Features

05 May 2006

Effectiveness of lubricating daily disposable lenses with different additives

A new generation of daily disposable contact lenses has been developed to offer improved comfort to wearers. Stefan Schwarz and Joachim Nick describe a study of the comparative clinical performance of two of these lenses, Focus Dailies with AquaComfort and 1-Day Acuvue Moist

Since daily disposable soft lenses were first introduced in Europe in 1995, the simplicity, convenience and clinical benefits of the modality have proved popular with patients and practitioners alike. In 2005, nearly one in three new soft lens fits in the UK were daily disposables, although prescribing rates in other European countries varied widely. Industry data show that daily disposables accounted for more than half of the UK market value in 2005.

The advantages of this modality have been demonstrated in the literature over many years. Studies have shown that daily disposable lens wear offers greater convenience and patient satisfaction than other soft lens modalities. Compared with conventional daily wear, patients experience better comfort, improved vision, longer wearing times and fewer unscheduled visits when they replace their lenses every day and have fewer and less serious lens-related complications and symptoms.

Allergy sufferers have also been shown to experience fewer  symptoms and better comfort when wearing daily disposables than with re-usable lenses.

The introduction of progressive and toric daily disposable options has brought the benefits of these lenses to even more patients.
Yet despite this success, comfort has remained a significant issue with daily disposables, as it is with all lens types. Discomfort is the most common reason for patients giving up contact lenses and better comfort is the principal factor that would persuade lapsed wearers to try again.

Contact lens manufacturers have adopted a variety of strategies for improving comfort with daily disposable lenses, including the introduction of new lens designs and materials.

Practitioners have their own management strategies, such as recommending the use of rewetting drops or conditioning solutions to enhance the wettability of the lens surface, but these approaches have been shown to have serious limitations. Rewetting drops may temporarily ease discomfort, but, due to their short ocular residence time, do not provide sustained relief. Soaking in conditioning solutions may improve comfort and wettability in the short term but the effect tends to wear off during the day.

Over the past year, a new generation of daily disposable lenses has therefore emerged aimed at improving patient comfort. The approach with these lenses has been to utilise either polyvinyl alcohol (PVA) or povidone (PVP), used as primary ingredients in contact lens rewetting drops.
In 2005, there were two daily disposable contact lenses launched in the UK incorporating these ingredients. Focus Dailies with AquaComfort (also marketed in other parts of the world as Focus Dailies with AquaRelease and Focus Dailies Aqua) is manufactured by CIBA Vision from a newly formulated nelfilcon A material with PVA integral in the lens matrix.16 1-Day Acuvue Moist from Johnson & Johnson Vision Care is an etafilcon A lens, described by the manufacturer as containing PVP locked into the lens.19
The aim of this study was to compare the subjective and on-eye performance of 1-Day Acuvue Moist with that of Focus Dailies with AquaComfort.

Materials and Methods

This was a two-week, prospective, bilateral crossover, sponsor-masked study involving 266 subjects and 13 investigators (14 sites) in Germany. The study was conducted from November-December 2005.

Each investigator was instructed to enroll up to 20 soft lens wearers, including habitual Focus Dailies users, this being the lens used more often in Europe, and according to the available power range of the test lenses. Subjects were required to have a minimum wearing time of eight hours per day, three days per week. Any subject with pre-existing irritation, requiring ocular medication, or with evidence of a systemic or ocular abnormality was excluded from the study. All subjects signed a written informed consent form prior to participation.

Subjects made three visits to investigators: a baseline/dispensing visit, then a follow-up/crossover visit and a final visit, each after one week of lens wear. Each subject was randomly assigned to one of two treatment groups to use either the test product (1-Day Acuvue Moist) or the control product (Focus Dailies with AquaComfort) for one week, and was then crossed over to the other product for the second week. Intra-subject comparison of test and control products was selected as the most sensitive study design to detect small differences in subjective performance.

All lenses were packaged in their commercial blister-packs but the identity of the study sponsor was masked to the subject. 

Like the original Focus Dailies, Focus Dailies with AquaComfort is made from nelfilcon A, a PVA-based material. However, the new lens incorporates an additional five times more unbound PVA compared to the previous lens.

The additional unbound PVA also has a higher molecular weight than that used to manufacture the lens. 1-Day Acuvue Moist is made from etafilcon A and packaged in saline that includes up to 0.05 per cent PVP. PVP is also described as being locked into the lens.19 For the study, 1-Day Acuvue Moist was available in two base curves (8.5mm and 9.0mm) and was fitted according to the manufacturer's fitting guidelines. Focus Dailies with AquaComfort is available on one base curve and was also fitted according to the manufacturer's fitting guidelines.

At the baseline/dispensing visit, investigators carried out a slit-lamp examination, fitted the lenses, evaluated overall fit and centration (on five-point scales, from unacceptably loose to unacceptably tight, and from centered to severely decentered), and measured visual acuity (VA).

