Study on the Usability of Ophthalmic Solutions (I)

The Variation in Squeezing Force and Drop Volume

Abstract

We examined the usability of eleven brands of ophthalmic solution available on the market. This involved measuring the squeezing force on ophthalmic solution containers and drop volume using a force gauge. We also examined the usability of the ophthalmic solution containers for our subjects with regard to the ease of squeezing out the contents. The squeezing force on containers differed among products, ranging from 0.7 kg (Tobramycin) to 2.9 kg (Levocabastine hydrochloride). For five products, there was a large change in the squeezing force on the container between the beginning and the end of the usage period, the coefficients of variation of which ranged from 6.9 % to 16%. The drop volume differed among products ranging from 34 mg (Ibudilast, Tropicamide) to 49 mg (Levofloxacin). There were three products with a large change in the drop volume during the usage period, the coefficients of variation of which ranged from 12.2% to 22.2%. Ibudilast had a particularly large change in drop volume during the usage period. The usability test with our subjects showed that usability decreased when the squeezing force for a container was 1.5 kg or more. Our findings showed that it would be effective to use the variation in the squeezing force and drop volume during the usage period as an index when evaluating the usability of ophthalmic solutions.