Contact lenses are rapidly coated with a variety of proteins, lipids, and mucins.1–8 The first event observed at the interface between a contact lens and tear fluid is protein adsorption.9,10 Of late, studies examining the interaction of tear proteins and, to a lesser extent, lipids with contact lenses have become important fields of research, following the widespread use of contact lenses in many physiological and pathologic conditions.
Silicone hydrogel (SH) contact lenses transmit significantly more oxygen than conventional poly HEMA-based materials,11–13 and were developed to meet the desire for lenses that could safely provide overnight wear for up to 30 continuous nights. In addition to oxygen transmission, adequate contact lens wettability is critical to achieving long-term physiological compatibility and successful, problem-free contact lens wear.14 With conventional lens materials, wettability reduces over the wearing period and replacing a lens frequently results in the maintenance of a more wettable, “cleaner” surface.15–17 SH lenses are inherently more hydrophobic than conventional poly HEMA-based hydrogels18,19 and require a surface modification process to provide a hydrophilic, wettable surface.20,21 More recent attempts to deal with the surface hydrophobicity has involved the incorporation of high-molecular-weight polymers such as polyvinyl pyrrolidone (PVP) into the SH material, which act to mask the underlying silicone and improve the surface wettability through the PVP moving to the lens material interface.22,23 As a result of this inherent hydrophobicity, SH materials deposit greater quantities of lipid than conventional hydrogel materials,24 which may act to negate the impact of the surface treatment process and result in a surface that rapidly dewets after a blink, resulting in increased sensations of dryness.
One of the potential means of modifying the lens surface to enhance wettability is to treat the lens with an external wetting agent such as a surfactant. Surfactant-containing contact lens care systems are extensively used within the contact lens care industry for cleaning purposes. However, because of the ability of surfactants to associate at interfaces, it is possible that surfactants will also adsorb onto the surface of hydrogels and thus potentially influence surface wetting characteristics. 25 These effects may have significant implications in terms of perceived patient comfort on both initial insertion and at the end of the wearing period. To date, only two studies have examined this effect, one based on an in vitro analysis25 and the other an ex vivo clinical study.26 These studies provided sound evidence that surfactant association at hydrogel lens interfaces play a significant role in controlling wettability and provided confirmation that surfactants can positively influence initial lens comfort. This has particular relevance in the context of continuous wear (CW), in which lenses are left in situ for up to 30 nights without removal. If a drop were available that could be inserted at various times during the day that would reduce deposition of tear film components and improve wettability, then it could be used on a regular basis and eliminate the need for periodic removals for lens cleaning, which would have significant benefits for the patient using materials in such a manner.
Thus, the purpose of this study was to investigate the impact of treating SH lenses during their wearing period with a novel rewetting agent that has been specifically developed to reduce in-eye deposition on poly HEMA-based materials.27 In-eye comfort, in vivo wettability, and the deposition of the lens materials with protein were determined against a control rewetting drop (RWD) without any active agents. The results obtained provide valuable information about the potential for surface modification of these polymers in situ and the impact this has on subjective lens comfort.
MATERIALS AND METHODS
Ethics clearance was obtained through the Office of Research Ethics at the University of Waterloo before commencement of the study. This study was conducted as a controlled, investigator-masked, open-label, 2-month prospective trial using a randomized crossover design. A total of 24 subjects (soft lens wearers who had either no experience with CW or who had not worn lenses on a CW basis for at least previous 3 months) completed the study (mean age, 33.8 ± 11.2 years). Participants were all healthy and had no history of complications with their existing contact lenses. Participants were refitted with Focus Night & Day (FND) lenses (lotrafilcon A; CIBA Vision, Duluth, GA.), which were worn on a CW basis for up to 30 consecutive nights. Subjects for whom an acceptable lens fit could not be obtained were excluded from the study. CIBA Vision AOSEPT and CIBA Vision SoftWear saline were issued to each participant in case they had to perform unscheduled removals during the 30-day CW period. Subjects were issued two differing contact lens RWDs in a random order, which were each inserted four times per day. The test product was OPTI-FREE RepleniSH rewetting drops (Alcon Laboratories, Fort Worth, TX) containing a variety of surface active agents (Table 1), and the control article was a sterile, single-dose nonpreserved saline product, (Minims saline; Bausch & Lomb, Rochester, NY), which contains no active agents. The drops were used for two consecutive 1-month periods with lenses being replaced and a new set issued after the first month.
