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U. Doshi, J. Xu; Effect of Viscosity, Surface Tension and Mucoadhesion on Ocular Residence Time of Lubricant Eye Drops. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4641.
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To evaluate physico-chemical properties of lubricant eye drops such as viscosity, surface tension and mucoadhesion and their effect on ocular residence time.
VISINE® TEARS® Long Lasting Dry Eye Relief and several marketed lubricant eye drops products were evaluated in terms of surface tension (pendant drop measurement) and mucoadhesion (rheology of eye drops mixed with mucin). An in vivo gamma scintigraphy study on rabbits was also conducted to evaluate the ocular residence time of the eye drops. These results were assessed against a consumer preference study, in which long lasting effect was rated by consumers.
The consumer preference study evaluated formulations of various viscosities ranging from1-70 cps. The consumers rated the 10 cps viscosity formulation, VISINE® TEARS® Long Lasting Dry Eye Relief, longer lasting than Refresh Liquigel® which is > 50 cps. The same VISINE® TEARS® Long Lasting Dry Eye Relief formulation was tested in an in-vivo gamma scintigraphy study in rabbits, and was also found to last longer as compared to Refresh Liquigel®. This finding is in contrast to the belief that higher viscosity formulations have longer ocular residence time. As a result, physico-chemical properties other than viscosity, such as surface tension and mucoadhesion were also studied.In a surface tension study, VISINE® TEARS® Long Lasting Dry Eye Relief was evaluated together with Refresh Tears®, and Systane Free®. It was found that VISINE® TEARS® Long Lasting Dry Eye Relief has a surface tension of 44 dyne/cm, which is close to human natural tears. Systane Free and Refresh Tears have much higher surface tension. The low surface tension of VISINE® TEARS® Long Lasting Dry Eye Relief may be responsible for its spreading ability, better adhesion to the cornea and long lasting.In another study to assess the mucoadhesive properties of the hypromellose-based VISINE® TEARS® Long Lasting Dry Eye Relief formulation, it was found that it possesses significant mucoadhesive property, whereas the carboxymethyl cellulose-based Refresh Tears® showed negligible mucoadhesive property.
The above results suggest that higher viscosity alone does not necessarily yield longer lasting eye drops. Lower surface tension, which is related to good wettability and spreading property of the eye drops, and mucoadhesion all contribute to long lasting properties. This conclusion is consistent with the findings obtained in in vitro, animal, and consumer use studies.
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