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June 2005


The Effect of Tear Components on the in vitro Wettability of SH Lenses

D.L. Meadows, H.A. Ketelson, N. McQueen and R.P. Stone (Consumer Products Research, Alcon Laboratories, Inc., Fort Worth, TX)


Purpose: A sessile drop technique was utilized to measure in vitro advancing contact angles as an indicator of silicone hydrogel lens wettability in the presence of artificial tear solutions ( ATS). The influence of lysozyme, albumin and mucin were studied for their effect on the wettability of Acuvue® AdvanceTM (AA), Focus N&D and O2 Optix lenses presoaked in three commercial multipurpose solutions ( MPS), Opti–Free® Express®, Renu® MoistureLocTM, Aquify® and an investigational MPS.

Methods: Advancing contact angles were determined via a sessile drop method using a high speed video system with curve fitting software. The lenses were cycled through ATS–air exposures to simulate clinical blinking conditions. MPS products were used according to the manufacturers’ listed regimen.

Results: Silicone hydrogel lens materials displayed different wettabilities and it was believed that their differences in surface chemistry modification technologies were one of the main factors responsible for this. The contact angles of AA lenses increased to over 100° during lens cycling in saline or ATS solutions. Comparatively, new Focus and Optix lenses displayed lower contact angles and this indicated improved wettability relative to the AA lens material. The ATS components mucin and lysozyme had no effect on the contact angles of the lenses whereas albumin played an important role when lenses were preconditioned with particular surfactants. The effect of preconditioning the lenses in MPS showed different effects on the material wettabilities. This was believed to be a reflection of the different polymers and surfactants in the marketed products and their interactions with the lens materials. Specific physico–chemical interactions taking place between the contact lens material, tear components and formulation components were believed to be important aspects that play a role in the wettability of the silicone hydrogel materials.

Conclusions: This study indicated that SiH lens materials display different wettabilities depending on the type of surface modification technology and preconditioning solution. The effect of ATS components such as lysozyme and mucin showed no impact on improving the wettability of the lenses. Comparatively, albumin had a significant impact on improving the wettability of the lens materials when used with preconditioning agents.

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