After a maximum of 30 days CW, participants slept at least one night without lenses before resuming CW with a fresh pair of lenses. At the same time, the solutions were crossed over and the worn lenses were collected for protein analysis. Clinical visits were conducted on collection (baseline) and after 14 and 28 days with each pair of lenses, at which time clinical performance was determined by a comprehensive slit lamp examination and subjective satisfaction was derived through the use of subjective analog scales.
Assessment of Subjective Comfort
Subjects completed 100-mm analog scales at each visit to evaluate symptoms and comfort experienced with the study lenses and the RWDs. The severity was indicated on a scale from zero to 50, zero being the best rating or no symptoms and 50 being the worst rating or maximum symptoms. The following variables were evaluated on waking, in the middle of the day, at the end of the day, and on insertion of the drops: lens comfort, dryness, redness, tearing, burning, and itching. The following variables were evaluated in the middle of the day, at the end of the day, and on insertion of the drops: blurry vision, fluctuating vision, and cloudy/filmy vision. In addition, mucous discharge on waking and stinging on insertion of the drops were also evaluated. At the final study visit, participants were asked to complete an exit questionnaire to indicate which drops provided better lens comfort and whether they had a preference for one of the rewetting solutions.
Visual acuity was measured monocularly using logarithm of the minimum angle of resolution visual acuity at high contrast and low contrast under high illumination (approximately 800 lx). Temporal bulbar hyperemia of both eyes was measured using a SpectraScan PR-650 spectroradiometer (Photo Research Inc., Chatsworth, CA). Prelens tear film noninvasive breakup time (PLTF NIBUT) with the lenses in place and non-invasive tear breakup time (NIBUT) after lens removal were assessed using a TEARSCOPE plus (Keeler Ltd., Berkshire, U.K.). Overall wettability of the contact lenses in vivo was graded on a scale of zero to 4, in which zero related to a lens exhibiting “perfect wettability” and 4 a lens with “severely reduced” wettability. Posterior lens mucin ball response was graded on a zero to 4 scale using the CCLR photographic Mucin Ball Grading Scale for reference.28
The ocular surface was examined using a slit lamp with and without fluorescein. Before fluorescein instillation, the investigator graded the limbal and bulbar conjunctival hyperemia on a scale of zero to 100 for each quadrant. On instillation of fluorescein, the severity of corneal staining in each of five corneal zones was graded using a zero (negligible) to 100 (severe) scale, and the percentage of each zone that exhibited staining was graded using a zero (none) to 100% (total) score. Conjunctival staining was graded on a scale of zero to 100 for each quadrant. The tarsal conjunctiva was evaluated for hyperemia and papillae on a scale of zero to 100 for each quadrant or region.
Collection of Worn Contact Lenses
On completion of the 28-day wearing period, lenses were collected aseptically (using nonpowdered surgical gloves) and placed in individual, sealed glass vials. The lenses were placed in 1.5 mL of a 50:50 mixture of 0.2% trifluoroacetic acid and acetonitrile (ACN/TFA)29,30 and, for the purposes of this study, only the protein data derived from the lenses removed from the right eye are described.
Reagents and Materials.
PhastSystem components were described previously.30 Immuno-Blot polyvinylidene difluoride (PVDF) membranes were purchased from Bio-Rad Laboratories (Mississauga, Ontario, Canada). Polyclonal rabbit anti-human lysozyme was purchased from Cedarlane Laboratories (Hornby, Ontario, Canada) and goat anti-rabbit IgG-HRP was purchased from Sigma (St. Louis, MO.). Human lysozyme (neutrophil), chicken egg lysozyme, and lyophilized Micrococcus lysodeikticus cells were also purchased from Sigma. Bovine serum albumin standard was obtained from Pierce Biotechnology Inc. (Rockford, IL). All other reagents purchased were of analytical grade.
Protein Deposit Extraction and Sample Processing After Extraction
Lenses collected in ACN/TFA were incubated in the dark at room temperature for 24 hours. Two 0.70-mL aliquots of ACN/TFA was transferred to sterile Eppendorf tubes and lyophilized to dryness in a Savant Speed Vac (Halbrook, NY). Dried protein pellets were stored at –70°C before reconstitution. Before electrophoresis/Western blotting and lysozyme activity analysis, lyophilized protein pellets were reconstituted in modified reconstitution buffer–MRB (10 mM Tris-HCl; 1 mM EDTA, with 0.9% saline) pH 12.0 and BioStab Biomolecule Storage Solution (Sigma Aldrich).31
Electrophoresis and Immunoblotting
Lysozyme standards were prepared fresh on the day of analysis from a 1.0 μg/μL frozen stock of purified human neutrophil lysozyme with MRB pH 8.0 and subjected to sodium dodecyl sulfate–polyacrylamide gel electrophoresis followed by Western blotting to PVDF membranes as described previously.30,31
Negative Control–Extraction and Western Blot Analysis of Unworn Lenses
Three new, unworn FND lenses were extracted in ACN/TFA solution and were subjected to sodium dodecyl sulfate–polyacrylamide gel electrophoresis and Western blotting.
