Daily Disposable Contact Lenses: The King in Waiting?
BY ERIC PAPAS, PHD, MCOPTOM, DIPCL, FAAO
As a contact lens modality, daily disposability has considerable appeal, mainly due to its promise of release from the tedious routine of lens cleaning, disinfection, and storage. It is striking, therefore, that the allure of this particular modality has been easier for some patients and practitioners to resist compared to others, as is apparent from the wide variation in uptake rates around the world. For example, in the years between 2007 and 2011, around 50 percent of soft lens fits in Denmark and 40 percent in the United Kingdom and Japan were with daily disposable contact lenses, while this figure was much smaller in the United States and Canada at about 14 percent (Efron et al, 2012).
Why should such discrepancies exist? For any individual practitioner, the decision of which lens type to fit begins with the clinical picture presented by each wearer, but it is then influenced by a range of additional factors. One implication of the usage data is that many practitioners appear to remain unconvinced that these non-clinical aspects of care delivery, including cost, are outweighed by the perceived clinical advantages.
As daily disposable lenses have been around for some time now, we should expect to be able to look to the available evidence base to give direction.
Reduced Infiltrative Events
The most recently published work in this field relates to the issue of inflammatory complications and indicates the potential value of disposability in protecting against corneal infiltrative events (Chalmers et al, 2012). By using a case control study design, in which each individual who has a particular condition is matched with several others who do not, the relative risk of suffering that condition can be calculated for a range of likely risk factors. Taking this approach indicated that the chance of having a corneal infiltrative event (which was defined in this study as microbial keratitis, contact lens peripheral ulcer [CLPU], contact lens-associated red eye, infiltrative keratitis, asymptomatic infiltrative keratitis [AIK], superior epithelial arcuate lesions [SEALs], or solution hypersensitivity) while wearing re-usable daily wear lenses was 12.5 times greater than it was for those in a daily disposable modality. On the face of it, this seems to be a huge advantage.
However, as the study authors point out, the sample of daily disposable users on which the numbers are based was relatively small, which has the consequence that the confidence limits around the risk estimate become rather broad. The actual range stretched from 1.5x to 100x, and if the true risk turned out to be toward the lower figure, this might be perceived as of limited clinical value. Although such extreme pessimism is probably unjustified, there remains a need for additional data to confirm the upside potential.
Daily Disposability Versus Extended Wear
While disposability’s most obvious application is in daily wear, it seems that the modality may have something to tell us about the closed-eye situation as well. The association of extended wear with an increased complication rate is well known, and several studies have highlighted the risks of sleeping while wearing contact lenses (Dart et al, 2008; Edwards et al, 2009; Stapleton et al, 2008). The results of one new study suggest that daily lens exchanges may reduce some of these complications, however (Ozkan et al, 2012). Comparing extended wearers who replaced their lenses on a monthly schedule with those who did so every morning after awakening, the latter group showed fewer adverse events. Particularly noticeable was the fall in the amount of episodes categorized as having a “mechanical” etiology. Thus, the number of subjects experiencing SEALs, contact lens-induced palpebral conjunctivitis, and corneal erosions decreased from 5 percent of the sample to about 1 percent.
Equally interesting was the observation that moving the time of replacement from the morning to before sleeping increased the frequency of events such as CLPU and AIK. These divergent behaviors may help us understand the mechanisms underlying some of the problems traditionally associated with extended wear. Mechanical complications, for example, are not generally thought to have a microbiological cause, and so the regular removal of accumulated debris or tearborne toxins may be an important etiological factor controlling their appearance. On the other hand, for those events in which microbes do seem to be implicated, the suggestion is that handling prior to sleep is undesirable, presumably because it provides a vector for contamination.
Daily Disposability and Microbial Keratitis
The duration of this extended wear study was one month, which, unfortunately, was not long enough to establish how those complications that occur less frequently but are more serious would behave under such conditions. Most worrying of these problems is, of course, microbial keratitis (MK), and the question of how disposability affects a wearer’s chance of developing this devastating infection has been keenly discussed for some time. To the surprise of many, the first data to be published on this subject indicated that daily wear MK rates were actually slightly higher (about 1.5x), with one-day disposable than with less regularly replaced soft lenses (Dart et al, 2008; Stapleton et al, 2008). Reasons that were proposed for this excess included the possibility of ocular surface damage caused by handling difficulties with this type of lens and the presence in the sample of certain brands that appeared to be particularly problematic; it is also quite possible that these two factors were interlinked. Perhaps as a result of changes to the range of available product over the years since this work was published, more recent interpretation of the data has suggested that the absolute risk of infection for daily disposables is at a similar level to that of other soft, daily wear lenses (Stapleton and Carnt, 2012). Digging a little deeper, however, shows that disposability may offer benefits in terms of disease severity. The rate at which daily disposable wearers experience severe or moderate keratitis is 0.5 events per 10,000 wearers per year, which is roughly half of what occurs with traditional daily wear. Further, the risk of vision loss as a result of these events is low. Thus, even though a daily disposable wearer may have the same general probability of affliction by MK as other soft lens users, they can expect to undergo a milder level of disease and have fewer subsequent visual consequences if they are unlucky enough to be so affected.
The Bottom Line
The balance of evidence from these recent studies supports the idea that daily disposability provides a clinical option with fewer complications. Of course, wearers still need to comply with the instructions of their practitioner on issues such as replacement frequency and avoiding napping while wearing lenses, but that’s another story. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #206.
Associate Professor Papas is executive director of Research & Development, Brien Holden Vision Institute and Vision Cooperative Research Centre, and senior visiting fellow, School of Optometry & Vision Science, University of New South Wales, Sydney, Australia. The Brien Holden Vision Institute and Vision Cooperative Research Centre have received research funds from B+L, AMO, and Allergan and have proprietary interest in products from Alcon, CooperVision, and Carl Zeiss. You can reach him at firstname.lastname@example.org.
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