Daily Disposables for the 21st Century
A look at expanded offerings and new uses in the daily disposable market from 2000 to 2015.
By Stephanie M. Cox, OD, FAAO, & Jason J. Nichols, OD, MPH, PhD, FAAO
Daily disposable contact lenses have been the fastest growing contact lens modality for the last few years (Nichols, 2015). Based on this survey of more than 500 practitioners in the United States, it can be estimated that approximately 23% of contact lens fits/refits were with daily disposable lenses in 2014. This number was estimated as 20% in 2013. In addition, most eyecare practitioners report that they expect to prescribe even more silicone hydrogel (SiHy) daily disposables in 2015 (Nichols, 2015).
A similar survey found that the most common treatment for contact lens dry eye was refitting patients into a lens that is replaced more frequently, with daily disposables being reported as the most effective lens to reduce contact lens dryness or discomfort (Ablamowicz and Nichols, 2014).
Contact lens manufacturers have continued to expand the options available in the daily disposable modality over the years. With the addition of new lenses, it is important to continue to educate our patients about this modality and to utilize these lenses to the best of our ability. This article aims to review the expansions in the daily disposable modality since 2000 and to review the literature surrounding several of these expansions.
Reviewing the Advantages of Daily Disposables
Since the introduction of daily disposables in the mid-1990s, the reduction in lens deposition and contact lens-related complications has been well documented (Chalmers et al, 2015; Lazon de la Jara et al, 2013; Nason et al, 1994, Nilsson and Söderqvist, 1995).
In addition to improved health with high-frequency replacement contact lenses, several studies have documented an improvement in comfort with frequent replacement contact lenses compared to conventional lenses (Lazon de la Jara et al, 2013; Hickson-Curran et al, 2014; Nason et al, 1994; Nilsson and Söderqvist, 1995). Daily disposables have the most frequent replacement schedule; therefore, it is natural to conclude that this modality would be associated with good comfort. The impact of daily disposable lenses on comfort may be greatest when considering contact lens wearers who experience lens discomfort. One study showed that some contact lens wearers who had lens discomfort problems experienced better comfort when refit into a daily disposable lens (Hickson-Curran et al, 2014). Because the most common reason for contact lens discontinuation is discomfort (Richdale et al, 2007), refitting into a daily disposable lens at the first sign of discomfort may help to prevent discontinuation of contact lens wear.
One additional advantage of daily disposables is the ease of care provided to patients. Many eyecare professionals were hopeful that this lens modality would put an end to noncompliance and the complications that can result from it. However, studies show that even some daily disposable contact lens wearers are not compliant with replacement regimens (Chalmers et al, 2015; Dumbleton et al, 2013). Therefore, it is important to continue to emphasize compliance in all lens wearers, including daily disposable wearers.
The first daily wear SiHy contact lens was introduced in the 1990s; however, the first daily disposable lens manufactured in a SiHy material was not introduced in the United States until approximately 10 years later. The introduction of a new contact lens material initiated questions about impact on patient comfort and ocular health with the new lenses.
One major advantage of SiHy lenses is their increased oxygen transmissibility compared to hydrogels. A contact lens’ oxygen transmissibility is critical to corneal health. Off- and on-eye studies have shown that SiHy materials provide better transmissibility of oxygen compared to hydrogel materials (Bonanno et al, 2009; Filipecki et al, 2014). It was speculated that patients would experience better comfort with a contact lens with increased oxygen permeability (Guillon, 2013). However, the impact on contact lens comfort in daily wear lenses due to oxygen transmissibility has fallen short of what some had originally anticipated (Guillon, 2013).
Most clinicians welcomed the addition of silicone to contact lenses from an oxygen transmissibility perspective, but some questioned whether it could reduce wettability due to its hydrophobicity. This reduced wettability might negatively impact comfort. Over the course of the past 15 years, we have seen a few generations of SiHy materials designed to overcome these concerns.
The first generation used surface treatments to mask the hydrophobicity of the lens and to maintain the wettability of the lens surface. A second generation of SiHy lenses added a hydrophilic group to the hydrophobic molecule. Finally, a third generation uses new long-chain, silicone-based macromers instead of the original hydrophobic molecule (Szczotka-Flynn, 2008; Chou, 2008).
Clinical studies have aimed to answer whether silicone hydrogels or hydrogels provide better comfort. One study involving SiHy daily disposable contact lenses showed that contact lens comfort has not been compromised due to the introduction of SiHy materials (Varikooty et al, 2015).
In a review article, Guillon (2013) summarized more than 10 studies in detail, with some showing increased comfort with SiHy lenses compared to hydrogel lenses, and others finding no difference. He concluded that comfort is dependent on more than lens material.
