An ongoing study of pachymeters has been carried out to determine the accuracy, reproducibility, and ease of operation of various optical and ultrasonic pachymeters. Beginning with optical versus available ultrasonic pachymeters, the demonstrated greater accuracy and reproducibility of ultrasound led to enlargement of the study to a comparison of all available ultrasonic pachymeters. Side-by-side evaluation was undertaken to determine interobserver variation and a number of other factors. The results are summarized as a guide.