Subjects were then issued with lenses. No solutions were required but subjects were advised that sterile saline could be used for rinsing.
At the follow-up/crossover visit, data on slit-lamp findings, lens fit and VA were again collected. Subjects then completed a questionnaire where they recorded the subjective performance of the first lenses used on a scale of 1-10, where 1=poor and 10=excellent, for the following attributes: comfort (initial, during day, end of day and overall); quality of vision; and lens handling (on insertion and removal).

At the final visit, objective data were again recorded along with subjective performance for the second lenses used. In addition, subjects were asked to indicate their level of preference for either lens (on a five-point scale from 'strongly prefer pair one' to 'strongly prefer pair two') with respect to the following attributes: end of day comfort; full day of comfortable wear; crisp, clear vision; ease of insertion; ease of removal; and overall preference. For each lens, subjects also indicated their level of agreement (on a five-point scale from 'completely agree' to 'strongly disagree') with a range of statements relating to these and other attributes relating to comfort, handling and convenience.

The average number of days lenses were worn per week, the average daily wearing time and average daily hours of comfortable wear were recorded at each visit. Any unscheduled visits during the study were documented in the same way as scheduled visits and adverse events, as defined in the protocol, were reported immediately.

A p-value <0.05 was regarded as statistically significant for non-inferiority, superiority was demonstrated based on 95 per cent one-sided lower confidence limit.

Results

Of the 266 subjects enrolled in the study, all were dispensed lenses. Four subjects discontinued during the course of the study (one wearing the control lens, three wearing the test lens), and one further subject was lost to follow up. Of the discontinued subjects, two were due to discomfort, one due to an unacceptable fit and one due to the product being unavailable.

A total of 261 subjects therefore completed the study.

Subject demographics

Of the subjects enrolled, 71 per cent were female and the average age was 34 years (range 14 to 67 years). The mean horizontal and vertical corneal radii were 7.75mm (range 7.0 to 8.65mm) and 7.73mm (range 6.98 to 8.52mm) respectively.

Representative of the European market, a majority (63 per cent) were habitual Focus Dailies wearers and most (83 per cent) wore daily disposable lenses. On average, subjects wore their habitual lenses 5.2 days per week. The average daily wearing time with subjects' habitual lenses was 12.2 hours and average comfortable wearing time was 10.7 hours.

Slit-lamp findings, lens fit and VA

There was no significant difference in any slit-lamp finding between the test and control lenses or between baseline and subsequent visits. One non-significant adverse effect was recorded, but this was unrelated to the product.

Although 1-Day Acuvue Moist was available in two base curves, Focus Dailies with AquaComfort, with one available base curve, achieved more optimal fits and was more often optimally centred, both at dispensing and after one week of wear.

The average VA was approximately 6/6 at the dispensing and at the follow-up visits. There was no significant difference in VA between the two lens types.

Subjective performance 

Ratings for initial comfort, comfort during the day and overall comfort were all significantly higher (better) for Focus Dailies with AquaComfort than for 1-Day Acuvue Moist (95 per cent one-sided lower confidence limit).

Mean ratings at the follow-up visit (0-10 scale) were: 8.6±1.7 vs 8.0±2.3 for initial comfort; 8.2±1.8 vs 7.9±2.0 for comfort during the day; and 8.0±1.8 vs 7.6±2.1 for overall comfort, for Focus Dailies with AquaComfort and 1-Day Acuvue Moist respectively.

Mean ratings for comfort at the end of the day were 6.9±2.4 for Focus Dailies with AquaComfort and 6.5±2.6 for 1-Day Acuvue Moist, this difference demonstrates parity but was not statistically significant for superiority.

Subjective comfort ratings for Focus Dailies with AquaComfort (initial comfort, comfort during the day, comfort at the end of the day and overall comfort) were not lower than that of 1-Day Acuvue Moist lenses by more than half a grade (p<0.001).

Similarly, subjective ratings for quality of vision and handling on insertion (0-10 scale) were significantly higher (better) for Focus Dailies with AquaComfort compared to 1-Day Acuvue Moist (95 per cent one-sided lower confidence limit, Figure 4).

Mean ratings at the follow-up visit were: 8.8±1.5 vs 8.1±1.9 for quality of vision; and 8.8±1.5 vs 6.8±2.7 for handling on insertion, for Focus Dailies with AquaComfort and 1-Day Acuvue Moist respectively. There was parity, but no significant difference between the two lenses for handling on removal.

Preferences

Of those that expressed a preference, there was a statistically significant difference in favour of Focus Dailies with AquaComfort for overall preference (p=0.026), crisp, clear vision (p<0.001) and ease of insertion (p<0.001).

For overall preference, 57 per cent of subjects preferred Focus Dailies with AquaComfort compared to 43 per cent who preferred 1-Day Acuvue Moist. For crisp, clear vision, 67 per cent preferred Focus Dailies with AquaComfort and 33 per cent preferred 1-Day Acuvue Moist.

The most marked difference in preference was for ease of insertion, 84 per cent of subjects preferring Focus Dailies with AquaComfort compared to 16 per cent who preferred 1-Day Acuvue Moist.

