Investigating a New-generation Multipurpose Solution
This pilot study compares two lens care solutions for corneal staining, lens comfort and wearing time.
By William Townsend, OD, Sanford Katims, OD, and Jay S. Rosen, OD, FAAO

Bausch & Lomb recently introduced ReNu with MoistureLoc, its new-generation multipurpose solution. MoistureLoc utilizes alexidine, a small-molecular-weight biguanide, as a disinfectant. This marks alexidine's first use in a contact lens care product. It has a history of extensive use as a disinfectant in dentistry.

Small-molecular-weight compounds may gain entry into the contact lens matrix, and subsequent leaching of the disinfectant into the tear film during contact lens wear could conceivably cause corneal toxicity and increased corneal staining.

To investigate this issue and to determine whether the formulation of the new ReNu with MoistureLoc product eliminated the staining associated with ReNu MultiPlus, we conducted a brief three-center pilot study. Our practices are geographically diverse, located in the Northeastern, Southeastern and Southwestern United States.

Study Design

The 30 subjects in this study were experienced Acuvue 2 (Vistakon) lens wearers from our three practices. We selected Acuvue 2 as our test lens primarily because it's among the most frequently prescribed lenses in the United States. It's a Group IV lens, the most frequently prescribed group of hydrogel lenses.

We used our computer databases to randomly select the first 10 adult Acuvue 2 lens wearers. If any of these patients was unwilling or unable to participate, then we contacted the next patient on the list. We made no effort to select patients based on previous symptoms, signs or complaints. Participants received compensation in the form of free lenses at the conclusion of the study. The patients had used a variety of solutions before participating in the study; 12 had used ReNu/ReNu MultiPlus, 10 had used Opti-Free Express (Alcon), three had used Complete (Advanced Medical Optics) and two had used store brands. Three had no habitual solution brand.

The study utilized an open-label, cross-over design. We did not mask the solutions from observers or participants. We dispensed new Acuvue 2 lenses to patients for wear on a daily wear basis. We also provided each patient with either ReNu with MoistureLoc MPS or a control solution, Opti-Free Express. Opti-Free Express is preserved with Polyquad.

Figure 1. Mean staining scores for ReNu with MoistureLoc and Opti-Free Express

After two weeks of product use, we questioned patients about lens comfort and wearing time. We then performed slit lamp evaluation and recorded the results on standardized forms. Patients then received new lenses and were crossed over to the other test solution. After two weeks with the new lenses and solution, we questioned and evaluated the participants a second time.

We used slit lamp examination to assess corneal staining, using a corneal staining template to accurately measure the area of corneal staining. We also evaluated staining severity. We visually divided the cornea into five sections (central, superior, nasal inferior and temporal) and graded staining on a 0 to 4 scale in each section. We then totaled the numbers for each section in which staining appeared to calculate the area of staining.

We used a 100-point visual analog scale to rate overall contact lens comfort for each eye. The subjects rated comfort from "severe discomfort" (0) to "moderate awareness" (60) to "no awareness" (100). We used a similar scale to rate end-of-day lens comfort for each eye. Rating benchmarks ranged from "unusable" (0) to "good" (60) to "excellent" (100).

At the conclusion of the study, patients completed an exit questionnaire in which they compared the performance of the two study solutions for certain key attributes. For each question patients could indicate that the solutions were the "same" or they could choose one of the solutions.

Results

Corneal Staining In this study, corneal staining was greater in patients when using ReNu with MoistureLoc compared to when using the control, Opti-Free Express. In the majority of patients, mild staining was confined to one segment of the cornea. The mean staining grade for ReNu with MoistureLoc was 0.97 compared with 0.52 for Opti-Free Express. The mean staining area was 1.6 for all segments for ReNu with MoistureLoc while the mean staining area was 1.2 for all segments for Opti-Free Express (Figure 1).

Macropunctate staining was more frequently associated with ReNu with MoistureLoc than with Opti-Free Express. Sixteen eyes (26.7 percent) from patients using ReNu with MoistureLoc had staining grades of 2 (macropunctate) or higher in one or more segments of the cornea. One patient (1.6 percent) using Opti-Free Express had staining of this magnitude.

We calculated a "patient staining severity score" by multiplying the grade of staining by the area of staining, allowing a maximum of 20 points per eye or 40 points per patient. Using this calculation, mean staining severity for the total of two eyes was 5.3 for ReNu with MoistureLoc, while the mean staining severity score was 2.4 for Opti-Free Express. Six (20 percent) of the patients using ReNu with MoistureLoc had a severity score of 10 or higher. One (3.3 percent) patient using Opti-Free Express had a score of 10 or higher. This patient had a score of 18 with ReNu MoistureLoc and 10 with Opti-Free Express.

