Can a Lens Drop Minimize Deposits and Increase Comfort?
Recent clinical data indicate that a rewetting drop reduces protein deposition on soft contact lenses and improves comfort for both soft and GP lens wearers.
By Kenneth A. Lebow, OD, FAAO
Contact lens wearers use rewetting drops for many reasons including managing concurrent marginal dry eye symptoms, lens dehydration and its associated dryness, general ocular
lubrication, clearing away particulate matter and lens surface rewetting. Many rewetting drops are essentially saline solutions packaged in smaller bottles, although some rewetting drops may contain additional lubricants, wetting agents and cleaning components.
Some patients complain of increased lens awareness and blurred vision after only relatively short periods of daily lens wear. Patients also need effective rewetting drops immediately after overnight lens wear. While rewetting a hydrogel lens surface may temporarily increase its water content, improve patient vision and generally make the lens more comfortable, it does not necessarily clean the lens.
A rewetting drop that not only relieves symptoms but also minimizes deposits provides an advantage over drops that simply relieve symptoms. This paper will summarize some of the recent clinical and laboratory data that support these contentions.
Figure 1. General pattern of lysozyme accumulation on
extended wear contact lenses without cleaning
Looking Closer at Deposits
Clinically, the accumulation of contact lens deposits has been associated with increased patient signs and symptoms of lens discomfort. Clinicians have generally presumed that protein and other soilant deposits are factors that contribute to dryness and lens-induced discomfort.
A recent study evaluated how protein deposited on contact lenses throughout the first hours and days of wear. Subjects wore Acuvue
(Vistakon) lenses on an extended wear schedule and did not use lens care products during this study. The results demonstrated that protein accumulation generally appeared to reach a plateau after approximately one week of lens wear (Figure 1). However, individual deposit curves vary (Figure 2) and these individual differences are repeatable over time. Approximately 600µg of lysozyme deposits on Group IV lenses during the first 24 hours of wear. Another recent study demonstrated that clinical visual inspection of soft lenses during the first few weeks of wear does not help gauge lysozyme deposition on Group IV lenses. As practitioners, we must appreciate that, while the lenses our patients are wearing appear visibly clean, they are absorbing significant quantities of lysozyme that may cause both visual and anatomical problems. Keeping lenses clean throughout the day may minimize these problems and improve contact lens comfort.
Figure 2. Variability of individual lysozyme accumulation
More than a Rewetting Drop
Alcon designed its Clerz Plus rewetting drops to lubricate and rewet the lens surface as well as to minimize protein deposition during lens wear. In addition to hydrating ingredients, Clerz Plus contains a combination of two active surfactants (RLM-100 and Tetronic 1304), a citrate buffer that provides passive cleaning activity and the preservative Polyquad (Table 1). RLM-100 is a weak anionic (negatively charged) surfactant with surface-acting performance and micelle-forming ability, which emulsifies and disperses soilants including proteins, lipids and calcium deposits through electrostatic bonding. This allows the drop to clean and wet the surface of the lens. Tetronic 1304 is a wetting agent that lubricates the surface of the lens and acts as a surfactant that provides cleaning action primarily through hydrophobic and hydrogen-bond interactions.
Finally, citrate acts as a passive cleaner by enhancing the cleaning action of water molecules to help electrostatic interactions that facilitate the solubilization of soilants and displace polymer-bound
lysozyme. Thus, Clerz Plus uses ionic competition and displacement of lysozyme molecules by the citrate molecule in addition to the surfactant capability of the solution as its mechanism of action.
Minimizing Protein Deposits
Clerz Plus demonstrated its ability to clear away or inhibit protein buildup in a study that compared the efficacy of Clerz Plus to a historically popular rewetting drop, Bausch and Lomb Sensitive Eyes Drops. Fifty-nine patients wore Group IV lenses for either daily or extended wear. Daily wear patients cleaned their lenses with a dedicated cleaner each day while extended wear patients removed and cleaned their lenses weekly. Both groups used identical soaking, rinsing and storage solutions and no enzymatic cleaner during the month-long study. Only the rewetting drops that the patients used differed.
