Objective quantification of cataract and subjective assessment of visual performance are essential features of anticataract or cataractogenic drug trials. The constraints of a longitudinal trial require a compromise in contrast sensitivity measurement between sensitivity and speed. Such a system has been developed for use in longitudinal anticataract trials. An objective cataract assessment system has also been developed for these trials. Visual performance parameters and objectively measured grades of cataract using these systems were correlated in a group of patients with early lens opacities. Overall the correlation was poor in all three morphological types of cataract. Possible reasons for this and implications for future anticataract trials are discussed.