Wearing Time Wearing time was essentially the same for both products and appeared unrelated to staining severity. Patients had a mean habitual lens wearing time of 13.3 hours before the study, with a mean maximum time of 16.2 hours. Mean comfortable wearing time during the study was 13.4 hours for ReNu with MoistureLoc and 13.6 hours for the Opti-Free Express group.

Comfort Figure 2 shows responses to the patient preference questionnaires. The majority of patients found no difference between ReNu with MoistureLoc and the control solution for comfort upon lens application, ease of handling, making lenses feel cleaner or better vision. However, among participants who expressed a preference, a greater number preferred Opti-Free Express in several categories including overall comfort, keeping lenses comfortable for longer, ease of handling, better vision and reduced sensation of dryness.

We've found that visual analog scales are an effective way to quantify subjective patient response with minimal test bias. Ratings on the visual analog scales paralleled our patient preference results. The average patient rating for overall comfort on the visual analog scales was 78.8 for ReNu with MoistureLoc compared to 84.1 for Opti-Free Express. End-of-day comfort was rated 74.7 for ReNu with MoistureLoc compared to 81.1 for Opti-Free Express. Five of the six patients who had staining severity scores of 10 or higher preferred Opti-Free Express over ReNu with MoistureLoc in the areas of overall comfort and making lenses feel comfortable longer. The sixth patient rated the solutions the same.

Discussion

Figure 2. Staining severity scores for ReNu with MoistureLoc and Opti-Free Express.

This pilot study raises several issues that invite further exploration using a larger patient sample. We conducted our study using Acuvue 2, a widely prescribed Group IV lens. We observed staining of grade 2 or higher more frequently in patients using ReNu with MoistureLoc. Six of 30 patients using ReNu with MoistureLoc had staining scores of 10 or higher out of a maximum of 40.

Staining has been reported with the earlier formulation ReNu MultiPlus in silicone hydrogel lens wearers and in Group II hydrogel lens wearers, with the disinfecting ingredient PHMB suspected as the primary cause. Like PHMB, alexidine is a biguanide. The results of our study suggest that alexidine may have some of the same staining issues as PHMB. The small size of the alexidine molecule (800 Daltons) may allow absorption into the lens matrix, leading to the notable corneal effects we observed. We're interested to see how the MoistureLoc solution performs with silicone hydrogel and Group II lenses.

With only 30 patients enrolled, you should consider this a pilot study. We would strongly recommend subsequent studies be double-masked. Although our results are interesting, absolute conclusions regarding comfort preferences require larger patient samples and additional testing. In this study we failed to observe increased wearing time or better comfort with the new ReNu MoistureLoc solution despite its claimed benefits.

Five of the six patients who had staining scores of 10 or above favored the control. This is an intriguing area for follow up because staining at these levels has been reportedly asymptomatic. Perhaps the patients in our small sample were more sensitive to moderate degrees of staining than we anticipated. It's also possible that formulation differences in ReNu with MoistureLoc may have less impact on corneal sensitivity than other care products do. Despite numerous studies, the precise relationship between corneal staining and patient comfort remains poorly defined, but in our small study there was a preference for Opti-Free Express over Renu with MoistureLoc in patients who had more significant staining. A larger study could more thoroughly evaluate the statistical analysis of significant staining and comfort.

Conclusion

Our small multi-center open-label study conducted in three geographically diverse practices suggests that the use of ReNu with MoistureLoc in conjunction with wearing Acuvue 2 (Group IV) lenses may be associated with increased corneal staining when compared to Opti-Free Express, which contains a different disinfectant. Our study failed to demonstrate increased comfort or wearing time with the use of ReNu with Moisture Loc. Use of ReNu with MoistureLoc appeared to correlate with more corneal staining. Additional investigation is warranted to confirm and further explore the implications of these findings. CLS

This study was funded through Skunk Works Research by Alcon Laboratories, Inc.

Dr. Townsend is in private practice in Canyon, Texas, and is a consultant at the Amarillo VA Medical Center.

Dr. Rosen practices in a large general and surgical practice that provides full scope optometric and contact lens specialty care, medical eyecare and post surgical care.

Dr. Katims is in private practice in Port Washington, NY, currently attends Touro College of Law and lectures about silicone hydrogel lenses.

Contact Lens Spectrum, Issue: December 2005