DAILY DISPOSABLE LENSES
A Look at Daily Disposables
Are daily disposable lenses poised for global domination, or are they another cog in the wheel?
By Maria Markoulli, PhD, MOptom, GradCertOcTher, FBCLA, FAAO
In days gone by, patients would be prescribed and would wear their conventional soft contact lenses for a year or more, needing to use separate solutions for cleaning, rinsing, disinfecting, soaking, and enzyme removal. The combination of these contact lenses—first introduced in the 1970s—and the care system was onerous for patients, resulting in confusion and noncompliance (Collins and Carney, 1986). More importantly, the longevity of the contact lens use placed patients at significant risk of adverse events when compared to more frequent replacement contact lenses (Boswall et al, 1993).
Daily Versus Extended Wear
Conventional lenses have been largely superseded by regular replacement hydrogel lenses, and the numerous care solutions have been replaced with single multipurpose solutions. The regular replacement of contact lenses on a monthly or two-weekly daily wear basis reduced the inconvenience and cost associated with losing a contact lens. Negative reactions such as solution-related adverse events (Carnt et al, 2007) and hypoxia-associated issues persisted (Chan and Weissman, 1996). Issues relating to chronic contact lens wear, such as contact lens papillary conjunctivitis (Donshik and Porazinski, 2000), and inflammatory conditions, such as inflammatory keratitis (Holden et al, 1999), also persisted.
Additionally, noncompliance continued to be an issue, including unscheduled overnight wear (Dumbleton et al, 2013) and prolonged use of contact lenses; some patients wore their lenses longer than the prescribed two-week or one-month period (Collier, 2012).
To address the Holden-Mertz criterion (Holden and Mertz, 1984) and the issue of hypoxia, high-oxygen-transmissible contact lenses in silicone hydrogel (SiHy) material were introduced in 2001, giving patients the convenience of overnight wear. The idea here was that these contact lenses would be worn for 29 nights/30 days continuously, known as the continuous wear modality. These contact lenses reduced the incidence of striae and folds in the stroma (Covey et al, 2001) as well as neovascularization, both hallmarks of hypoxia (Dumbleton, 2002).
Despite this increase in oxygen transmissibility, the most serious of adverse events—microbial keratitis—continued, and it continues to remain a concern when contact lenses are worn overnight. Other concerns include mechanical events, such as superior epithelial arcuate lesions and localized contact lens papillary conjunctivitis (Dumbleton, 2003). Inflammatory events, such as infiltrative keratitis, also continue to occur in SiHy lenses up to two times more than when compared to low-Dk hydrogel lenses (Szczotka-Flynn and Diaz, 2007).
In light of the adverse events associated with extended wear (Dumbleton, 2002), this modality remains the least common. In daily wear, however, SiHy lenses are the material of choice, forming approximately 73% of all new lens fits (Efron et al, 2015), mostly in the daily wear schedule.
In the 1990s, the first daily disposable (DD) lenses were produced (Meyler and Ruston, 2006), eliminating the need for care products and introducing convenience and flexibility into the wear schedule. In addition to providing convenience, DDs have eliminated solution-related events and minimized contact lens papillary conjunctivitis-related events (Morgan et al, 2013) by virtue of frequent replacement and, hence, minimal protein, lipid, and calcium deposition.
Given this brief history of contact lens wear modalities, a few obvious questions are: are DDs here to stay, and are they the way to go for clinicians and patients alike? Or, are they just another cog in the wheel of contact lens development?
Here to Stay?
A survey capturing the extent of DD contact lens prescribing worldwide in 40 countries by Efron et al (2015) strongly indicated that DD lenses are working their way to global domination. According to that survey, DDs represented 27.1% of all soft lens fits in 2014 as compared to 5.3% in 2002. Manufacturers are responding to this trend, with the production of SiHy DDs with the addition of lubricants into their packaging solution and the inclusion of additional parameters. But from where does this trend originate?
Convenience One of the most important factors driving this trend is that of convenience. Convenience also drives compliance. With fewer components involved in the care of these contact lenses and their cases, it is easier for patients to fit these lenses into their lifestyle.
This is the ideal modality for patients who only want to wear their lenses on weekends or just for occasional sporting events, for example. It is also more cost effective for this patient group (Efron et al, 2012). Cost, however, increases once lenses are worn more than four times per week (Efron et al, 2012). DDs can also increase convenience for frequent travelers or for neophytes who are undecided about contact lens wear.
Contact Lens Case Hygiene Another issue avoided by DD contact lens wear is that of poor contact lens case hygiene. Poor lens hygiene has been associated with microbial keratitis (Stapleton et al, 2007; Wiley et al, 2012) and contamination with gram negative bacteria (Tilia et al, 2014); disease severity has been shown to correlate with an increase in the range of bacterial types found in the case (Wiley et al, 2012). Case contamination has been found in 18% to 85% of cases (Wu et al, 2015), depending on the study location, study design, microbiological sampling, and methods. Lakkis et al (2009) reported that this contamination can occur quite early on, even within two weeks of using the lens case. The use of DDs eliminates the use of contact lens cases and, therefore, reduces the risk of noncompliance and infection relating to poor habits.
