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Robert Tucker, Newton Samuel, Peter Lackey; Nile Red in different solvents can simulate contact lens wetting performance under different environments. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1457.
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© ARVO (1962-2015); The Authors (2016-present)
Silicone hydrogel (SiHy) lenses generally use one of two strategies to mask the hydrophobic silicone bulk and improve surface wettability: applying a true surface modification (i.e. delefilcon A, lotrafilcon B) or relying on embedded wetting agents to populate the lens surface (i.e. senofilcon A, narafilcon A). The effectiveness of each strategy for sustained wettability can be probed using the hydrophobic dye Nile Red (NR) to simulate contact lens surface interaction with hydrophobic materials (i.e. lipids). A high amount of staining could indicate potential areas for deposits and poor long-term surface wettability. To simulate a hydrophobic environment (i.e. after tear break-up), NR was dissolved in silicone oil. To simulate a hydrophilic environment (i.e. covered by tears), NR was suspended in an aqueous buffer. Ideally, a contact lens surface should be evaluated in both environments to fully understand the dynamics of its surface chemistry.
NR was dissolved in 1-propanol to make a stock solution. The stock was placed either in silicone oil (5 cSt, hydrophobic environment) or cholesterol assay buffer solution (aqueous environment) to make a NR suspension. Each lens type was rinsed in PBS, and dyed for 1 minute (NR/silicone) or 20 seconds (NR/aqueous). Each lens type was imaged using a fluorescent microscope and analyzed for NR surface coverage.
Control (non-surface modified silicone hydrogel lenses or silicone rubber sheets) showed high levels of staining. Lenses with a plasma surface treatment (i.elotrafilcon B) or a water gradient structure (i.e. delefilcon A) showed no staining in either environment. Products with embedded wetting agents (i.e. senofilcon A, narafilcon A) showed a moderate level (up to 20% surface coverage) of staining under silicone and aqueous conditions, indicating strong dye interaction in either environment.
Understanding the interaction of a contact lens surface with its environment is important. Both NR staining methods can be used to evaluate if a lens masking technique prevents silicone domain exposure when covered by tears, as well as when the surface has been exposed to a hydrophobic environment, such as after tear break-up. Both methods could be used to help predict long term surface performance.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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