Lens attributes

Focus Dailies with AquaComfort achieved a higher rate of agreement for all statements except for ease of removal. These statements included 'Lenses feel comfortable all day' and 'Lenses feel comfortable at the end of the day'. The most apparent advantages of the lens were for ease of insertion, providing crisp, clear vision, and convenience of use.

Ninety per cent of subjects agreed ('completely agreed' or 'somewhat agreed') with the statement 'Lenses are easy to insert' with Focus Dailies with AquaComfort, compared to 48 per cent with 1-Day Acuvue Moist.

Wearing times

Focus Dailies with AquaComfort were worn for more days per week, on average, than the 1-Day Acuvue Moist lenses (6.9 days vs 6.0 days). There were no significant differences in average daily wearing time or average daily hours of comfortable wear between the two lens types, or between subjects' habitual lenses and the study lenses.

Discussion

The objective of this study was to compare the subjective and on-eye performance of Focus Dailies with AquaComfort with that of 1-Day Acuvue Moist.

Subjects rated their initial comfort, comfort during the day, overall comfort, quality of vision, and handling on insertion as significantly better with Focus Dailies with AquaComfort than with 1-Day Acuvue Moist. They also preferred this lens overall, as well as for vision and ease of insertion.
Initial comfort and ease of insertion are particularly important lens attributes for patients new to contact lenses and are features likely to attract spectacle wearers to contact lenses and help them achieve a successful contact lens trial. Initial comfort is also an important attribute when upgrading existing and lapsed wearers to new lens types.

In addition to higher subjective ratings, Focus Dailies with AquaComfort also showed some advantages in fitting characteristics. The lenses achieved more optimal fits at dispensing and after one week of wear and more optimal centration with one base curve compared to 1-Day Acuvue Moist with two base curves available.

Many factors have been shown to influence soft lens comfort. Lens factors may relate to the inherent properties of a particular lens type or the quality of the lens fit.5 Some authors have found differences in initial comfort between lenses of varying water content.

A number of studies have suggested a correlation between subjective comfort and soft lens dehydration, while others have found no such relationship.

Among lens fit factors, increased lens movement and decentration may adversely affect soft lens comfort.

Edge thickness and profile might be expected to exert an influence, although variation in edge thickness of high water content lenses does not appear to have any effect.

In the present study, although other lens factors may well have played a role, the incorporation of different additives in the two lens types was expected to contribute to differences in comfort. The findings of a previous study, comparing the original Focus Dailies lens with Focus Dailies with AquaComfort, would seem to support this. This study found that subjects preferred the new lenses for overall comfort and end-of-day comfort although the base material, lens design and fitting characteristics were the same.

The two approaches to additives, while both designed to improve comfort, differ considerably. With Focus Dailies with AquaComfort, the gradual release of excess PVA from the lens is effected through the patent-pending AquaRelease moisturising agent.

Pressure on blinking 'squeezes' the lens, pumping PVA out of the lens and spreading it over the lens and into the tears. Unlike the rapid release that occurs with the instillation of rewetting drops, this mechanism releases small quantities with every blink throughout the day, producing a longer-lasting effect.

With 1-Day Acuvue, a different additive PVP is described by the manufacturer as being 'locked into' the etafilcon A matrix rather than being released from the polymer. In a recent study involving 44 subjects, of whom 41 completed the study, the authors reported improved comfort and reduced dryness with 1-Day Acuvue Moist when compared with Focus Dailies with AquaComfort.

In this smaller (n=41) study, subjective performance was recorded on a five-point descriptive scale, typically: excellent, very good, good, fair and poor, and results were presented as 'top two box' percentages.

Significant differences in favour of 1-Day Acuvue Moist were reported for some subjective responses but there was no significant difference between the two lens types for either comfort on insertion or ease of insertion.

The authors of the above report suggest that the permanence of PVP upon the etafilcon A matrix has superior subjective comfort benefits for the patient. However, this hypothesis is not supported by the present, large-scale study, which demonstrated clear differences in favour of Focus Dailies with AquaComfort.    

Conclusions

This study compared the effectiveness of two new lubricating daily disposable contact lenses that use different additives to improve patient comfort.

Focus Dailies with AquaComfort, in which PVA is used as an additive in the lens matrix and releases gradually, was found to be more effective than 1-Day Acuvue Moist, where the PVP additive is described as locked into the lens. Comfort, quality of vision and handling on insertion were all superior with Focus Dailies with AquaComfort. Patients preferred the lens to 1-Day Acuvue Moist for vision and ease of insertion, as well as for overall preference. Of the two lenses, Focus Dailies with AquaComfort also showed better fitting characteristics.

These findings suggest that Focus Dailies with AquaComfort is the daily disposable lens of choice for comfort for all wearers and especially for new patients and spectacle wearers.

Acknowledgements

The authors would like to thank the investigators who took part in this study, which will be presented as a poster at this year's BCLA Clinical Conference.

References
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Optometrist Stefan Schwarz owns a private practice in Hildesheim, Germany and Joachim Nick is an optometrist at CIBA Vision, Global Clinical Affairs


 

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