A model for quantifying difficulty in squeezing eyedrops from their containers.

Difficulty in squeezing eyedrops from bottles has been acknowledged as leading to reduced compliance. The purpose of this study was to develop objective means for assessing the force needed to extract eyedrops from bottles and to compare agents from the same pharmacological groups. A leverlike apparatus was designed for measurement of the required force. Comparing several topical agents, 3 bottles from the same batch were tested in a masked fashion and mean values were calculated. A total of 41 topical agents from 6 pharmacological groups were studied. The force required to squeeze an eyedrop ranged widely, from 700 to 2550 g. Significant differences (P<or=.05) were found within each pharmacological group. In conclusion, assessing the force needed to extract eyedrops is simple and repeatable. Significant differences were demonstrated among agents; however, the clinical relevance of these differences has yet to be proved.