The Tear Film and Ocular Surface Society (TFOS) International Workshop on Contact Lens Discomfort (CLD) report stated, “…in contact lens wearers who exhibit unacceptable comfort, making changes to the lens material, design, care system, and replacement schedule can improve comfort” (Jones et al, 2013). This statement emphasizes that many factors can influence contact lens comfort, not only the material.
Spherical to Toric to Multifocal
The first toric daily disposable contact lens was introduced in the United States approximately 15 years after the launch of daily disposables. Studies have shown that even patients who have low amounts of astigmatism have better vision objectively and subjectively with toric contact lenses (Cho et al, 2012; Sulley et al, 2013). In addition, comfort was statistically equivalent between the toric and spherical contact lenses (Cho, et al, 2012).
A major reason for the lack of expansion of the toric market could be cost. Since 2000, the prescribing of toric contact lenses has increased in most countries (Morgan et al, 2013). However, the percent of toric lenses prescribed in the daily disposable modality is significantly lower (studies report 9% and 12%) compared to that of torics prescribed for daily wear (studies report 23% and 29%) (Efron et al, 2013; Efron et al, 2011).
When disinfecting solutions are taken into account, toric daily disposable lenses are more expensive compared to monthly replacement lenses if worn four or more days per week (Efron et al, 2010) (Figure 1). This contrasts with the cost of spherical and multifocal daily disposable contact lenses, which are more expensive than their monthly counterparts (when including cost of care solutions) only if worn six or more days per week (Efron et al, 2010). The income of countries as assessed with gross domestic product at purchasing power parity per capita is correlated weakly, but significantly, with the percent of toric lenses prescribed (Efron et al, 2011) and strongly with the percent of daily disposables prescribed (Efron et al, 2013). These correlations support that cost may have a large impact on purchasing, especially within the daily disposable market.
Figure 1. The cost per wear of A) spherical, B) toric, and C) multifocal contact lenses when worn various days per week. The values calculated for daily, two-week, and monthly replacement lenses assume compliance with care and replacement schedules and include cost of care solutions, contact lenses, and professional services (Efron et al, 2010). Reprinted by permission of John Wiley & Sons, Inc.
The first multifocal daily disposable contact lens was introduced to the United States a short time after toric daily disposables. Multifocal daily disposable contact lenses appear to be prescribed less commonly than other modalities (Morgan et al, 2011), but this could be due to their more recent appearance in the United States. Multifocal daily disposable contact lenses are often used when fitting presbyopes, but another potential use for these lenses is for myopia control in children.
Literature suggesting that peripheral myopic defocus could help to slow myopia progression is consistently increasing (Walline et al, 2013; Smith, 2013); this can be achieved with a center-distance multifocal contact lens. Along with the optics necessary for myopia control, we must also consider the safety of contact lenses for children. Daily disposable contact lenses are the safest contact lens modality for children (Chalmers et al, 2011).
Currently, only one center-distance design is commercially available in the daily disposable modality within the United States. Daily disposable lenses for myopia control are being introduced in markets outside of the United States. Therefore, we should watch for introductions within the United States and/or begin considering daily disposable center-distance multifocal contact lenses for younger patients.
Incorporation of Wetting Agents
Some manufacturers incorporate a wetting agent into their daily disposable contact lenses in an effort to improve comfort. These wetting agents include polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP). They are released from the lens during wear. Hydroxypropylmethylcellulose (HPMC) and polyethylene glycol (PEG) have also been incorporated with PVA to enhance the lens’ ability to provide patient comfort.
In one study, subjects ranked end-of-day comfort, strength of lens recommendation, and overall rating similarly for a PVA-releasing lens and a different lens that did not include a wetting agent (Peterson et al, 2006). However, when forced to compare the two lenses, subjects reported a preference for the PVA-releasing lens when considering initial comfort, end-of-day comfort, visual acuity, and overall comfort (Peterson et al, 2006). Another study showed that the pre-lens tear film breakup time improved with the incorporation of HPMC and PEG to the PVA-releasing lens (Wolffsohn et al, 2010). Lenses with PVP reduced dryness symptoms in symptomatic patients compared to the same lenses without PVP. PVP-containing lenses also significantly reduced higher-order aberrations and resulted in fewer changes in the aberrations between blinks (Koh et al, 2008).
These studies show the potential advantages of incorporating wetting agents into daily disposable contact lenses. However, it is important to keep in mind that many other factors may impact lens comfort.
Looking to the Future
While not currently available in the United States, studies have found that drug delivery using contact lenses is possible. The use of a daily disposable lens for drug delivery has many applications. Chronic conditions (such as glaucoma) may be better served with continuous wear contact lenses that utilize extended release technologies; acute conditions (such as bacterial infections and some inflammatory conditions) may be better served with shorter-term treatment options. One example for daily disposables in drug delivery would be its use in postsurgical patients. The lens could be removed at the one-day post-operative appointment. At that time, the necessary drops could be dispensed or a new contact lens could be applied.