Adverse Events For clinicians, these benefits go hand-in-hand with the reduced risk of adverse events (Suchecki et al, 2000). Microbial keratitis is the most significant complication relating to contact lens wear. This has been estimated to occur in 1.9 (confidence interval, 1.8 to 2.0) per 10,000 wearers of soft contact lenses worn on a daily wear schedule and used in conjunction with lens care products (Stapleton et al, 2008). When overnight wear is introduced, this incidence rises to 25.4 (confidence interval, 21.2 to 31.5) per 10,000 wearers of soft extended wear lenses (Stapleton et al, 2008).
Interestingly, when the risk factors of overnight wear, contact lens disinfection noncompliance, and contaminated contact lens cases are eliminated with DDs, there is no change in the incidence of microbial keratitis compared to daily wear; this is estimated to occur in 2.0 (confidence interval, 1.7 to 2.4) per 10,000 wearers (Stapleton et al, 2010). In an abstract presented at the 2010 ARVO meeting, those authors reported that the risk of microbial keratitis in DDs varied with contact lens type, the material properties, and design. This finding was also reported by others (Dart et al, 2008; Chalmers and Gleason, 2013). This indicates that more research and development in this field could further reduce the risk.
Wear of contact lenses on a DD schedule has, however, been associated with the lowest risk of severe microbial keratitis of all contact lens wear modalities (Stapleton et al, 2008). Potentially, this is due to eliminating the need for a contact lens case and, hence, minimizing the possibility of gram-negative contamination.
To assess the risk of adverse events relative to no contact lens wear, Sankaridurg and colleagues (2003) randomized 281 myopes to either DD contact lenses or spectacles for a 12-month period. With the contact lens group, the type and incidence of significant events per 100 eyes per year of lens wear were corneal peripheral ulcer, 2.5 events; infiltrative keratitis, 1.5 events; and papillary conjunctivitis, 1 event. No significant events were seen in the spectacle wearing group.
This small number of significant events in the DD group was deemed as “promising” by this research group. When the incidence of corneal erosions is compared between DDs and other wear modalities, DDs have the lowest risk (Willcox et al, 2010). Additionally, DDs showed the lowest risk for both corneal erosion and gram-negative contamination (Willcox et al, 2010), which are factors thought to predispose an individual to microbial keratitis.
Contact Lens Deposition More frequent replacement of contact lenses is associated with less deposition (Ilhan et al, 1998). This appears to translate to the incidence of contact lens papillary conjunctivitis (CLPC), which is thought to be a result of an immunological response. In his doctoral thesis, Skotnitsky (2007) found that 45% of wearers developed CLPC in SiHy extended wear. When these patients were refitted with the same lens but on a DD schedule, this resolved.
When SiHy DD contact lenses are compared to conventional hydrogel contact lenses in vitro, there is a significantly greater cholesterol deposition onto the new SiHy material (Walther et al, 2015), suggesting that patients who have greater lipid levels in their tear film may be more prone to deposits if fitted with a SiHy material.
By addressing the issue of deposits, DD lenses can also address the issue of vision; increasing deposition is directly related to a deterioration in vision (Gellatly et al, 1988).
Comfort An area that has been equivocal is the impact of DD contact lenses on comfort. Despite the advances in contact lens technology, contact lens uptake in the market, as a whole, has been stagnant; the number of contact lens wearers worldwide has not changed (Nichols et al, 2013).
A large factor associated with this is that the number of new wearers each year appears to equate to the number of people who drop out of lens wear due to comfort issues. In fact, the 2013 Tear Film and Ocular Surface Society (TFOS) workshop on Contact Lens Discomfort addressed the plateau of contact lens wearers, in which the number of patients dropping out of contact lens wear closely approaches that of new wearers.
While some have suggested that patients who struggle in other modalities are more successful once they are fitted with DDs (Hickson-Curran et al, 2014; Young et al, 2002), other studies indicate that comfort depends on the contact lens material and specific design worn (Diec et al, 2012).
What Comes Next?
Improving comfort, convenience, and safety is critical to the growth of the contact lens market as a whole. DDs have combatted many of the issues surrounding contact lens wear, and manufacturers have been listening, producing these in spherical, toric, and multifocal designs and, more recently, in SiHy materials. To increase comfort and lubricity, one company has increased water content from 33 percent in the SiHy core to more than 80 percent in the grafted hydrogel surface layer (Pruitt and Bauman, 2013).
The future may also see DD lenses with antimicrobial surfaces to further combat infectious and inflammatory events. And, with an increased focus on myopia control (Sankaridurg et al, 2011), we may see DDs fitted in young children for the purpose of preventing myopia progression.
Convenience has underpinned the development of the contact lens market. The prescribing trends indicate that DD contact lenses are headed toward global domination. For clinicians, this means embracing DDs in practice and ensuring that patients comply with this modality. For contact lens manufacturers, this means improving this product with lubricants, designs, and increasing the parameters available.
Efron et al (2012) predict that by 2020, DD contact lenses will make up 80% of the market. Given the current trend, not to mention the convenience and safety afforded by this lens wear modality, DD lenses are here to stay. CLS
For references, please visit www.clspectrum.com/references and click on document #243.
Dr. Markoulli is a lecturer at the School of Optometry & Vision Science at the University of New South Wales in Sydney.