Contact Lens Spectrum Supplements

Special Edition 2016

Contact Lens Spectrum

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C O N T A C T L E N S S P E C T R U M S P E C I A L E D I T I O N 2 0 1 6 c l s p e c t r u m . c o m 47 positively-charged cationic dyes including Alcian Blue (AB) (Tas, 1977) and Stains All (E9379, Sigma- Aldrich, St. Louis, MO) (Homer et al, 1993), which have been successfully used to determine HA concentration in aqueous solution (Fagnola et al, 2009), but not to visualize HA on silicone hydrogel contact lens surfaces. HYALURONAN AND SILICONE HYDROGEL CONTACT LENSES To characterize the interactions of HA with silicone hydrogel lenses, two common analytical microscopy techniques, atomic force microscopy (AFM) and confo- cal scanning laser microscopy (CSLM) in conjunction with safranin dye, a biological Gram's stain that binds HA and that silicone hydrogel lenses readily sorb, were used. Inherently wettable senofilcon A and samfilcon A, as well as plasma-treated balafilcon A were also im- aged after soaking in 0.1% (w/v) pure HA solution or Biotrue MPS. (Lenses were soaked overnight in Biotrue MPS per the package insert to mimic the manu- facturer recommended lens cleaning regimen, while an identical set of lenses were soaked in pure HA solution.) Biotrue MPS is a sterile, isotonic solution contain- ing 0.1% (w/v) HA mucopolysaccharide, zwitterionic sulfobetaine detergent, and Tetronic 1107 poloxamine surfactant (K083757). The synergistic combination of sulfobetaine, Tetronic 1107, and HA increases lens surface wettability. Tetronic 1107 associates with etafil- con A contact lens surfaces and is retained for at least 8 hours in vitro (Tonge et al, 2001). Similar to Tetronic 1107, HA associates with lens surfaces as evidenced by continuous elution from different lens materials for up to 20 hours (Scheuer et al, 2010). inherently wettable but differ in water content, surface morphology, and surface chemistry, while plasma- treated balafilcon A has distinct wettable and non- wettable domains islands (Gonzalez-Meijome et al, 2006; Teichroeb et al, 2008; Lopez-Alemany et al, 2002). HA sorbed on silicone hydrogel contact lenses (Scheuer et al, 2010) may improve lens performance by maintaining lens wettability. Biotrue MPS (Bausch + Lomb) contains relatively high molecular weight (HMW) HA (MW = 1.4MDa) (Liu et al, 2016), which may in part explain why it read- ily associates with both conventional and silicone hydro- gel CLs during lens storage, then elutes into artificial tear fluid in vitro over a 20-hour period (Scheuer et al, 2010). Clinically, this results in elevated HA concentra- tion in the tears of senofilcon A lens wearers 2 hours after first inserting lenses that had been soaked overnight in Biotrue MPS (Scheuer et al, 2016). Because these studies suggest that HA may persist on the lens over the course of daily wear, its physical interaction with the sili- cone hydrogel is of great interest. While chemical chromatography methods are used to measure the concentration of HA dissolved in solution, characterization of surface-localized HA is primarily qualitative and microscopy-based, notably optical (Tas, 1977) and confocal (Luo and Prestwich, 2001) microscopies. Negatively-charged HA readily binds Figure 2. AFM section analysis of balafilcon A before and after overnight incubation with 0.1% (w/v) pure HA solution. Samples were characterized in dry state by soft taping in air. Sorbed HA uniformly covers the surfaces of the hydrogels, filling the pits to decrease pit depth and decreasing surface roughness. Figure 1. AFM topographical images of dry balafilcon A (A,B), senofilcon A (D,E), and samfilcon A (G,H) SiHy lenses at small and large scan size, respectively; images after overnight incubation with 0.1% (w/v) pure HA solution of balafilcon A (C), senofilcon A (F), and samfilcon A (I) SiHy lenses at high magnification. Sorbed HA levels the surface morphology observed on fresh lenses. HY ALURONAN IN LENS CARE

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