Effectiveness of No-Rub Contact Lens Cleaning on Protein Removal: A Pilot Study

Purpose. To compare the amount of protein deposits adhering to human-worn soft contact lenses, using the untreated contact lens from the contralateral eye as controls, to investigate the capabilities of the No Rub contact lens cleaning systems in protein removal from soft contact lenses.

Methods. New 1 Day Acuvue soft contact lenses were worn on a daily-wear basis by 16 Hong Kong Chinese volunteers on 5 separate days. Four right lenses of each subject were treated with No Rub contact lens cleaning systems (Alcon Opti-Free Express, Alcon Opti-Free Express No Rub Lasting Comfort Formula, B&L ReNu MultiPlus, and Ciba Vision SOLO Care Plus). The total amount of protein was extracted from all contact lenses and analyzed by the Bradford assay.

Results. Among the contralateral contact lenses, there was no significant difference in the total protein extracted (TPE; 11.2 ± 3.8 vs. 12.6 ± 5.2 mg/ml, p = 0.20). There was a significant positive correlation in TPE between two lenses worn by the same volunteer (R² = 0.84, y = 0.79 x + 1.3, p < 0.001). Lenses treated with Opti-Free Express and Opti-Free Express No Rub Lasting Comfort Formula solutions had significantly less TPE (7.3 ± 5.2 and 6.7 ± 4.1 mg/ml, respectively, p < 0.001) than the untreated contralateral lenses (12.7 ± 6.8 and 13.2 ± 5.3 mg/ml, respectively). No statistical difference in TPE was detected in the lenses treated with ReNu MultiPlus (13.0 ± 7.8 mg/ml, p = 0.49) and Solo Care Plus (12.1 ± 8.7 mg/ml, p = 0.99) solutions when compared with their untreated contralateral lenses (13.0 ± 7.8 and 12.1 ± 8.7 mg/ml, respectively).

Conclusions. Not all no-rub contact lens solutions were shown capable of removing the protein deposit from soft contact lenses.

Proteins are a major source of soft contact lens contamination, and contact lens protein deposits have been implicated in poor tolerance of contact lenses and in immunologic occurrences such as giant papillary conjunctivitis. ^1-3 One of the major concerns of contact lens care systems is whether the lens is adequately cleaned. Contact lens care systems have relied traditionally on a digital cleaning-and-rinsing step after lens removal. Recently, several commercially available no-rub contact lens cleaning systems have been introduced into the market. These systems were promoted to be capable of removing protein deposits from the soft contact lenses, even without digital rubbing. The elimination of the rubbing step offers the advantage of convenience and enhances patient compliance.

To the best of our knowledge, no study has been carried out to investigate the capabilities of no-rub contact lens cleaning systems in protein removal from human-worn contact lenses. Previous investigations have focused on in vitro conditions, ^{4, 5} in which the contact lenses were incubated in artificial tears solutions. Results obtained from in vitro conditions have limited application to the living eye, because discrepancies such as lens surface drying and lid-wiping action do exist between experimental conditions and the living eye. In vivo protein combinations may lead to different deposition processes than in vitro protein groups, depending on pH, ion concentration, and other chemical differences between human tears and artificial tears solutions. Contralateral contact lenses were generally used for direct comparison in in vivo contact lens studies ^6-9 on the assumption that there is no significant difference in tear-protein adhesion between contralateral contact lenses. However, this assumption has been challenged, in that a significant difference in tear-protein adhesion to contact lenses between the two eyes of the same individual had been reported. ¹⁰ One of the objectives of this pilot study was to compare the amount of protein deposits adhering to human-worn soft contact lens. Then, using the untreated contact lens from the contralateral eye as controls, the second objective was to investigate the capability of no-rub contact lens cleaning systems in protein removal from human-worn soft contact lenses.

METHODS

Subjects

We enrolled 18 subjects (6 male and 12 female) aged 18 to 32 years in the study. Informed consent was obtained from all subjects after a full explanation of the procedures. All subjects had less than -1.00 D of astigmatism and had previously worn soft lenses. Subjects with eye diseases, allergies, insufficient lacrimal secretions, preexisting ocular infections, or a history of problems with lens wear and pregnant subjects were all excluded. All subjects were fitted with Acuvue daily disposable soft contact lenses (groups IV, ionic lens material containing 42% etafilcon A and 58% water) from Vistakon (Jacksonville, FL) ranging from -1.50 to -9.00 D (mean, -4.50 D). They were worn for specific time periods (about 10 hours). Each lens was removed with plastic-tipped forceps and placed in a glass vial containing sterile nonpreserved nonbuffered saline. Before protein extraction and analysis, four right lenses of each subject were treated with no-rub contact lens cleaning systems (Alcon Opti-Free Express, Alcon Opti-Free Express No Rub Lasting comfort formula, Alcon Laboratories, Fort Worth, TX; Bausch & Lomb ReNu MultiPlus, Rochester, NY; and CIBA Vision Solo Care Plus, CIBA Vision Canada Inc., Mississauga, Ontario, Canada). The vials were then capped, labeled, and taken to the laboratory for extraction and protein analysis within 10 days of collection.