The first method of drug delivery includes soaking currently available hydrogel and SiHy lenses in various drug-containing solutions (Tashakori-Sabzevar and Mohajeri, 2014; Morrison and Khutoryanskiy, 2014). One of the problems encountered with this method is a quick release of the drug from the contact lens, which does not provide the extended release that the contact lens is hoped to achieve.
Some drug delivery control was attained by soaking the contact lenses in a solution that slows diffusion of the drug from the contact lens, either prior to, or concurrently with, the drug of interest. This additional diffusion barrier slowed the release of the drug from the contact lens from 80% of the drug in 30 minutes to 75% in 12 hours (Carvalho et al, 2015).
A recent study showed that when daily disposable lenses were soaked in a solution containing antibiotics and placed into a model eye system, the release of the drug was more constant throughout the 24-hour test period compared to release while in a solution-containing vial (Bajgrowicz et al, 2015). The difference in release characteristics between an in vitro system and a model system suggests that in vivo studies are needed to fully understand this application of daily disposable contact lenses. That said, this method of drug delivery is promising for the future.
A newer technology being utilized for drug delivery is called molecular imprinting (Figure 2). This technology allows for better control of drug delivery. In short, specialized functional monomers are incorporated into the contact lens. These functional monomers form binding sites for the drug. The binding sites’ affinity for the drug, number of monomers, and stability of the binding site account for the extended release of the drug from the contact lens (Carvalho et al, 2015). However, with this method of drug delivery, factors important in clinical use, such as lens flexibility, modulus, and optical clarity, must be overcome (Carvalho et al, 2015; Morrison and Khutoryanskiy, 2014).
Figure 2. An illustration showing the process of molecular imprinting. Adapted from Tashakori-Sabzevar and Mohajeri, 2014.
Studies have shown some success with this technology using nonsteroidal anti-inflammatory drugs (NSAIDs) and antibiotics. The use of diclofenac sodium-imprinted lenses has demonstrated very consistent flow rates for up to two days (Tieppo et al, 2012). An antibiotic-imprinted contact lens demonstrated good release of the drug for several days while maintaining transmissibility necessary for good vision, low amount of refractive change, adequate wettability, and good modulus (Hui et al, 2014). Given the short time span necessary for most antibiotics, a daily disposable modality may be best for this type of drug delivery.
The final technology for contact lens drug delivery involves nanotechnology. The nano-sized systems are incorporated into the contact lens during production (Carvalho et al, 2015). This particular modality of drug release could be more applicable for use in chronic conditions because it has the ability for extended drug delivery time. In addition, this technology is not limited by the size or structure of the drug, unlike some of the other drug delivery methods mentioned previously (Carvalho et al, 2015). While promising, extensive studies are necessary to employ this technology clinically in the future.
In addition to drug delivery, contact lenses are being considered for their potential role in diagnostics. These diagnostic devices may or may not be suitable for daily disposables, so we will not discuss them in great detail within this article. However, the diagnostic parameters being considered include monitoring intraocular pressure based on changes in the corneal curvature or sensing changes in blood glucose or antibody concentration within the tears (Farandos et al, 2014). Due to their sensitivity, the sensors can degenerate with time. This degeneration could make the incorporation of diagnostic sensors into daily disposable lenses a possible application.
Daily disposables are a great option for most patients to wear each day, especially children, patients who have excessive contact lens deposition, and noncompliant patients. However, it is important to consider all of the potential uses for daily disposable lenses.
Daily disposables are an obvious choice for patients who wish to wear contact lenses on only a part-time basis (e.g., sports). This prevents contamination from a lens that has been sitting in the same solution for several days or weeks.
However, it is also important to consider these lenses in situations in which they can be used in addition to a monthly or two-week contact lens. For example, some patients may benefit from using daily disposables when traveling because bulky bottles of care solution do not have to be packed in their luggage. There are even options of colored daily disposables for cosmetic enhancement, which may also be useful if patients only want to wear the colored lenses for special occasions.
As daily disposable contact lenses continue to improve and more options become available, it is important for eyecare practitioners to consistently consider this modality for patients. CLS
For references, please visit www.clspectrum.com/references and click on document #235.
Dr. Cox is a clinical assistant professor at the University of Alabama at Birmingham School of Optometry and is pursuing a PhD in Vision Science. She has received a travel grant sponsored by The Vision Care Institute.
Dr. Nichols is an assistant vice president for industry research development and professor at the University of Alabama-Birmingham as well as editor-in-chief of Contact Lens Spectrum and editor of the weekly email newsletter Contact Lenses Today. He has received research funding or honoraria from Vistakon, Alcon, and Allergan.