The Role of Lens Care Solutions in Contact Lens Comfort
For comfortable lens wear, consider all of the factors that come into play, including care solutions.
By Heiko Pult, PhD, MSc, FAAO, FBCLA, FEAAO
|Dr. Pult is CEO of Horst Riede GmbH in Weinheim, Germany. He is involved in contact lens and anterior eye research at Cardiff University in the United Kingdom. He is a lecturer and independent investigator for several research groups, companies and schools. He has received research funding from Laboratoires Thea Pharma, France and Optima-Pharma, Germany; has received lecture and authorship honoraria from Johnson & Johnson, Germany and UK; and was a consultant for BON, Germany.|
Despite the skill and expertise of contact lens practitioners, contact lenses can become uncomfortable for patients; as we know, discomfort is the No. 1 reason why patients stop wearing their lenses (Rumpakis, 2010; Richdale et al, 2007; Pritchard, 2001). According to one study, about half of the patients who drop out of contact lens wear in the United Kingdom and three-fourths of those who drop out in the United States do so because of discomfort (Pritchard, 2001). Another study found that 12 percent of new contact lens wearers stopped wearing their lenses within five years because of discomfort, dryness, and red eyes (Pritchard et al, 1999).
Discomfort and dryness are key contributors to decreased wearing times and contact lens dropout, and about 50 percent of contact lens wearers report experiencing dry eye symptoms at least occasionally (Nichols and Sinnott, 2006). Lens materials and surface characteristics, as well as surfactant use and environmental factors, can affect lens deposition, and deposits can decrease the pre-lens breakup time, leading to symptoms of dryness (Sindt and Longmuir, 2007).
The better we understand why contact lenses become uncomfortable, the better we can proactively address these factors. This article will discuss what can cause contact lenses to become uncomfortable and how the appropriate care solutions can help improve the lens-wearing experience for patients.
Mechanism of Deposition
Deposits may come from the tears (Figure 1), the environment, or even from handling of the contact lens. Deposition of proteins, lipids, and mucins occurs relatively quickly after lens application. The tear film is a complex structure composed of water, salts, enzymes, proteins, immunoglobulins, lipids, metabolites, and exfoliated epithelial and polymorphonuclear cells (Rolando and Zierhut, 2001). When contact lenses dehydrate, the internal hydrophobic regions of tear proteins, including albumin, lactoferrin, and lysozyme, bind to the hydrophobic regions of the material. These proteins become denatured, which can cause immunological responses (Michaud and Giasson, 2001; Senchyna et al, 2004) and contact lens complications such as giant papillary conjunctivitis and inflammation, both of which are associated with symptoms of dry eye (Sindt and Longmuir, 2007). The water content and surface charge (ionicity) of a lens influence the rate of deposit absorption and adsorption (Sindt and Longmuir, 2007).
Figure 1. Tear film smear on a fresh silicone hydrogel lens 20 minutes after application caused by too rapid pre-lens tear film breakup.
Increased lysozyme deposition has been measured on traditional hydrogel materials, particularly those in FDA Group 4 (Carney et al, 2009) (Figure 2). Hydroxyethyl methacrylate/glycerol methacrylate (HEMA/GMA) contact lenses absorb the least amount of protein of the polyHEMA lenses, suggesting that carboxymethylation, which increases the negative charge, is a more significant factor than is high water content in protein spoliation (Maldonado-Codina and Efron, 2004). Increased charge density often leads to increased effective pore size, which may promote diffusive penetration of lysozyme (Garrett et al, 2000).
Figure 2. Denatured proteins on an ionic hydrogel contact lens.
Silicone hydrogel contact lenses show reduced protein deposition but with a higher percentage of denatured lysozyme. This difference in deposition can be attributed to the hydrophobic nature and small pore size of silicone hydrogel materials (Senchyna et al, 2004).
Lipids and Lens Wettability
The meibomian glands secrete numerous lipids to form the lipid layer, and the composition varies among individuals (Lorentz and Jones, 2007). Research suggests that increased lipid deposition may be strongly related to decreased lens wettability (Sindt and Longmuir, 2007), which in turn is closely related to symptoms of dryness (Tonge et al, 2001). Rubbing and rinsing lenses with alcohol-based cleaners is effective in removing lipids, but lipids are not soluble in water-based cleaners (Sindt and Longmuir, 2007).