Extraction and Analysis of Total Protein

Extraction of proteins from lenses.

Lenses were removed from the vials, and excess storage solution was blotted with bibulous paper. Lenses were placed in microtubes (Axygen Scientific, Inc., Union City, CA) with 1 ml of a 50:50 mixture of 0.2% trifluoroacetic acid (Sigma-Aldrich Corp., St. Louis, MO) and acetonitrile (Merck & Co., Inc., Whitehouse Station, NJ). Lenses were allowed to soak in the extraction solution for 48 hours, and then the extraction solution was analyzed. A new contact lens, which was treated by the same extraction method, was used as a control.

Bradford assay.

The Bradford assay was used for the determination of total protein deposits from the lens. Lens-extracted samples were analyzed directly upon proper dilution. A 0.8-ml aliquot of sample was mixed with 0.2 ml of Bradford reagent (Bio-Rad Laboratories, Hercules, CA) and incubated at room temperature for 30 minutes. The absorbance of the mixture was measured at 590 nm using a spectrophotometer (Universal micro-plate reader ELx 800 UV, Bio-Tek Instruments, Inc., Winooski, VT). A standard curve established with bovine serum albumin was used for the quantification of protein.

Statistical Analysis

The data were analyzed using Student's t test (paired or unpaired, two-tailed), linear regression (least-squares method), and correlation analysis (Pearson's correlation coefficient).

RESULTS

All data are presented in Table 1. There was no significant difference between the total amounts of protein extracted from contralateral contact lenses (paired t test, p = 0.20). Mean total protein extracted was significantly lower from the samples treated with Opti-Free Express and Opti-Free Express No Rub lasting Comfort Formula solutions than from the untreated contralateral lens samples (p < 0.001). Although total protein extracted tended to be10% less from the lenses treated with Opti-Free Express No Rub lasting Comfort Formula solution than from the lenses treated with Opti-Free Express solution, the difference was statistically insignificant (unpaired t test, p = 0.29). No statistical differences were found in total protein extracted from the lens treated with ReNu MultiPlus (p = 0.49) and SOLO Care Plus (p = 0.99) solutions compared with the untreated contralateral lenses.

Table 1

DISCUSSION

A principal finding of the present study is that there were comparable amounts of tear-protein adhesion to contact lenses between the two eyes of the same individual, suggesting the feasibility of using a pair of contralateral contact lenses for direct comparison in a clinical contact lens study. Not all contact lens cleaning solutions were shown to be capable of protein removal from soft contact lenses.

Previous investigations on the performance of different contact lens cleaning systems on protein removal were conducted in vitro using artificial tears solutions. ^{4, 5} They showed that most commercial contact lens cleaning systems were capable of removing protein deposits from soft contact lenses by following the manufacturer's instruction with ⁴ or without ⁵ the rubbing step. However, the in vitro nature of these investigations has the major drawback that one cannot evaluate the capabilities of the cleaning systems under human physiological conditions, in which native proteins interact with the contact lens. Right and left contact lenses have generally been used for comparison in contact lens studies regarding protein deposit adhesion to different contact lens materials. ^6-9 We addressed the challenge to comparing results from contralateral contact lens samples, and we found that comparable amounts of protein were extracted from contact lenses from the two eyes of each subject. A larger sample size is necessary to confirm this conclusion.

The second part of our study was to investigate the capabilities of different no-rub cleaning systems in removing protein deposits from soft contact lenses without the rubbing step. These cleaning systems allow the patient to forgo rubbing the lens if the lens is rinsed extensively and soaked for 6 hours or more. The use of a no-rub care process would increase patient compliance due to the simplicity of the procedure and the relatively small amount of time required. In this pilot study, we studied four no-rub cleaning systems and found that not all of them were capable of protein removal from the soft contact lenses. Only lenses treated with Opti-Free Express and Opti-Free Express No Rub Lasting comfort formula solutions were found to have less protein extracted than the untreated contralateral lenses. Opti-Free Express No Rub Lasting comfort formula, which contains a surfactant cleaner, promoted as helping to shield the lens surface from protein deposition, tended to remove 10% more protein deposits than did Opti-Free Express, but this difference was not statistically significant. It should be noted that high-water-content ionic contact lenses (Acuvue daily disposable; Jacksonville, FL) were used in this pilot study. These contact lenses contain methacrylic acid, which imparts a negative charge to the material and thermodynamically favors the deposition of positively charged species such as lysozyme. This results in attracting substantially greater quantities of protein than do other groups of contact lenses. ^{9, 11, 12} The efficacy of the contact lens cleaning systems on protein removal may be different with different contact lens materials. Because this pilot study has investigated four care systems on one lens material, the efficacy of these or other systems on protein removal from other groups of contact lens is worth further investigation with a similar protocol. In conclusion, not all no-rub contact lens solutions were found capable of removing the protein deposits from soft contact lenses.

ACKNOWLEDGMENTS

The authors would like to thank Alcon Hong Kong, Ltd., for supply of the contact lens solutions.

The authors have no direct or indirect proprietary interests in contact lens solutions investigated in the study.