Ultrasound biomicroscopy. I. Precision of measurements

To evaluate the precision of anterior chamber dimensions measured by the 50 MHz Humphrey Ultrasound Biomicroscope, the influence of various subprocedures, and the importance of clear definition of structures.

Fourty-eight right eyes of 26 normal subjects and 22 glaucoma patients were scanned centrally and at the chamber angle at three positions under standardized conditions. Eight different parameters were measured in angle images and two in images of central cornea and anterior chamber. Four variance components were calculated.

Measurement of the clearest defined structures had the highest precision. In angle images the precision expressed as the coefficient of variation was <21%, except for measurement of iris-ciliary process (range: 3-59%). All subprocedures contributed to the overall variance, image to image variation the most.

The precision of most measured parameters seems reasonable for clinical use. All subprocedures contributed significantly to the overall variance. The parameters that were related to clearly defined structures had the highest precision.