While subjective patient comfort and clinically evaluated lens cleanliness were essentially equivalent, high performance liquid chromatography
(HPLC) analysis demonstrated significantly lower micrograms of lysozyme (p¾0.01) on lenses of patients using Clerz Plus in both the daily and extended wear groups as compared to those using Sensitive Eyes Drops (Figure 3). The Clerz Plus formulation inhibited deposition or removed protein accumulation to a greater degree (20 percent less on average) than did the Sensitive Eyes Drops.
A Question of Comfort
The first question to address with any rewetting drops is whether it provides adequate relief from symptoms of dryness and lens-induced discomfort. Normal contact lens-wearing patients who could wear their lenses for at least eight hours each day evaluated the comfort of Clerz Plus in two clinical studies -- one with hydrophilic and one with gas permeable (GP) lenses. Researchers asked patients before the study began if they believed they had dry eyes and included the patients in the study regardless of their answer. Both studies masked the identity of the products from the investigators and the patients.
Investigators provided all patients with rewetting drops to use on an "as needed" basis. By allowing patients to determine usage frequency rather than directing them to use the drops a set number of times each day, the study sought to more closely approximate how patients would typically use the products in a real world, non-study environment.
Patients who used the rewetting drops completed a questionnaire about them. The questionnaire used a five-point Likert Scale in which 1 = "strongly disagree," 2 = "disagree," 3 = "undecided," 4 = "agree" and 5 = "strongly agree."
Hydrophilic Lens Study In this masked multicenter study, 231 patients wore either new Surevue
(Vistakon) (n=116) or new Soflens 66 (Bausch & Lomb) (n=115) lenses on a daily wear basis for 28 days without replacement. Half of the patients received
Opti-Free Express Multi-purpose Disinfecting Solution (Alcon) and half received ReNu MultiPlus Multi-purpose Solution (Bausch & Lomb) for the first 28-day study period. After 28 days and a one-week washout period, the patients received new lenses of the same brand and were crossed over to the other multipurpose solution. Throughout the study, researchers gave all patients the option to use Clerz Plus Rewetting Drops (masked with white labeling) "as needed." Patients rated Clerz Plus on days 14 and 28 with each regimen.
Table 2 summarizes the results for Clerz Plus with hydrophilic lenses. Patients positively rated the performance of Clerz Plus at day 14 and performance was maintained as lenses aged. Responses at day 28 were generally similar to those at day 14. Ninety percent of subjects using Clerz Plus in either treatment period agreed at day 28 that the Clerz Plus drop made their contact lenses feel more comfortable. Patients also determined that Clerz Plus helped prolong comfort throughout the day. A majority of patients agreed at day 28 that they "could wear their lenses longer" (79 percent), "lenses feel more comfortable at the end of the day" (67 percent) and "my eyes feel less dry at the end of the day" (68 percent) when using Clerz Plus.
Patients who self identified as having dry eyes found that Clerz Plus helped ease their symptoms while wearing lenses. In response to "This rewetting drop reduces the dry eye symptoms I experience when wearing my contact lenses," the percent who agreed increased from 73 percent at day 14 to 81 percent at day 28.
Results of this study indicate that patients can successfully use Clerz Plus with both
PHMB-based systems such as ReNu MultiPlus and with Poly-quad-based Opti-Free Express
MPDS. Clerz Plus kept lenses hydrated and eyes feeling less dry and more comfortable both during the day and at the end of the day.
Figure 3. Lysozyme levels for daily and extended wear lenses after one month of rewetting drop
GP Lens Study This multicenter study evaluated the performance of Clerz Plus when compared to Boston Rewetting Drops (Bausch & Lomb), a historically popular drop that does not contain a protein inhibitor. In a parallel randomized study design, investigators assigned 105 established GP wearers to use a regimen of Boston (Original) Conditioning Solution (Bausch & Lomb) and Boston Daily Cleaner (Bausch & Lomb) for 90 days and provided Boston Rewetting Drops to use
p.r.n. Investigators gave another 103 patients Unique-pH Conditioning Solution
(Alcon) and SupraClens Daily Protein Remover (Alcon) to use for 90 days and provided Clerz Plus to use
p.r.n. Both investigators and patients were masked to the identity of the products. Patients completed a Likert questionnaire at days 14, 45 and 90.