Measurement of Lysozyme Activity
The extracts were assayed for lysozyme activity using a fresh suspension of Micrococcus lysodeikticus for each sample as described previously30 but with the following modifications. Micrococcal cells were suspended in 50 mM sodium phosphate buffer (pH 6.3) to an initial optical density of 1.0 at 450 nm (Multiskan Spectrum ELISA Plate Reader fitted with a microcuvette; ThermoLabsystems). Standards and samples were applied to 1-mL cells in 10 μL or less. Kinetic measurements were taken at 30-second intervals (450 nm) for 5 minutes at 30°C with stirring for 10 seconds after each measurement except time zero. Human neutrophil lysozyme standard (5, 10, 50, 100 ng) was run concurrently with samples. The change in absorbance was plotted against time, from 30 seconds to between 3 and 5 minutes, to determine the slope or initial velocity. A native lysozyme standard curve was constructed of mass lysozyme standard against initial velocity by least squares. The mass of active lysozyme in contact lens extracts was then extrapolated from the native lysozyme standard curve.
Measurement of Total Protein Deposition
Amido Black Dot Blot protein assay was used to determine total protein in neutralized ACN/TFA extracts. Nitrocellulose membranes (Bio-Rad Laboratories) were pretreated with 15% (v/v) phosphoric acid and 10% (v/v) methanol for 1 minute, blotted between two sheets of filter paper, and air-dried at room temperature. Membranes were wet in water and positioned into the Bio-Dot Microfiltration Apparatus (Bio-Rad Laboratories). Bovine serum albumin standards were prepared fresh by diluting a 2.0 mg/mL stock standard in phosphate-buffered saline at pH 7.2 (concentrations ranging between 0.5 and 16 μg/mL). Samples and standards were applied to membranes in 50-μL volumes. Wells were rinsed once with phosphate-buffered saline (100 μL). Membranes were then air-dried, fixed (1.5% glutaraldehyde for 5 minutes), and rinsed in NaOH (2×) and 0.05% (v/v) HCl (1×) before immersion in Amido Black Stain (0.1% [w/v] amido black, 5% [v/v] methanol, 10% [v/v] glacial acetic acid) for 1 to 2 minutes, destained (40% [v/v] methanol, 10% [v/v] glacial acetic acid), and air-dried. Stained dot blots were imaged (Syngene Gene Genius Gel Documentation System with GeneSnap) under white light and quantified by densitometry using Gene Tools.
Statistical analysis was conducted using Statistica 7 software (StatSoft Inc., Tulsa, OK). All data are reported as mean ± standard deviation and range unless otherwise indicated. Table 2 describes the statistical analysis in detail. Clinical data were analyzed using a repeated-measures analysis of variance (RM-ANOVA) and post hoc Tukey HSD tests to compare OPTI-FREE RepleniSH rewetting drops versus the control drops. For the subjective symptoms and vision symptoms that were assessed three times during the day, a four-way RM-ANOVA was conducted with symptoms, drop type, visits, and time of the day as factors. For symptoms on drop insertion, a three-way RM-ANOVA was conducted with symptoms, drop type, and visit as the factors. A Student t-test was used to determine statistically significant differences between the two care regimens for the analytical data. For the cases in which multiple t-tests were undertaken, Bonferroni corrections were undertaken.
Several factors showed no significant difference between products. There were no significant differences between drops for high contrast visual acuity (p = 0.77), low contrast visual acuity (p = 0.98), bulbar hyperemia using the SpectraScan PR-650 spectroradiometer (p = 0.47), PLTF NIBUT (p = 0.81), NIBUT (p = 0.40), in situ wettability (p = 0.12), conjunctival hyperemia (bulbar, p = 0.68 and limbal, p = 0.84), corneal staining (p = 0.20), or conjunctival staining (p = 0.14).
