Alisa Sivak, MA, DipEd

Alisa assists the Centre for Contact Lens Research by writing and editing publications, reports, grant applications, and educational communications.

San Diego, USA

Joe Barr provided an overview of silicone hydrogels in a session on modern contact lens treatment, while Langis Michaud and Daniel Brazeau reviewed their benefits, material characteristics, new toric designs and potential adverse events in an overview of the newest lenses. Kelly Nichols included silicone hydrogels on a list of lenses having potential to help those who experience contact lens-related dry eye symptoms, in a lecture on comfort and ocular dryness in contact lens wear.

Part one of this synopsis focuses on paper and poster sessions addressing comfort, clinical signs and lens deposits.

Comfort and clinical signs

Two reports, one by Kate Weidemann and Carol Lakkis (Clinical Vision Research Australia) and the other by Tom Løfstrøm and Allan Kruse (private practitioners) indicate that the clinical perfromance of comfilcon A during CW is comparable to that of other silicone hydrogels. According to Colleen Riley (Vistakon) and colleagues (Visioncare Research Ltd.), symptomatic contact lens patients fit with senofilcon A lenses reported improvements in overall and end-of-day comfort as well as symptoms of dryness.  Results also showed improvements in limbal and bulbar hyperemia and corneal staining.

Peter Bergenske (Pacific University) and colleagues compared the clinical performance of galyfilcon A and omafilcon A lenses worn on a DW basis.  Both lenses induced the same improvements in clinical signs and comfort over subjects’ habitual, conventional hydrogel lenses. Another group led by Bergenske compared omafilcon A lenses with lotrafilcon B lenses, and found that both lenses performed well clinically.

Sally Dillehay (CIBA Vision) and colleagues reported the results of a 3-year, multi-site clinical trial comparing lotrafilcon A wearers with conventional hydrogel wearers.  Patients (neophytes and habituated lens wearers) who wore lotrafilcon A lenses for CW displayed long-term improvements in signs of corneal health and symptoms and a decrease in myopic progression, while papillary conjunctivitis, corneal staining and limbal redness increased in the neophyte cohort wearing low-Dk lenses on a DW basis.

Two reports, one by Kate Weidemann and Carol Lakkis (Clinical Vision Research Australia), and Tom Løfstrøm and Allan Kruse (private practitioners) indicate that the clinical performance of comfilcon A during CW is comparable to that of other silicone hydrogels. Comfilcon A is the most recent silicone hydrogel to be launched and is not yet approved for CW by the US Food and Drug Administration.
 
Jerome Ozkan and Eric Papas (Institute for Eye Research) reported that moderately symptomatic subjects wearing galyfilcon A lenses (on a DW, two-week replacement schedule) experienced less redness, burning/stinging and itching after instillation of a lubricant eye drop (Systane®) compared to a saline drop, pre- and post-lens wear. These subjects also reported improved comfort and less use of other rewetting drops throughout the day. 

William Reindel and colleagues (Bausch and Lomb) reported that ReNu® with MoistureLoc™ multipurpose solution (MPS) provided better comfort compared to a control MPS (Optifree® Express®) in subjects refit from conventional hydrogel to balafilcon A, lotrafilcon A and galyfilcon A lenses. The two solutions were associated with similar slitlamp findings.

Jaliah Varikooty and colleagues (CCLR) compared subjective symptoms and physiological responses in subjects using 2 different MPSs (alexidine- vs. polyquad-based) in subjects wearing balafilcon A lenses on a DW basis. Results showed no significant differences between the solutions in terms of corneal staining, deposits, lens wettability and bulbar or limbal hyperemia, though subjects reported that the alexidine-based system provided greater comfort and less dryness, particularly at the end of the day. 

Deposits

Patients who have difficulty complying with multi-step lens care regimens are often attracted to MPSs that do not require a ‘rub’ step. According to Cristina Schnider (Vistakon), adding a ‘rub’ step to both MPS and peroxide cleaning regimens improves the efficacy of solutions – even in a patient population prone to deposits.  In this study, galyfilcon A lens wearers with a baseline deposition grade of 3 or 4 dropped to 0% deposition when a ‘rub’ step was added to their care routine. 

Frank Zhang (CCLR) and colleagues evaluated the ability of 6 different ‘no rub’ MPSs to passively remove lysozyme from contact lens materials. After immersing lenses in radiolabeled lysozyme, lenses were left to soak for 8 hours in each MPS. The amount of lyzozyme remaining on each lens was measured and indicated that cleaning efficacy did not differ markedly between care regimens, but did vary between silicone hydrogel materials: the MPS had only 5-20% efficacy with most materials, but 30-50% efficacy with galyfilcon.

Lakshman Subbaraman (CCLR) and colleagues also used radiochemical analysis to determine lysozyme deposition as a function of time in Group IV, Group II and silicone hydrogel materials. Their results indicated that the kinetics of contact lens deposition depends on the chemical structure of lens materials:  lysozyme deposition occurs rapidly with group IV materials (ionic, high water content e.g. etafilcon A) before reaching a maximum, while silicone hydrogel and Group II materials (non-ionic, high water content e.g. omafilcon A) tend to accumulate lysozyme progressively without reaching a plateau.

Using a newly developed low acid strength buffer method to extract lysozyme from contact lenses, Mary-Ann Glasier and colleagues (CCLR) demonstrated that worn galyfilcon A lenses attract very low amounts of denatured lysozyme – similar to surface-treated silicone hydrogel lenses. This denatured lysozyme is more active, however, than the lysozyme found on other silicone hydrogel materials of lower water content, such as lotrafilcon A. Further work is needed to determine if this is due to the presence of an internal wetting agent incorporated within the matrix of these lenses.

Research indicates that silicone hydrogel materials attract lipids from the tear film, which can be a problem for some patients [see Protein and Lipid Deposition of Silicone-Hydrogel Contact Lens Materials]. Corrie Ziegler and colleagues (Ohio State University) are developing a method to extract lipid from worn silicone hydrogels for analysis by mass spectrometry. Their study shows that silicone hydrogels react differently to the chemicals conventionally used to extract lipid from contact lenses. The highest quality spectra is achieved by storage of silicone hydrogel lenses in methanol after they are removed, and the addition of chloroform just before analysis.

Stay tuned for Part Two of this synopsis, which includes sessions on adverse events, bandage lenses and piggyback combinations, and physiological effects of silicone hydrogels.

Part 2