Ultrasound biomicroscopy. III. Accuracy and agreement of measurements

PURPOSE: To estimate the accuracy of measurements by the 50 MHz Humphrey Ultrasound Biomicroscope and evaluate the agreement of measurements by ultrasound biomicroscopy and optical pachometry. METHODS: The accuracy was estimated by comparing measurements by ultrasound biomicroscopy with more exact mechanical methods. Forty-seven PMMA intraocular lenses and 52 distances between horizontal separated sutures were measured. The agreement between ultrasound biomicroscopy and optical pachometry was evaluated by comparing measurements of central cornea thickness and anterior chamber depth of 46 eyes. RESULTS: The axial measurements by ultrasound biomicroscopy was on average 10 microm higher than the reference method (SEM 3 microm). The lateral measurements was without systematic difference from the reference method (SEM 5 microm). The mean central corneal thickness was considerably higher by optical pachometry, 557+/-5 microm (SEM), than by ultrasound biomicroscopy, 533+/-5 microm. Similarly for anterior chamber depth where mean measurements were 2955+/-66 microm and 2897+/-63 microm, respectively. CONCLUSIONS: The axial and lateral accuracy of ultrasound biomicroscopic measurements was good. The agreement between measurements obtained by ultrasound biomicroscopy and optical pachometry was poor in this investigation. Several circumstances could be accountable for this.