonsymptomatic subjects (50 ± 5% vs. 48 ± 6%, p > 0.05). The mean values for lens movement and tightness were within acceptable clinical parameters.
These results suggest that, in symptomatic CL wearers, the choice of CL-LCP combination can influence ocular comfort at insertion and end of day, ocular dryness at end of day, and the frequency of ocular symptoms during wear. On average, within this group, the magnitude of the comfort differential was at, or just above, the detection threshold for subjective responses of this type,27 and this indicates that roughly one-half of the symptomatic group could be expected to derive clinically useful benefits, in terms of comfort, from manipulations of their wearing system.
The THQ was critical in this study because it was used to determine the study outcomes. The choice of such a device might be criticized given that the reported compliance rates with paper diaries may be as low as 11%.28 However, efforts to promote compliance were incorporated as part of the study protocol as has been previously described. Data interrogation procedures were also implemented to monitor the correspondence between intended and actual THQ completion opportunities, whereas all subjects were experienced clinical trial participants who understood the importance of the THQ to the study and were familiar with completing questionnaires from previous trial participation. Although not infallible, these measures suggested that THQ completion was correctly achieved on 83% of available occasions. Nevertheless, the fact that a significant difference was found under these circumstances points to the indicated effect being substantial and therefore probably real.
The possibility that ocular symptoms can be reduced in some wearers is significant given the high proportion of discomfort-related discontinuation from CL wear, as previously discussed.2,4–7 Translating these findings to the real world must be done with caution. Subjects in this study were asked to wear systems that represented the extremes in our experience of CL-LCP system comfort responses, and in this way, we were able to maximize the subjective response to the change. In reality, the systems being used by most symptomatic wearers will fall somewhere between these limits, so the actual improvement gained might not be of the same magnitude. On the other hand, it should be remembered that the group of systems from which our test combinations were drawn represent the best of those available in the current market place, and it is more than likely that other CL-LCP combinations are in common use for which performance is worse than any of those previously discussed. For such situations, the prospect of improvement by changing systems may be more compelling.
Differences in subjective responses between CL-LCP combinations were not found in nonsymptomatic subjects. Although this intriguing result suggests that these robust individuals could “wear anything” and that this could be a true reflection of the behavior among such individuals, there are several other factors that must be taken into account.
First, it proved difficult to recruit nonsymptomatic wearers for this study. This was because of the strict inclusion criteria, limiting the potential pool of subjects and a general unwillingness to participate in this study in those who did meet the inclusion criteria. This resulted in a smaller sample for this group (n = 12) than the a priori calculated sample size (n = 24). Although the subsequent analysis will potentially have been underpowered, we note that the largest actual SD of paired comfort differences in the nonsymptomatic group was 1.1 compared with the estimate used in the sample size calculation of 1.5. Retrospective calculations made on this basis indicated that the sample of 12 subjects yielded a power of 81% to detect a mean difference of 1 point on a 1 to 10 scale, which was similar to the symptomatic group. Given that there were no missing data from the nonsymptomatic group, these retrospective calculations seem to be robust. Being mindful of the objections to retrospective assessments of this nature, we also observed that the magnitude of the differences between the two systems were substantially smaller for nonsymptomatic subjects, and this adds further weight to the likelihood that statistical significance would not have been reached for the behavior in this group. It should also be pointed out that the nonsymptomatic group would in reality not generally present themselves for rectification of a discomfort problem. By definition, they have no symptoms so would not be amenable to improvement by switching between combinations. Although their data are useful as a point of comparison, they are secondary to the symptomatic group. Thus, regardless of the smaller than calculated sample size in the nonsymptomatic group, the aim of this study was not affected.
