Direct optical measurement is emerging as a highly effective process analytical technology (PAT). This article provides an overview of the advancements in direct optical methods for measuring particle dynamics. The focus is on the following key areas: (1) configuration of hardware for image acquisition optical systems to ensure successful particle dynamics measurement; (2) challenges in infocus particle recognition processes, along with the development of image processing technology through three stages; and (3) uncertainties associated with all aspects of direct optical measurement, including image acquisition, processing, and analysis. This summary serves as a foundational basis for constructing and evaluating direct optical measurements for particle dynamics. Overall, these advancements highlight the potential impact of direct optical measurement on process analysis involving particles within various industrial applications.