Abstract

SA.17.06

Physical characteristics of lubricant eye drops

Marcus Mittag1, Gabriele Karsten2, Rudolf Guthoff1, Detlef Behrend2
1Universitäts-Augenklinik Rostock, 2Institut für ImplantatTechnologie und Biomaterialien e.V., Rostock-Warnemünde

Objective
The Dry Eye is a big therapeutic challenge for every clinical ophthalmologist. There are a lot of innovative therapeutic approaches. The local therapy with lubricant eye drops however plays currently the most important role. For their functionality, among other things, the dynamic viscosity and the wettability are important. The dynamic viscosity plays a role during the blinking process, the wettability, when the drop is inserted and between the blinking process.
Methods
Physical measurements in 43 samples of over the counter lubricant eye drops were performed. Under standardized conditions the dynamic viscosity and the contact angle as a parameter of the wettability were measured. The viscosity was analyzed with a rheometer (RheoStress1/ Thermo Haake), the contact angle with the principle of the lying drop (contact angle system OCA20/ dataphysics). The measurement of the contact angle was performed on glass and as a model of the surface of the eye on a hydrophilic contact lens.
Results
A main part of the analyzed preparations showed, exept some special solutions (2 preparations < 10 mPa *s, 7 preparations 100-300 mPa *s, 4 preparations 3500-4000 mPa *s, 1 preparation  41000 mPa *s), a dynamic viscosity around 70 mPa*s.  The analyzed contact angles showed different characteristics between the preparations and between glass and contact lens.
Conclusions
In the utilisation of lubricant eye drops currently the main focus is set on the dynamic viscosity. But beside the viscosity the wettability and the film stability under shear stress play an essential role. Both parameters should not only be regarded isolated of each other, but also with regard to the biological functionality in interaction with the ocular surface always in context. The parameters show distinct differences in the analyzed preparations and have an influence on the effect of the lubricant eye drops – considering the individual status of the patient.

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