Next, the choice of subject groupings might be problematic, given that those enrolled in this study were categorized as either symptomatic or nonsymptomatic based on the consistency of their comfort responses during previous clinical trials. This assignment of subjects to each group seems justified however because symptomatic subjects were found to report a significantly greater frequency of disturbing visual and ocular symptoms compared with nonsymptomatic subjects, as measured with the QoLMS at the commencement of the present investigation. The absence of significant differences for the other subscales on the QoLMS indicates a similarity between groups for personality traits, psychological characteristics, tolerance to disturbing visual and ocular symptoms, and satisfaction with their current optical correction before exposure to study products. This suggests that the variation in ocular comfort response between the groups is caused by other differences rather than preexisting psychological factors, such as personality traits and satisfaction with current optical correction.
It was also evident that the symptomatic group had a significantly larger proportion of females. However, the observed sex difference might be related to females being more likely than males to report dissatisfaction with CL wear3 and CL-related dry eye29 yet remain as CL wearers, whereas symptomatic males are more likely to discontinue.3 This suggests that males who remain in CL wear are more likely to be nonsymptomatic, whereas females are more likely to be symptomatic, as was observed in the present sample.
Finally, because the comfort scale is limited at its upper extremity, it may be that the responses of nonsymptomatic wearers were already close to this limit and therefore did not have the scope for significant further improvement. Comparing the distribution of comfort scores from both groups showed that, for nonsymptomatic wearers, 67% of responses were less than 9 when using the least performing combination, indicating that most of these subjects did have scope to improve their comfort score when using the other combination. The figure for the symptomatic group was 91%, which not only indicates a greater scope for improvement but also highlights differences between the two groups.
These arguments lend strength to the conclusion that the lack of significant difference between CL-LCP combinations in the nonsymptomatic group was a reflection of the true behavior in nonsymptomatic CL wearers. Perhaps this should not be surprising because these individuals are, by definition, already tolerant of their situation.
Although symptomatic subjects had a higher magnitude of change in ocular comfort and dryness across the day compared with nonsymptomatic subjects, the size of these comfort decrements was quite similar, and not statistically different, for the two CL-LCP combinations worn. This suggests that the mechanism responsible for increasing discomfort toward the end of the day was not affected by the particular CL-LCP combination used and tends to support the notion that end-of-day discomfort is driven by ocular, rather than lens-based, factors, in agreement with other recent studies.12,30,31 Various ocular structures might drive this response, including the lid wiper,32,33 conjunctiva,33 corneal epithelium,34 and tear film.35
Thus, although we have shown that comfort improvements can be gained by judicious choice of the CL-LCP combination, it seems that the classic decline in comfort toward the end of the day takes place regardless, albeit from a higher, or more comfortable, starting point. As the negative magnitude of this effect seems to be at least as great as the positive magnitude to be gained by optimizing the system being worn, it is clear that elimination of this persistent problem is also required to deliver a maximally comfortable result, and this will require further research.
It is possible that the greater discomfort of combination 2 was related to the three times higher incidence of solution-induced corneal staining (SICS) for combination 2 than for combination 1.36 Although some studies have reported no association between SICS and comfort,37,38 Diec et al.34 recently reported that CL wearers who experienced SICS rated their ocular comfort to be significantly lower than those who did not experience this phenomenon. However, the approach taken in this study was to choose combinations of CL-LCP based on the subjective responses of subjects in previous studies and not individual assessment of CL and LCP. It is therefore expected that individual factors impacting ocular comfort would have been taken into account by the final user of these products, the CL wearer. Our results indicate that, if the appropriate CL-LCP combination is prescribed, subjective responses can be modulated in symptomatic CL wearers.
In symptomatic CL wearers, ocular comfort and symptoms can be perceptibly improved by switching to alternative combinations of lens type and care system.
Comfort decrements occurring during the course of the wearing day are not eliminated, however. This finding provides justification for the continued efforts of both eye care practitioners and researchers to improve the comfort of CL wearers.
Brien Holden Vision Institute
Level 5 Rupert Myers Bldg North Wing
University of New South Wales
Sydney, New South Wales 2052
Received July 13, 2012; accepted February 15, 2013.
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