The following symptoms were compared: lens comfort, dryness, redness, tearing, burning, and itching. All six symptoms were rated by participants at the 14-day and 28-day visits, on waking, in the middle of the day, and at the end of the day (Figure 1). On waking, lenses were less comfortable and had greater symptoms of dryness than at any other time of the day (p < 0.001). By midday, comfort and dryness symptoms had improved and these symptoms progressively got worse as the day progressed (p < 0.001 for comfort and p = 0.001 for dryness). Redness ratings were higher (redder) on waking than at noon (p = 0.002). There was also a small, but statistically significant, change in symptoms over the period of the study. Subjective lens comfort on waking at 28 days was rated better than comfort on waking at the 14-day visit (p = 0.03). No other differences in symptoms changed over time (p > 0.25). Subjective dryness on waking at the 14-day visit versus dryness on waking at 28-day visits approached statistical significance (p = 0.05), with the 14-day visits achieving higher ratings (worse).
There was no significant difference between the two products for overall lens comfort over the period of the study (p = 0.13).
Subjective Symptoms on Insertion of the Drops
The following 10 symptoms on drop insertion were assessed: lens comfort, dryness, redness, tearing, burning, itching, blurry vision, fluctuating vision, cloudy/filmy vision, and stinging. These symptoms were rated at both 14-day and 28-day visits.
Lens comfort on insertion was rated significantly better with OPTI-FREE RepleniSH drops than with the control drops (p = 0.02). This interaction is shown in Figure 2.
Subjective Vision Ratings
The symptoms blurry vision, fluctuating vision, and cloudy/filmy vision were assessed, all having been rated at noon and at the end of the day, both at 14-day and 28-day visits. There was a significant difference between ratings at noon and at the end of the day (p = 0.01), with visual symptoms getting worse at the end of the day. The interaction between drops and symptoms approached statistical significance (p = 0.08). On performing a Tukey HSD post hoc test, blurry vision and cloudy/filmy vision were rated significantly better with the test RWD than with the control drops. Figure 3 displays the interaction between these three symptoms and drops.
Participants rated mucous discharge on waking at the 28-day visit to be worse with the control drops than with the test RWD (3.6 ± 7.4 vs. 8.0 ± 11.9; p = 0.02).
Table 3 summarizes the participants’ preference. The values reflect the number of participants who preferred OPTI-FREE RepleniSH, the control drops, or none. No statistically significant difference was found between preferences (chi square = 3.00 for better comfort and 3.25 for overall preference).
There was no difference between drops with regard to redness of the upper tarsus (p = 0.59). However, there was a significant interaction between drops and visits with regard to lower tarsal redness (p = 0.04). The trend indicated that with the test RWD, redness was graded the same at the 14-day and the 28-day visit, whereas with the control drops, redness was graded higher at the 28-day visit than at the 14-day visit. However, post hoc analysis did not reach significance (14-day vs. 28-day visit, p = 0.09).
The superior section of the upper tarsal conjunctiva was graded rougher with the control drops than with OPTI-FREE RepleniSH (28.5 vs. 26.5, p = 0.01). However, there was no overall difference between drop types for lower lid roughness (p = 0.36).
Lysozyme Deposition on Lenses
Table 4 details the lysozyme deposition on the lenses when subjects used the two products. The results demonstrate that lysozyme deposition was significantly greater when subjects used unpreserved saline compared with when they used OPTI-FREE RepleniSH (p < 0.001).
Assessment of Lysozyme Activity
A summary of the lysozyme activity results is presented in Table 5. The percentage of denatured lysozyme was significantly reduced when subjects used OPTI-FREE RepleniSH drops compared with when they used the control drops (p < 0.01).
Table 6 details the total protein deposition found on the lenses. Total protein deposited on the lenses was significantly greater when MINIMS sodium chloride was used compared with when they used OPTI-FREE RepleniSH (p < 0.001).
To date, this study is the first of its type that has examined the potential use of RWDs containing surface active agents with SH lenses, although a recent study has investigated the positive effects of a saline-containing drop on the comfort associated with conventional lens materials,32 and another study has examined the influence of pretreating conventional lens with a conditioning drop on the ocular response over the course of a day.33 Dryness and discomfort remain significant problems for wearers of SH lens materials, particularly as the day progresses,34–38 and this has a negative impact on lens wettability.39,40 This study investigated the impact of treating SH lenses during their wearing period with a novel rewetting agent that has been specifically developed to reduce in-eye deposition and enhance subjective comfort.