Because lipids attach to the hydrophobic areas of the lens surface, some patients who previously wore hydrogel lenses may experience more lipid deposition when wearing silicone hydrogel lenses (Figure 3), but this varies from patient to patient and from material to material. Indeed, compared with hydrogel materials, silicone hydrogel lens materials interact more with the hydrophobic lipid layer (Lorentz and Jones, 2007).
Figure 3. Lipid on silicone hydrogel lens after two weeks of wear.
The wettability of a contact lens affects how it interacts with the eyelid, and poor wettability increases the potential for increased deposition. Thus, increasing the wettability of the lens surface can improve lens-wearing comfort (Tonge et al, 2001).
Korb et al (2002) showed a positive correlation between the presence of lid wiper epitheliopathy (LWE) and symptoms of dry eye. LWE is a clinically observable alteration in the epithelium of the advancing lid margin, the lid wiper. In patients who have dry eye, the tear film is insufficient to separate the ocular surface and lid wiper (Korb et al, 2005), hence the lid wiper is subjected to trauma during the entire lid movement (Korb et al, 2002; Korb et al, 2005). Incomplete blinking may also contribute to the signs and symptoms of LWE (McMonnies, 2007). Prolonged intervals between blinks result in a thinner tear film with reduced lubricating properties, which leads to increased friction (McMonnies, 2007). As there is a strong correlation between the presence of LWE and lid parallel conjuctival epithelial folds (LIPCOF), it is thought that they share a common frictional origin (Berry et al, 2008; Pult et al, 2008). Therefore, LIPCOF and LWE may represent indirect, in-vivo measures of the coefficient of friction in contact lens wearers (Pult et al, 2010).
|Lens Care Solution-Induced Corneal Staining|
|A number of studies have reported corneal staining with certain combinations of polyhexa-methylene biguadine-preserved lens care solutions and silicone hydrogel contact lenses (Andrasko et al, 2006; Carnt et al, 2007; Garofalo et al, 2005). While some researchers suggest that care solution-induced corneal staining can lead to decreased comfort, others argue that low-grade corneal epithelial staining does not indicate solution toxicity (Ward, 2008). Solution-induced corneal staining remains a contentious topic, and lens-solution combinations should be selected on an individual basis.|
To increase lens wettability and wearing comfort, some practitioners instruct patients to lubricate their lenses with wetting drops before applying them, especially if the recommended care solution does not have a wetting agent (Cohen, 2004).
Care Solutions Designed for Comfort
Choosing a contact lens care system with regard to action, cytotoxicity, and biocompatibility may be as important to comfortable lens wear as is the lens itself. Many newer lens care solutions contain lubricating agents and surfactants specifically formulated to promote comfort upon application and to maintain wettability throughout the day. For example, Biotrue (Bausch + Lomb) contains hyaluronan, a conditioning agent that forms a hydrating network on the lens surface. The HydraGlyde Moisture Matrix in Opti-Free PureMoist (Alcon) enhances surface hydrophilicity and creates a continuous shield of moisture on the lens surface. Revitalens Ocutec (Abbott Medical Optics) features Ocutec activity that improves cleaning and can improve lens wearing comfort.
Cytotoxicity associated with some disinfecting agents and preservatives can cause discomfort and symptoms of dryness in lens wearers (Lievens et al, 2006). As a result of their recent study of preserved multipurpose care solutions, Choy et al (2012) suggested that practitioners advise patients using these products to rinse their soaked lenses with saline before applying them to avoid the potential for cytotoxic effects. Preservative-free care solutions, such as Synergi (Sauflon Pharmaceuticals Ltd.), or a one-step peroxide system are useful problem-solvers for patients who are not successful with multipurpose care solutions. Even though peroxide-based systems are used less frequently (Efron and Morgan, 2008), they cause fewer solution-related dry eye symptoms, are not toxic once neutralized, and are compatible with most soft lens materials (Carnt et al, 2007; Dalton et al, 2008; Dursun et al, 2002). For some materials, however, you may need to recommend additional surface cleaners.
The Comfort Equation
Research continues to validate what practitioners see every day in practice: uncomfortable contact lenses often create former lens wearers. An understanding of the factors that affect comfort—ocular dryness, lens deposits and wettability, cytotoxicity—and how to address them will help you keep your patients comfortable and happy in their lenses. Minimizing deposits through proper care solution and/or replacement schedule is vital. Avoiding preservatives and prescribing wetting agents to lubricate the ocular surface might also be promising. CLS
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