Table 3 summarizes the GP study results. Most users of both drops agreed that the rewetting drops provided immediate relief upon usage ("My contact lenses feel more comfortable after I use this rewetting drop") at days 14, 45 and 90.
Patient satisfaction with Clerz Plus increased throughout the study. At day 14 Boston and Clerz Plus both had similar attribute ratings for end-of-day performance. By day 90, Clerz Plus had surpassed Boston for agreement on end of day comfort ratings. For example, agreement with the statement, "This rewetting drop makes my lenses more comfortable all day long" increased 22 points from 50 percent at day 14 to 72 percent at day 90 for the Clerz Plus users. In contrast, Boston users' agreement increased only seven points from 47 percent at day 14 to 54 percent at day 90. A similar pattern occurred for other comfort attributes: "My contact lenses feel more comfortable at the end of the day when I use this rewetting drop" (66 percent agree for Clerz Plus, 52 percent for Boston) and, "My eyes feel less dry at the end of the day when I use this rewetting drop" (63 percent agree for Clerz Plus, 54 percent for Boston).
Among patients who self identified as having dry eyes when wearing lenses, Clerz Plus rated higher than Boston Drops for its ability to reduce dry eye symptoms experienced when wearing lenses. Clerz Plus gained 100 percent agreement at day 14 and 90 percent agreement at day 90. Patients rated Boston 67 percent at day 14 and 78 percent at day 90.
Results of these clinical studies indicate that Clerz Plus works well to extend comfort and relieve dry eye symptoms for both hydrophilic and GP lens wearers. It appears especially helpful for reducing contact lens-related dry eye symptoms and for promoting end of day comfort, allowing patients to wear lenses more comfortably throughout the day.
The increased ratings for Clerz Plus as the lenses aged is intriguing. It may be that patients who used the drops "as needed" developed a more effective dosing regimen as the study went on. However, this would not explain why performance of Clerz Plus increased over the 90 days more than that of Boston drops. Perhaps the rewetting components in Clerz Plus, specifically Tetronic 1304, play a role. In the Clerz Plus formulation, the surfactant Tetronic 1304 also serves as a hydrating agent to hold moisture on the surface of both hydrophilic soft and hydrophobic GP lenses. The effects of the soft lens multipurpose disinfecting solution
(Opti-Free Express) and the GP conditioning solution (Unique-pH) may have also contributed to these results.
Beyond hydration, protein removal may have played a role in preserving comfort. Just as daily and enzyme cleaners become more important to comfort, presumably by removing large amounts of protein, as lenses are kept longer, we could reasonably assume that protein inhibitors in a rewetting drop applied throughout the day can influence comfort by removing smaller amounts of protein and other materials as they accumulate throughout the day. Perhaps the ability of Clerz Plus to inhibit protein from building up during the day becomes more important as the lenses age. This could apply to the Group IV Surevue lenses that attract large amounts of protein and to a lesser extent with the Soflens 66 and GP materials which tend to attract less protein.
Most contact lens wearers report end of day
(EOD) dryness as a major reason for early removal of their lenses. A rewetting drop that improves EOD dryness and is well tolerated by patients may effectively reduce patient symptoms and increase comfortable wearing time.
These studies indicate that many patients can experience relief from contact lens-related dry eye symptoms, better end of day comfort and comfortable lens wear longer into the day by using Clerz Plus. Rewetting drops such as Clerz Plus that combine hydrating and protein-inhibition agents may improve lens performance for these patients.
To receive references via fax, call (800) 239-4684 and request document #99. (Have a fax number ready.)
Dr. Lebow is in private
practice in Virginia Beach, VA, where he specializes in fitting advanced contact lens designs. He serves as a
consultant to Alcon and has participated in Alcon-
sponsored clinical studies.
Contact Lens Spectrum, Issue: November 2003