Characterization of the force effect of aqueous and oily eye drops.

During the instillation of eye drops the drop impact affects a mechanical irritation on the eye surface. The force impact occurring in the moment of impact may be measured in vitro. Four commercially available eye drop preparations of different consistency and viscosity were tested. In dependance on the drip distance, the quantity of force impact was determined as well as the maximally effecting force during impact in each case. Whereas the force impact increased with all preparations with rising drip distance, only the higher viscosity solutions showed an approximate linear increase of the maximal force. With the aqueous low-viscosity eye drops, peak forces were ascertained. The drop oscillation was considered as the cause. The test results show that the consistency of eye drop preparations and their resulting physical-chemical properties like viscosity influence the quantity of the maximal force during the drop impact.