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Muhammad Abdulrazik, Simon Benita; Interfacial Interactions Of Cationic And Anionic Artificial Tears With Ionic Hydrogel Contact Lens Surface. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6111.
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Contact lens wear is a predisposing factor to dry eye. However, no artificial tear product is approved for use while wearing contact lenses due to biocompatibility concerns. Ionic and non-ionic hydrogel and silicon hydrogel soft contact lenses are the most common in current clinical use. This study aims at investigating interfacial interactions between cationic and anionic artificial tear preparation and the surface of ionic hydrogel contact lenses.
The two studied ionic contact lenses were FDA category III and IV hydrogel lenses (Hanita, pHEMA/MAA, 38% and 57% water content respectively). The studied formulations with electrostatic charge were Refresh EnduraTM anionic emulsion (Allergan) and Cationorm® cationic emulsion (Novagali Pharma). The studied reference formulations were HyloComod® (Ursapharm), HypoTears® (Novartis), GenTeal® (Novartis), Refresh® (Allergan) and Saline 0.9%. Contact lens was mounted on freshly excised rabbit eye globe. Contact angles were measured by FTA 125 system (First Ten Angstroms Inc.), formulation surface tension was determined by multiwell plate tensiometer (Kibron Inc.) and spreading coefficients were calculated from measured surface tensions and contact angles. Kruskal-Wallis test was used for determination of significance (P less than 0.05).
For each studied formulation, contact angles were significantly lower on 57% water content (WC) compared with 38% WC lens. Contact angle scores on both contact lenses were lowest for the cationic emulsion (27.16±3.54 on 38% WC surface and 8.98±2.32 on 57% WC surface), which significantly outperformed the anionic emulsion (49.47±4.73 on 38% WC surface and 17.68±1.94 on 57% WC surface). However, contact angle scores for the anionic emulsion were significantly lower than the non-charged formulations on each contact lens (from 63.41±4.4 [REFRESH] to 80.76±2.43 [HYPOTEARS] on 38% WC surface, and from 45.25±0.68 [REFRESH] to 62.02±4.39 [HYPOTEARS] on 57% WC surface).
The effect of contact lens water content on contact angles was steeper than the effect of formulation electrostatic charge. However, comparison between formulation on each of the studied surfaces have shown the superiority of the cationic emulsion that achieved approaching-zero spreading coefficients (-3.32 ± -0.85 and -0.38 ± -0.19 mN/m, for 38% and 57% WC surface respectively) (spreading coefficient = 0 represents a spontaneous and complete wetting), suggesting that electrostatic attraction have a strong impact on interfacial interaction between instilled eye drop and contact lens surface. The results support the utilization of cationic-charge approach in the design of tear substitutes for contact lens wearers.
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