A variety of clinical factors were found to be improved in subjects who were using the test RWD (OPTI-FREE RepleniSH), namely improved lens comfort after drop insertion (Fig. 2), less blurry/cloudy vision (Fig. 3), reduced mucous discharge on waking, and reduced palpebral lid changes. The most probable reason for the enhanced subjective comfort when the subjects used the test RWD relates to the ability of the surface active agent to associate at the lens material interface and improve the surface wetting of the lens material.25,39 The instillation of the test RWD results in adsorption of the surface active agent (Tetronic 1304) to the lens material, thereby increasing the wettability of the lens surface.25 These results are in agreement with a recently published in vitro study,25 which indicates that hydrogel surfaces treated with Tetronic 1304 produces enhanced wettability, irrespective of the presence of lysozyme. In light of the fact that the study was conducted as an open-label study, the potential bias that subjects may show subjectively must not be discounted, and some subjects may have preferred the “test” drop rather than the “control” drop for this reason. However, although subjective data may be influenced, objective results will not be biased; and these indicated that lysozyme deposition, percentage of lysozyme denaturation, and total protein deposition were all significantly reduced when subjects used the test RWD compared with the control saline drop.
The subjective results detailed in Figure 1 are unexpected, because it would typically be assumed that comfort and dryness would reduce over the period of the month with lenses. This result may be because of some adaptation effects occurring over the period of the month to stiffer siloxane-based lens materials. The data presented in this article would suggest that future studies in which silicone hydrogel lenses are a “test” article would benefit from an adaptation period in which eyes would be adapted to the lens material before the commencement of the study.
As detailed in Table 1, OPTI-FREE RepleniSH includes a number of components that are intended to passively and actively remove tear film deposits from the lens surface. These include citrate, which has been previously shown to passively remove protein from group IV lenses.41–43 Polyethylene glycol-11 lauryl ether carboxylic acid (also called RLM-100) is a surfactant designed to remove protein and lipids; poloxamine is a surface-modifying surfactant designed to remove protein and aid in surface wetting.39 Finally, Tetronic 1304 helps lenses to retain moisture and also helps to shield the lens from future protein buildup.25,27 Theoretically, it has been suggested that surfactants would alter the interfacial chemistry at the molecular layer between the contaminant and lens. After this, polar micelles would form and they would entrap the debris, enabling them to be rinsed away.44 Clinically, solutions containing a surfactant have been reported to promote mechanical cleaning as well as provide ongoing cleaning during wear.45–47
Table 5 indicates that the amount of denatured lysozyme recovered from lotrafilcon A lenses was 76% ± 10% when the subjects used the test RWD, which was significantly lower than when subjects used the control drops (85% ± 7%). The degree to which protein denaturation occurs is mediated by a number of factors, including contact time with the substrate, chemical composition of the substrate, protein type, surrounding pH, and temperature. Proteins are most likely to denature when exposed to strongly hydrophobic surfaces.48–53 The use of a surfactant containing RWD will have increased the hydrophilicity of the contact lens surface, resulting in deposited lysozyme being exposed to a lesser hydrophobic surface,25 resulting in lower denaturation. Although a previous study that investigated the relationship between conventional hydrogel lens wettability and in vivo deposition did not find any significant correlation between the two,54 a recent in vitro study55 has shown that proteins such as albumin had a significant impact on improving the wettability of the SH lens materials, whereas components such as lysozyme and mucin showed no impact on improving the wettability of these lenses. Further systematic in vivo studies are needed to investigate the effect of contact lens care systems containing surfactants and other surface active agents on subjective comfort, wettability, and in vivo deposition of components other than lysozyme and determine the relationship between these factors.
Given the known link between protein deposition and immunologic changes induced during lens wear,56–58 it is possible that reduced protein deposition and a reduction in denatured lysozyme could result in reduced mucous discharge and palpebral lid changes, as found in this study. Given the short duration of this study, these results do seem remarkably consistent and strongly suggest that practitioners should consider prescribing RWDs with surfactants and other surface active agents to patients who use lenses on a continuous-wear basis.
In conclusion, our data suggests that the composition of the OPTI-FREE RepleniSH rewetting drops has a beneficial effect on both the deposition of proteins onto the lotrafilcon A material and also on subjective satisfaction. This has tremendous clinical implications in that practitioners should strongly consider providing RWDs containing surfactants and other surface active agents to subjects who wear SH lens materials on an overnight basis. Further work is required to determine if this important clinical finding is transferable to those patients who use SH on a daily-wear basis.
Michelle Senchyna is now an employee of Alcon, who sponsored the study conducted, while she had a faculty appointment at the University of Waterloo.
This work was funded by a Collaborative Research and Development Grant from Natural Sciences and Engineering Research Council of Canada (NSERC) and Alcon Research Limited.
This work was presented as a poster at ARVO 2004, Fort Lauderdale, Florida.
Centre for Contact Lens Research
School of Optometry
University of Waterloo
200, University Avenue West
Waterloo, Ontario, N2L 3G1, Canada
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