Characterization of Particles in Suspension Eye Drops: Detection of Maximum Length of Irregular Particles

Suspension eye drops are a type of eye drop product in which the ingredients are not dissolved but are dispersed as particles. The Japanese Pharmacopoeia states that the maximum particle size is generally 75 μm or less.
The laser diffraction method is widely used in particle size distribution measurements, but measurement of the maximum particle length is not possible because the obtained results are expressed as the sphere equivalent diameter and particle images cannot be acquired by this method. As an additional problem, its detection capability for coarse particles that exist in trace amounts is not high.
This article introduces an example in which the maximum length of particles in a suspension eye drop product and a mixed sample of spherical and acicular particles were characterized by acquiring particle images and analyzing the particle shape, particle size distribution, and concentration with the Shimadzu iSpect DIA-10.